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<HTML>
<CENTER><A HREF = "Section_start.html">Previous Section</A> - <A HREF = "http://lammps.sandia.gov">LAMMPS WWW Site</A> - <A HREF = "Manual.html">LAMMPS Documentation</A> - <A HREF = "Section_commands.html#comm">LAMMPS Commands</A> - <A HREF = "Section_howto.html">Next Section</A>
</CENTER>
<HR>
<H3>3. Commands
</H3>
<P>This section describes how a LAMMPS input script is formatted and what
commands are used to define a LAMMPS simulation.
</P>
3.1 <A HREF = "#3_1">LAMMPS input script</A><BR>
3.2 <A HREF = "#3_2">Parsing rules</A><BR>
3.3 <A HREF = "#3_3">Input script structure</A><BR>
3.4 <A HREF = "#3_4">Commands listed by category</A><BR>
3.5 <A HREF = "#3_5">Commands listed alphabetically</A> <BR>
<HR>
<A NAME = "3_1"></A><H4>3.1 LAMMPS input script
</H4>
<P>LAMMPS executes by reading commands from a input script (text file),
one line at a time. When the input script ends, LAMMPS exits. Each
command causes LAMMPS to take some action. It may set an internal
variable, read in a file, or run a simulation. Most commands have
default settings, which means you only need to use the command if you
wish to change the default.
</P>
<P>In many cases, the ordering of commands in an input script is not
important. However the following rules apply:
</P>
<P>(1) LAMMPS does not read your entire input script and then perform a
simulation with all the settings. Rather, the input script is read
one line at a time and each command takes effect when it is read.
Thus this sequence of commands:
</P>
<PRE>timestep 0.5
run 100
run 100
</PRE>
<P>does something different than this sequence:
</P>
<PRE>run 100
timestep 0.5
run 100
</PRE>
<P>In the first case, the specified timestep (0.5 fmsec) is used for two
simulations of 100 timesteps each. In the 2nd case, the default
timestep (1.0 fmsec) is used for the 1st 100 step simulation and a 0.5
fmsec timestep is used for the 2nd one.
</P>
<P>(2) Some commands are only valid when they follow other commands. For
example you cannot set the temperature of a group of atoms until atoms
have been defined and a group command is used to define which atoms
belong to the group.
</P>
<P>(3) Sometimes command B will use values that can be set by command A.
This means command A must precede command B in the input script if it
is to have the desired effect. For example, the
<A HREF = "read_data.html">read_data</A> command initializes the system by setting
up the simulation box and assigning atoms to processors. If default
values are not desired, the <A HREF = "processors.html">processors</A> and
<A HREF = "boundary.html">boundary</A> commands need to be used before read_data to
tell LAMMPS how to map processors to the simulation box.
</P>
<P>Many input script errors are detected by LAMMPS and an ERROR or
WARNING message is printed. <A HREF = "Section_errors.html">This section</A> gives
more information on what errors mean. The documentation for each
command lists restrictions on how the command can be used.
</P>
<HR>
<A NAME = "3_2"></A><H4>3.2 Parsing rules
</H4>
<P>Each non-blank line in the input script is treated as a command.
LAMMPS commands are case sensitive. Command names are lower-case, as
are specified command arguments. Upper case letters may be used in
file names or user-chosen ID strings.
</P>
<P>Here is how each line in the input script is parsed by LAMMPS:
</P>
<P>(1) If the last printable character on the line is a "&" character
(with no surrounding quotes), the command is assumed to continue on
the next line. The next line is concatenated to the previous line by
removing the "&" character and newline. This allows long commands to
be continued across two or more lines.
</P>
<P>(2) All characters from the first "#" character onward are treated as
comment and discarded. See an exception in (6). Note that a
comment after a trailing "&" character will prevent the command from
continuing on the next line. Also note that for multi-line commands a
single leading "#" will comment out the entire command.
</P>
<P>(3) The line is searched repeatedly for $ characters, which indicate
variables that are replaced with a text string. See an exception in
(6). If the $ is followed by curly brackets, then the variable name
is the text inside the curly brackets. If no curly brackets follow
the $, then the variable name is the single character immediately
following the $. Thus ${myTemp} and $x refer to variable names
"myTemp" and "x". See the <A HREF = "variable.html">variable</A> command for
details of how strings are assigned to variables and how they are
substituted for in input script commands.
</P>
<P>(4) The line is broken into "words" separated by whitespace (tabs,
spaces). Note that words can thus contain letters, digits,
underscores, or punctuation characters.
</P>
<P>(5) The first word is the command name. All successive words in the
line are arguments.
</P>
<P>(6) If you want text with spaces to be treated as a single argument,
it can be enclosed in double quotes. The quotes are removed when the
single argument is stored in its final form. See the <A HREF = "dump_modify.html">dump modify
format</A> or <A HREF = "if.html">if</A> commands for examples. A "#"
or "$" character that is between double quotes will not be treated as
a comment indicator in (2) or substituted for as a variable in (3).
</P>
<HR>
<H4><A NAME = "3_3"></A>3.3 Input script structure
</H4>
<P>This section describes the structure of a typical LAMMPS input script.
The "examples" directory in the LAMMPS distribution contains many
sample input scripts; the corresponding problems are discussed in
<A HREF = "Section_example.html">this section</A>, and animated on the <A HREF = "http://lammps.sandia.gov">LAMMPS WWW
Site</A>.
</P>
<P>A LAMMPS input script typically has 4 parts:
</P>
<OL><LI>Initialization
<LI>Atom definition
<LI>Settings
<LI>Run a simulation
</OL>
<P>The last 2 parts can be repeated as many times as desired. I.e. run a
simulation, change some settings, run some more, etc. Each of the 4
parts is now described in more detail. Remember that almost all the
commands need only be used if a non-default value is desired.
</P>
<P>(1) Initialization
</P>
<P>Set parameters that need to be defined before atoms are created or
read-in from a file.
</P>
<P>The relevant commands are <A HREF = "units.html">units</A>,
<A HREF = "dimension.html">dimension</A>, <A HREF = "newton.html">newton</A>,
<A HREF = "processors.html">processors</A>, <A HREF = "boundary.html">boundary</A>,
<A HREF = "atom_style.html">atom_style</A>, <A HREF = "atom_modify.html">atom_modify</A>.
</P>
<P>If force-field parameters appear in the files that will be read, these
commands tell LAMMPS what kinds of force fields are being used:
<A HREF = "pair_style.html">pair_style</A>, <A HREF = "bond_style.html">bond_style</A>,
<A HREF = "angle_style.html">angle_style</A>, <A HREF = "dihedral_style.html">dihedral_style</A>,
<A HREF = "improper_style.html">improper_style</A>.
</P>
<P>(2) Atom definition
</P>
<P>There are 3 ways to define atoms in LAMMPS. Read them in from a data
or restart file via the <A HREF = "read_data.html">read_data</A> or
<A HREF = "read_restart.html">read_restart</A> commands. These files can contain
molecular topology information. Or create atoms on a lattice (with no
molecular topology), using these commands: <A HREF = "lattice.html">lattice</A>,
<A HREF = "region.html">region</A>, <A HREF = "create_box.html">create_box</A>,
<A HREF = "create_atoms.html">create_atoms</A>. The entire set of atoms can be
duplicated to make a larger simulation using the
<A HREF = "replicate.html">replicate</A> command.
</P>
<P>(3) Settings
</P>
<P>Once atoms and molecular topology are defined, a variety of settings
can be specified: force field coefficients, simulation parameters,
output options, etc.
</P>
<P>Force field coefficients are set by these commands (they can also be
set in the read-in files): <A HREF = "pair_coeff.html">pair_coeff</A>,
<A HREF = "bond_coeff.html">bond_coeff</A>, <A HREF = "angle_coeff.html">angle_coeff</A>,
<A HREF = "dihedral_coeff.html">dihedral_coeff</A>,
<A HREF = "improper_coeff.html">improper_coeff</A>,
<A HREF = "kspace_style.html">kspace_style</A>, <A HREF = "dielectric.html">dielectric</A>,
<A HREF = "special_bonds.html">special_bonds</A>.
</P>
<P>Various simulation parameters are set by these commands:
<A HREF = "neighbor.html">neighbor</A>, <A HREF = "neigh_modify.html">neigh_modify</A>,
<A HREF = "group.html">group</A>, <A HREF = "timestep.html">timestep</A>,
<A HREF = "reset_timestep.html">reset_timestep</A>, <A HREF = "run_style.html">run_style</A>,
<A HREF = "min_style.html">min_style</A>, <A HREF = "min_modify.html">min_modify</A>.
</P>
<P>Fixes impose a variety of boundary conditions, time integration, and
diagnostic options. The <A HREF = "fix.html">fix</A> command comes in many flavors.
</P>
<P>Various computations can be specified for execution during a
simulation using the <A HREF = "compute.html">compute</A>,
<A HREF = "compute_modify.html">compute_modify</A>, and <A HREF = "variable.html">variable</A>
commands.
</P>
<P>Output options are set by the <A HREF = "thermo.html">thermo</A>, <A HREF = "dump.html">dump</A>,
and <A HREF = "restart.html">restart</A> commands.
</P>
<P>(4) Run a simulation
</P>
<P>A molecular dynamics simulation is run using the <A HREF = "run.html">run</A>
command. Energy minimization (molecular statics) is performed using
the <A HREF = "minimize.html">minimize</A> command. A parallel tempering
(replica-exchange) simulation can be run using the
<A HREF = "temper.html">temper</A> command.
</P>
<HR>
<A NAME = "3_4"></A><H4>3.4 Commands listed by category
</H4>
<P>This section lists all LAMMPS commands, grouped by category. The
<A HREF = "#3_5">next section</A> lists the same commands alphabetically. Note that
some style options for some commands are part of specific LAMMPS
packages, which means they cannot be used unless the package was
included when LAMMPS was built. Not all packages are included in a
default LAMMPS build. These dependencies are listed as Restrictions
in the command's documentation.
</P>
<P>Initialization:
</P>
<P><A HREF = "atom_modify.html">atom_modify</A>, <A HREF = "atom_style.html">atom_style</A>,
<A HREF = "boundary.html">boundary</A>, <A HREF = "dimension.html">dimension</A>,
<A HREF = "newton.html">newton</A>, <A HREF = "processors.html">processors</A>, <A HREF = "units.html">units</A>
</P>
<P>Atom definition:
</P>
<P><A HREF = "create_atoms.html">create_atoms</A>, <A HREF = "create_box.html">create_box</A>,
<A HREF = "lattice.html">lattice</A>, <A HREF = "read_data.html">read_data</A>,
<A HREF = "read_restart.html">read_restart</A>, <A HREF = "region.html">region</A>,
<A HREF = "replicate.html">replicate</A>
</P>
<P>Force fields:
</P>
<P><A HREF = "angle_coeff.html">angle_coeff</A>, <A HREF = "angle_style.html">angle_style</A>,
<A HREF = "bond_coeff.html">bond_coeff</A>, <A HREF = "bond_style.html">bond_style</A>,
<A HREF = "dielectric.html">dielectric</A>, <A HREF = "dihedral_coeff.html">dihedral_coeff</A>,
<A HREF = "dihedral_style.html">dihedral_style</A>,
<A HREF = "improper_coeff.html">improper_coeff</A>,
<A HREF = "improper_style.html">improper_style</A>,
<A HREF = "kspace_modify.html">kspace_modify</A>, <A HREF = "kspace_style.html">kspace_style</A>,
<A HREF = "pair_coeff.html">pair_coeff</A>, <A HREF = "pair_modify.html">pair_modify</A>,
<A HREF = "pair_style.html">pair_style</A>, <A HREF = "pair_write.html">pair_write</A>,
<A HREF = "special_bonds.html">special_bonds</A>
</P>
<P>Settings:
</P>
<P><A HREF = "communicate.html">communicate</A>, <A HREF = "dipole.html">dipole</A>,
<A HREF = "group.html">group</A>, <A HREF = "mass.html">mass</A>, <A HREF = "min_modify.html">min_modify</A>,
<A HREF = "min_style.html">min_style</A>, <A HREF = "neigh_modify.html">neigh_modify</A>,
<A HREF = "neighbor.html">neighbor</A>, <A HREF = "reset_timestep.html">reset_timestep</A>,
<A HREF = "run_style.html">run_style</A>, <A HREF = "set.html">set</A>, <A HREF = "shape.html">shape</A>,
<A HREF = "timestep.html">timestep</A>, <A HREF = "velocity.html">velocity</A>
</P>
<P>Fixes:
</P>
<P><A HREF = "fix.html">fix</A>, <A HREF = "fix_modify.html">fix_modify</A>, <A HREF = "unfix.html">unfix</A>
</P>
<P>Computes:
</P>
<P><A HREF = "compute.html">compute</A>, <A HREF = "compute_modify.html">compute_modify</A>,
<A HREF = "uncompute.html">uncompute</A>
</P>
<P>Output:
</P>
<P><A HREF = "dump.html">dump</A>, <A HREF = "dump_modify.html">dump_modify</A>,
<A HREF = "restart.html">restart</A>, <A HREF = "thermo.html">thermo</A>,
<A HREF = "thermo_modify.html">thermo_modify</A>, <A HREF = "thermo_style.html">thermo_style</A>,
<A HREF = "undump.html">undump</A>, <A HREF = "write_restart.html">write_restart</A>
</P>
<P>Actions:
</P>
<P><A HREF = "delete_atoms.html">delete_atoms</A>, <A HREF = "delete_bonds.html">delete_bonds</A>,
<A HREF = "displace_atoms.html">displace_atoms</A>,
<A HREF = "displace_box.html">displace_box</A>, <A HREF = "minimize.html">minimize</A>,
<A HREF = "prd.html">prd</A>, <A HREF = "run.html">run</A>, <A HREF = "temper.html">temper</A>
</P>
<P>Miscellaneous:
</P>
<P><A HREF = "clear.html">clear</A>, <A HREF = "echo.html">echo</A>, <A HREF = "if.html">if</A>,
<A HREF = "include.html">include</A>, <A HREF = "jump.html">jump</A>, <A HREF = "label.html">label</A>,
<A HREF = "log.html">log</A>, <A HREF = "next.html">next</A>, <A HREF = "print.html">print</A>,
<A HREF = "shell.html">shell</A>, <A HREF = "variable.html">variable</A>
</P>
<HR>
<H4><A NAME = "3_5"></A><A NAME = "comm"></A>3.5 Individual commands
</H4>
<P>This section lists all LAMMPS commands alphabetically, with a separate
listing below of styles within certain commands. The <A HREF = "#3_4">previous
section</A> lists the same commands, grouped by category. Note that
some style options for some commands are part of specific LAMMPS
packages, which means they cannot be used unless the package was
included when LAMMPS was built. Not all packages are included in a
default LAMMPS build. These dependencies are listed as Restrictions
in the command's documentation.
</P>
<DIV ALIGN=center><TABLE BORDER=1 >
<TR ALIGN="center"><TD ><A HREF = "angle_coeff.html">angle_coeff</A></TD><TD ><A HREF = "angle_style.html">angle_style</A></TD><TD ><A HREF = "atom_modify.html">atom_modify</A></TD><TD ><A HREF = "atom_style.html">atom_style</A></TD><TD ><A HREF = "bond_coeff.html">bond_coeff</A></TD><TD ><A HREF = "bond_style.html">bond_style</A></TD></TR>
<TR ALIGN="center"><TD ><A HREF = "boundary.html">boundary</A></TD><TD ><A HREF = "change_box.html">change_box</A></TD><TD ><A HREF = "clear.html">clear</A></TD><TD ><A HREF = "communicate.html">communicate</A></TD><TD ><A HREF = "compute.html">compute</A></TD><TD ><A HREF = "compute_modify.html">compute_modify</A></TD></TR>
<TR ALIGN="center"><TD ><A HREF = "create_atoms.html">create_atoms</A></TD><TD ><A HREF = "create_box.html">create_box</A></TD><TD ><A HREF = "delete_atoms.html">delete_atoms</A></TD><TD ><A HREF = "delete_bonds.html">delete_bonds</A></TD><TD ><A HREF = "dielectric.html">dielectric</A></TD><TD ><A HREF = "dihedral_coeff.html">dihedral_coeff</A></TD></TR>
<TR ALIGN="center"><TD ><A HREF = "dihedral_style.html">dihedral_style</A></TD><TD ><A HREF = "dimension.html">dimension</A></TD><TD ><A HREF = "dipole.html">dipole</A></TD><TD ><A HREF = "displace_atoms.html">displace_atoms</A></TD><TD ><A HREF = "displace_box.html">displace_box</A></TD><TD ><A HREF = "dump.html">dump</A></TD></TR>
<TR ALIGN="center"><TD ><A HREF = "dump_modify.html">dump_modify</A></TD><TD ><A HREF = "echo.html">echo</A></TD><TD ><A HREF = "fix.html">fix</A></TD><TD ><A HREF = "fix_modify.html">fix_modify</A></TD><TD ><A HREF = "group.html">group</A></TD><TD ><A HREF = "if.html">if</A></TD></TR>
<TR ALIGN="center"><TD ><A HREF = "improper_coeff.html">improper_coeff</A></TD><TD ><A HREF = "improper_style.html">improper_style</A></TD><TD ><A HREF = "include.html">include</A></TD><TD ><A HREF = "jump.html">jump</A></TD><TD ><A HREF = "kspace_modify.html">kspace_modify</A></TD><TD ><A HREF = "kspace_style.html">kspace_style</A></TD></TR>
<TR ALIGN="center"><TD ><A HREF = "label.html">label</A></TD><TD ><A HREF = "lattice.html">lattice</A></TD><TD ><A HREF = "log.html">log</A></TD><TD ><A HREF = "mass.html">mass</A></TD><TD ><A HREF = "minimize.html">minimize</A></TD><TD ><A HREF = "min_modify.html">min_modify</A></TD></TR>
<TR ALIGN="center"><TD ><A HREF = "min_style.html">min_style</A></TD><TD ><A HREF = "neigh_modify.html">neigh_modify</A></TD><TD ><A HREF = "neighbor.html">neighbor</A></TD><TD ><A HREF = "newton.html">newton</A></TD><TD ><A HREF = "next.html">next</A></TD><TD ><A HREF = "pair_coeff.html">pair_coeff</A></TD></TR>
<TR ALIGN="center"><TD ><A HREF = "pair_modify.html">pair_modify</A></TD><TD ><A HREF = "pair_style.html">pair_style</A></TD><TD ><A HREF = "pair_write.html">pair_write</A></TD><TD ><A HREF = "prd.html">prd</A></TD><TD ><A HREF = "print.html">print</A></TD><TD ><A HREF = "processors.html">processors</A></TD></TR>
<TR ALIGN="center"><TD ><A HREF = "read_data.html">read_data</A></TD><TD ><A HREF = "read_restart.html">read_restart</A></TD><TD ><A HREF = "region.html">region</A></TD><TD ><A HREF = "replicate.html">replicate</A></TD><TD ><A HREF = "reset_timestep.html">reset_timestep</A></TD><TD ><A HREF = "restart.html">restart</A></TD></TR>
<TR ALIGN="center"><TD ><A HREF = "run.html">run</A></TD><TD ><A HREF = "run_style.html">run_style</A></TD><TD ><A HREF = "set.html">set</A></TD><TD ><A HREF = "shape.html">shape</A></TD><TD ><A HREF = "shell.html">shell</A></TD><TD ><A HREF = "special_bonds.html">special_bonds</A></TD></TR>
<TR ALIGN="center"><TD ><A HREF = "temper.html">temper</A></TD><TD ><A HREF = "thermo.html">thermo</A></TD><TD ><A HREF = "thermo_modify.html">thermo_modify</A></TD><TD ><A HREF = "thermo_style.html">thermo_style</A></TD><TD ><A HREF = "timestep.html">timestep</A></TD><TD ><A HREF = "uncompute.html">uncompute</A></TD></TR>
<TR ALIGN="center"><TD ><A HREF = "undump.html">undump</A></TD><TD ><A HREF = "unfix.html">unfix</A></TD><TD ><A HREF = "units.html">units</A></TD><TD ><A HREF = "variable.html">variable</A></TD><TD ><A HREF = "velocity.html">velocity</A></TD><TD ><A HREF = "write_restart.html">write_restart</A>
</TD></TR></TABLE></DIV>
<HR>
<H4>Fix styles
</H4>
<P>See the <A HREF = "fix.html">fix</A> command for one-line descriptions
of each style or click on the style itself for a full description:
</P>
<DIV ALIGN=center><TABLE BORDER=1 >
<TR ALIGN="center"><TD ><A HREF = "fix_addforce.html">addforce</A></TD><TD ><A HREF = "fix_aveforce.html">aveforce</A></TD><TD ><A HREF = "fix_ave_atom.html">ave/atom</A></TD><TD ><A HREF = "fix_ave_histo.html">ave/histo</A></TD><TD ><A HREF = "fix_ave_spatial.html">ave/spatial</A></TD><TD ><A HREF = "fix_ave_time.html">ave/time</A></TD><TD ><A HREF = "fix_bond_break.html">bond/break</A></TD><TD ><A HREF = "fix_bond_create.html">bond/create</A></TD></TR>
<TR ALIGN="center"><TD ><A HREF = "fix_bond_swap.html">bond/swap</A></TD><TD ><A HREF = "fix_box_relax.html">box/relax</A></TD><TD ><A HREF = "fix_deform.html">deform</A></TD><TD ><A HREF = "fix_deposit.html">deposit</A></TD><TD ><A HREF = "fix_drag.html">drag</A></TD><TD ><A HREF = "fix_dt_reset.html">dt/reset</A></TD><TD ><A HREF = "fix_efield.html">efield</A></TD><TD ><A HREF = "fix_enforce2d.html">enforce2d</A></TD></TR>
<TR ALIGN="center"><TD ><A HREF = "fix_evaporate.html">evaporate</A></TD><TD ><A HREF = "fix_freeze.html">freeze</A></TD><TD ><A HREF = "fix_gravity.html">gravity</A></TD><TD ><A HREF = "fix_heat.html">heat</A></TD><TD ><A HREF = "fix_indent.html">indent</A></TD><TD ><A HREF = "fix_langevin.html">langevin</A></TD><TD ><A HREF = "fix_lineforce.html">lineforce</A></TD><TD ><A HREF = "fix_momentum.html">momentum</A></TD></TR>
<TR ALIGN="center"><TD ><A HREF = "fix_move.html">move</A></TD><TD ><A HREF = "fix_nh.html">nph</A></TD><TD ><A HREF = "fix_nph_asphere.html">nph/asphere</A></TD><TD ><A HREF = "fix_nph_sphere.html">nph/sphere</A></TD><TD ><A HREF = "fix_nh.html">npt</A></TD><TD ><A HREF = "fix_npt_asphere.html">npt/asphere</A></TD><TD ><A HREF = "fix_npt_sphere.html">npt/sphere</A></TD><TD ><A HREF = "fix_nve.html">nve</A></TD></TR>
<TR ALIGN="center"><TD ><A HREF = "fix_nve_asphere.html">nve/asphere</A></TD><TD ><A HREF = "fix_nve_limit.html">nve/limit</A></TD><TD ><A HREF = "fix_nve_noforce.html">nve/noforce</A></TD><TD ><A HREF = "fix_nve_sphere.html">nve/sphere</A></TD><TD ><A HREF = "fix_nh.html">nvt</A></TD><TD ><A HREF = "fix_nvt_asphere.html">nvt/asphere</A></TD><TD ><A HREF = "fix_nvt_sllod.html">nvt/sllod</A></TD><TD ><A HREF = "fix_nvt_sphere.html">nvt/sphere</A></TD></TR>
<TR ALIGN="center"><TD ><A HREF = "fix_orient_fcc.html">orient/fcc</A></TD><TD ><A HREF = "fix_planeforce.html">planeforce</A></TD><TD ><A HREF = "fix_poems.html">poems</A></TD><TD ><A HREF = "fix_pour.html">pour</A></TD><TD ><A HREF = "fix_press_berendsen.html">press/berendsen</A></TD><TD ><A HREF = "fix_print.html">print</A></TD><TD ><A HREF = "fix_reax_bonds.html">reax/bonds</A></TD><TD ><A HREF = "fix_recenter.html">recenter</A></TD></TR>
<TR ALIGN="center"><TD ><A HREF = "fix_rigid.html">rigid</A></TD><TD ><A HREF = "fix_rigid.html">rigid/nve</A></TD><TD ><A HREF = "fix_rigid.html">rigid/nvt</A></TD><TD ><A HREF = "fix_setforce.html">setforce</A></TD><TD ><A HREF = "fix_shake.html">shake</A></TD><TD ><A HREF = "fix_spring.html">spring</A></TD><TD ><A HREF = "fix_spring_rg.html">spring/rg</A></TD><TD ><A HREF = "fix_spring_self.html">spring/self</A></TD></TR>
<TR ALIGN="center"><TD ><A HREF = "fix_store_coord.html">store/coord</A></TD><TD ><A HREF = "fix_store_force.html">store/force</A></TD><TD ><A HREF = "fix_temp_berendsen.html">temp/berendsen</A></TD><TD ><A HREF = "fix_temp_rescale.html">temp/rescale</A></TD><TD ><A HREF = "fix_thermal_conductivity.html">thermal/conductivity</A></TD><TD ><A HREF = "fix_tmd.html">tmd</A></TD><TD ><A HREF = "fix_ttm.html">ttm</A></TD><TD ><A HREF = "fix_viscosity.html">viscosity</A></TD></TR>
<TR ALIGN="center"><TD ><A HREF = "fix_viscous.html">viscous</A></TD><TD ><A HREF = "fix_wall.html">wall/colloid</A></TD><TD ><A HREF = "fix_wall_gran.html">wall/gran</A></TD><TD ><A HREF = "fix_wall.html">wall/harmonic</A></TD><TD ><A HREF = "fix_wall.html">wall/lj126</A></TD><TD ><A HREF = "fix_wall.html">wall/lj93</A></TD><TD ><A HREF = "fix_wall_reflect.html">wall/reflect</A></TD><TD ><A HREF = "fix_wall_region.html">wall/region</A>
</TD></TR></TABLE></DIV>
<P>These are fix styles contributed by users, which can be used if
<A HREF = "Section_start.html#2_3">LAMMPS is built with the appropriate package</A>.
</P>
<DIV ALIGN=center><TABLE BORDER=1 >
<TR ALIGN="center"><TD ><A HREF = "fix_atc.html">atc</A></TD><TD ><A HREF = "fix_imd.html">imd</A></TD><TD ><A HREF = "fix_smd.html">smd</A>
</TD></TR></TABLE></DIV>
<HR>
<H4>Compute styles
</H4>
<P>See the <A HREF = "compute.html">compute</A> command for one-line descriptions of
each style or click on the style itself for a full description:
</P>
<DIV ALIGN=center><TABLE BORDER=1 >
<TR ALIGN="center"><TD ><A HREF = "compute_angle_local.html">angle/local</A></TD><TD ><A HREF = "compute_bond_local.html">bond/local</A></TD><TD ><A HREF = "compute_centro_atom.html">centro/atom</A></TD><TD ><A HREF = "compute_cna_atom.html">cna/atom</A></TD><TD ><A HREF = "compute_com.html">com</A></TD><TD ><A HREF = "compute_com_molecule.html">com/molecule</A></TD></TR>
<TR ALIGN="center"><TD ><A HREF = "compute_coord_atom.html">coord/atom</A></TD><TD ><A HREF = "compute_damage_atom.html">damage/atom</A></TD><TD ><A HREF = "compute_dihedral_local.html">dihedral/local</A></TD><TD ><A HREF = "compute_displace_atom.html">displace/atom</A></TD><TD ><A HREF = "compute_erotate_asphere.html">erotate/asphere</A></TD><TD ><A HREF = "compute_erotate_sphere.html">erotate/sphere</A></TD></TR>
<TR ALIGN="center"><TD ><A HREF = "compute_event_displace.html">event/displace</A></TD><TD ><A HREF = "compute_group_group.html">group/group</A></TD><TD ><A HREF = "compute_gyration.html">gyration</A></TD><TD ><A HREF = "compute_gyration_molecule.html">gyration/molecule</A></TD><TD ><A HREF = "compute_heat_flux.html">heat/flux</A></TD><TD ><A HREF = "compute_improper_local.html">improper/local</A></TD></TR>
<TR ALIGN="center"><TD ><A HREF = "compute_ke.html">ke</A></TD><TD ><A HREF = "compute_ke_atom.html">ke/atom</A></TD><TD ><A HREF = "compute_msd.html">msd</A></TD><TD ><A HREF = "compute_msd_molecule.html">msd/molecule</A></TD><TD ><A HREF = "compute_pair_local.html">pair/local</A></TD><TD ><A HREF = "compute_pe.html">pe</A></TD></TR>
<TR ALIGN="center"><TD ><A HREF = "compute_pe_atom.html">pe/atom</A></TD><TD ><A HREF = "compute_pressure.html">pressure</A></TD><TD ><A HREF = "compute_property_atom.html">property/atom</A></TD><TD ><A HREF = "compute_property_local.html">property/local</A></TD><TD ><A HREF = "compute_property_molecule.html">property/molecule</A></TD><TD ><A HREF = "compute_rdf.html">rdf</A></TD></TR>
<TR ALIGN="center"><TD ><A HREF = "compute_reduce.html">reduce</A></TD><TD ><A HREF = "compute_reduce.html">reduce/region</A></TD><TD ><A HREF = "compute_stress_atom.html">stress/atom</A></TD><TD ><A HREF = "compute_temp.html">temp</A></TD><TD ><A HREF = "compute_temp_asphere.html">temp/asphere</A></TD><TD ><A HREF = "compute_temp_com.html">temp/com</A></TD></TR>
<TR ALIGN="center"><TD ><A HREF = "compute_temp_deform.html">temp/deform</A></TD><TD ><A HREF = "compute_temp_partial.html">temp/partial</A></TD><TD ><A HREF = "compute_temp_profile.html">temp/profile</A></TD><TD ><A HREF = "compute_temp_ramp.html">temp/ramp</A></TD><TD ><A HREF = "compute_temp_region.html">temp/region</A></TD><TD ><A HREF = "compute_temp_sphere.html">temp/sphere</A>
</TD></TR></TABLE></DIV>
<P>These are compute styles contributed by users, which can be used if
<A HREF = "Section_start.html#2_3">LAMMPS is built with the appropriate package</A>.
</P>
<DIV ALIGN=center><TABLE BORDER=1 >
<TR ALIGN="center"><TD ><A HREF = "compute_ackland_atom.html">ackland/atom</A>
</TD></TR></TABLE></DIV>
<HR>
<H4>Pair_style potentials
</H4>
<P>See the <A HREF = "pair_style.html">pair_style</A> command for an overview of pair
potentials. Click on the style itself for a full description:
</P>
<DIV ALIGN=center><TABLE BORDER=1 >
<TR ALIGN="center"><TD ><A HREF = "pair_none.html">none</A></TD><TD ><A HREF = "pair_hybrid.html">hybrid</A></TD><TD ><A HREF = "pair_hybrid.html">hybrid/overlay</A></TD><TD ><A HREF = "pair_airebo.html">airebo</A></TD></TR>
<TR ALIGN="center"><TD ><A HREF = "pair_born.html">born/coul/long</A></TD><TD ><A HREF = "pair_buck.html">buck</A></TD><TD ><A HREF = "pair_buck.html">buck/coul/cut</A></TD><TD ><A HREF = "pair_buck.html">buck/coul/long</A></TD></TR>
<TR ALIGN="center"><TD ><A HREF = "pair_colloid.html">colloid</A></TD><TD ><A HREF = "pair_coul.html">coul/cut</A></TD><TD ><A HREF = "pair_coul.html">coul/debye</A></TD><TD ><A HREF = "pair_coul.html">coul/long</A></TD></TR>
-<TR ALIGN="center"><TD ><A HREF = "pair_dipole.html">dipole/cut</A></TD><TD ><A HREF = "pair_dpd.html">dpd</A></TD><TD ><A HREF = "pair_dsmc.html">dsmc</A></TD><TD ><A HREF = "pair_eam.html">eam</A></TD></TR>
-<TR ALIGN="center"><TD ><A HREF = "pair_eam.html">eam/opt</A></TD><TD ><A HREF = "pair_eam.html">eam/alloy</A></TD><TD ><A HREF = "pair_eam.html">eam/alloy/opt</A></TD><TD ><A HREF = "pair_eam.html">eam/fs</A></TD></TR>
-<TR ALIGN="center"><TD ><A HREF = "pair_eam.html">eam/fs/opt</A></TD><TD ><A HREF = "pair_gayberne.html">gayberne</A></TD><TD ><A HREF = "pair_gayberne.html">gayberne/gpu</A></TD><TD ><A HREF = "pair_gran.html">gran/hertz/history</A></TD></TR>
-<TR ALIGN="center"><TD ><A HREF = "pair_gran.html">gran/hooke</A></TD><TD ><A HREF = "pair_gran.html">gran/hooke/history</A></TD><TD ><A HREF = "pair_charmm.html">lj/charmm/coul/charmm</A></TD><TD ><A HREF = "pair_charmm.html">lj/charmm/coul/charmm/implicit</A></TD></TR>
-<TR ALIGN="center"><TD ><A HREF = "pair_charmm.html">lj/charmm/coul/long</A></TD><TD ><A HREF = "pair_charmm.html">lj/charmm/coul/long/opt</A></TD><TD ><A HREF = "pair_class2.html">lj/class2</A></TD><TD ><A HREF = "pair_class2.html">lj/class2/coul/cut</A></TD></TR>
-<TR ALIGN="center"><TD ><A HREF = "pair_class2.html">lj/class2/coul/long</A></TD><TD ><A HREF = "pair_lj.html">lj/cut</A></TD><TD ><A HREF = "pair_lj.html">lj/cut/gpu</A></TD><TD ><A HREF = "pair_lj.html">lj/cut/opt</A></TD></TR>
-<TR ALIGN="center"><TD ><A HREF = "pair_lj.html">lj/cut/coul/cut</A></TD><TD ><A HREF = "pair_lj.html">lj/cut/coul/debye</A></TD><TD ><A HREF = "pair_lj.html">lj/cut/coul/long</A></TD><TD ><A HREF = "pair_lj.html">lj/cut/coul/long/tip4p</A></TD></TR>
-<TR ALIGN="center"><TD ><A HREF = "pair_lj_expand.html">lj/expand</A></TD><TD ><A HREF = "pair_gromacs.html">lj/gromacs</A></TD><TD ><A HREF = "pair_gromacs.html">lj/gromacs/coul/gromacs</A></TD><TD ><A HREF = "pair_lj_smooth.html">lj/smooth</A></TD></TR>
-<TR ALIGN="center"><TD ><A HREF = "pair_lj96_cut.html">lj96/cut</A></TD><TD ><A HREF = "pair_lubricate.html">lubricate</A></TD><TD ><A HREF = "pair_meam.html">meam</A></TD><TD ><A HREF = "pair_morse.html">morse</A></TD></TR>
-<TR ALIGN="center"><TD ><A HREF = "pair_morse.html">morse/opt</A></TD><TD ><A HREF = "pair_peri_pmb.html">peri/pmb</A></TD><TD ><A HREF = "pair_reax.html">reax</A></TD><TD ><A HREF = "pair_resquared.html">resquared</A></TD></TR>
-<TR ALIGN="center"><TD ><A HREF = "pair_soft.html">soft</A></TD><TD ><A HREF = "pair_sw.html">sw</A></TD><TD ><A HREF = "pair_table.html">table</A></TD><TD ><A HREF = "pair_tersoff.html">tersoff</A></TD></TR>
-<TR ALIGN="center"><TD ><A HREF = "pair_tersoff_zbl.html">tersoff/zbl</A></TD><TD ><A HREF = "pair_yukawa.html">yukawa</A></TD><TD ><A HREF = "pair_yukawa_colloid.html">yukawa/colloid</A>
+<TR ALIGN="center"><TD ><A HREF = "pair_dipole.html">dipole/cut</A></TD><TD ><A HREF = "pair_dpd.html">dpd</A></TD><TD ><A HREF = "pair_dpd.html">dpd/tstat</A></TD><TD ><A HREF = "pair_dsmc.html">dsmc</A></TD></TR>
+<TR ALIGN="center"><TD ><A HREF = "pair_eam.html">eam</A></TD><TD ><A HREF = "pair_eam.html">eam/opt</A></TD><TD ><A HREF = "pair_eam.html">eam/alloy</A></TD><TD ><A HREF = "pair_eam.html">eam/alloy/opt</A></TD></TR>
+<TR ALIGN="center"><TD ><A HREF = "pair_eam.html">eam/fs</A></TD><TD ><A HREF = "pair_eam.html">eam/fs/opt</A></TD><TD ><A HREF = "pair_gayberne.html">gayberne</A></TD><TD ><A HREF = "pair_gayberne.html">gayberne/gpu</A></TD></TR>
+<TR ALIGN="center"><TD ><A HREF = "pair_gran.html">gran/hertz/history</A></TD><TD ><A HREF = "pair_gran.html">gran/hooke</A></TD><TD ><A HREF = "pair_gran.html">gran/hooke/history</A></TD><TD ><A HREF = "pair_charmm.html">lj/charmm/coul/charmm</A></TD></TR>
+<TR ALIGN="center"><TD ><A HREF = "pair_charmm.html">lj/charmm/coul/charmm/implicit</A></TD><TD ><A HREF = "pair_charmm.html">lj/charmm/coul/long</A></TD><TD ><A HREF = "pair_charmm.html">lj/charmm/coul/long/opt</A></TD><TD ><A HREF = "pair_class2.html">lj/class2</A></TD></TR>
+<TR ALIGN="center"><TD ><A HREF = "pair_class2.html">lj/class2/coul/cut</A></TD><TD ><A HREF = "pair_class2.html">lj/class2/coul/long</A></TD><TD ><A HREF = "pair_lj.html">lj/cut</A></TD><TD ><A HREF = "pair_lj.html">lj/cut/gpu</A></TD></TR>
+<TR ALIGN="center"><TD ><A HREF = "pair_lj.html">lj/cut/opt</A></TD><TD ><A HREF = "pair_lj.html">lj/cut/coul/cut</A></TD><TD ><A HREF = "pair_lj.html">lj/cut/coul/debye</A></TD><TD ><A HREF = "pair_lj.html">lj/cut/coul/long</A></TD></TR>
+<TR ALIGN="center"><TD ><A HREF = "pair_lj.html">lj/cut/coul/long/tip4p</A></TD><TD ><A HREF = "pair_lj_expand.html">lj/expand</A></TD><TD ><A HREF = "pair_gromacs.html">lj/gromacs</A></TD><TD ><A HREF = "pair_gromacs.html">lj/gromacs/coul/gromacs</A></TD></TR>
+<TR ALIGN="center"><TD ><A HREF = "pair_lj_smooth.html">lj/smooth</A></TD><TD ><A HREF = "pair_lj96_cut.html">lj96/cut</A></TD><TD ><A HREF = "pair_lubricate.html">lubricate</A></TD><TD ><A HREF = "pair_meam.html">meam</A></TD></TR>
+<TR ALIGN="center"><TD ><A HREF = "pair_morse.html">morse</A></TD><TD ><A HREF = "pair_morse.html">morse/opt</A></TD><TD ><A HREF = "pair_peri_pmb.html">peri/pmb</A></TD><TD ><A HREF = "pair_reax.html">reax</A></TD></TR>
+<TR ALIGN="center"><TD ><A HREF = "pair_resquared.html">resquared</A></TD><TD ><A HREF = "pair_soft.html">soft</A></TD><TD ><A HREF = "pair_sw.html">sw</A></TD><TD ><A HREF = "pair_table.html">table</A></TD></TR>
+<TR ALIGN="center"><TD ><A HREF = "pair_tersoff.html">tersoff</A></TD><TD ><A HREF = "pair_tersoff_zbl.html">tersoff/zbl</A></TD><TD ><A HREF = "pair_yukawa.html">yukawa</A></TD><TD ><A HREF = "pair_yukawa_colloid.html">yukawa/colloid</A>
</TD></TR></TABLE></DIV>
<P>These are pair styles contributed by users, which can be used if
<A HREF = "Section_start.html#2_3">LAMMPS is built with the appropriate package</A>.
</P>
<DIV ALIGN=center><TABLE BORDER=1 >
<TR ALIGN="center"><TD ><A HREF = "pair_buck_coul.html">buck/coul</A></TD><TD ><A HREF = "pair_cmm.html">cg/cmm</A></TD><TD ><A HREF = "pair_cmm.html">cg/cmm/coul/cut</A></TD><TD ><A HREF = "pair_cmm.html">cg/cmm/coul/long</A></TD></TR>
<TR ALIGN="center"><TD ><A HREF = "pair_eam.html">eam/cd</A></TD><TD ><A HREF = "pair_lj_coul.html">lj/coul</A>
</TD></TR></TABLE></DIV>
<HR>
<H4>Bond_style potentials
</H4>
<P>See the <A HREF = "bond_style.html">bond_style</A> command for an overview of bond
potentials. Click on the style itself for a full description:
</P>
<DIV ALIGN=center><TABLE BORDER=1 >
<TR ALIGN="center"><TD WIDTH="100"><A HREF = "bond_none.html">none</A></TD><TD WIDTH="100"><A HREF = "bond_hybrid.html">hybrid</A></TD><TD WIDTH="100"><A HREF = "bond_class2.html">class2</A></TD><TD WIDTH="100"><A HREF = "bond_fene.html">fene</A></TD></TR>
<TR ALIGN="center"><TD WIDTH="100"><A HREF = "bond_fene_expand.html">fene/expand</A></TD><TD WIDTH="100"><A HREF = "bond_harmonic.html">harmonic</A></TD><TD WIDTH="100"><A HREF = "bond_morse.html">morse</A></TD><TD WIDTH="100"><A HREF = "bond_nonlinear.html">nonlinear</A></TD></TR>
<TR ALIGN="center"><TD WIDTH="100"><A HREF = "bond_quartic.html">quartic</A></TD><TD WIDTH="100"><A HREF = "bond_table.html">table</A>
</TD></TR></TABLE></DIV>
<HR>
<H4>Angle_style potentials
</H4>
<P>See the <A HREF = "angle_style.html">angle_style</A> command for an overview of
angle potentials. Click on the style itself for a full description:
</P>
<DIV ALIGN=center><TABLE BORDER=1 >
<TR ALIGN="center"><TD WIDTH="100"><A HREF = "angle_none.html">none</A></TD><TD WIDTH="100"><A HREF = "angle_hybrid.html">hybrid</A></TD><TD WIDTH="100"><A HREF = "angle_charmm.html">charmm</A></TD><TD WIDTH="100"><A HREF = "angle_class2.html">class2</A></TD></TR>
<TR ALIGN="center"><TD WIDTH="100"><A HREF = "angle_cosine.html">cosine</A></TD><TD WIDTH="100"><A HREF = "angle_cosine_delta.html">cosine/delta</A></TD><TD WIDTH="100"><A HREF = "angle_cosine_squared.html">cosine/squared</A></TD><TD WIDTH="100"><A HREF = "angle_harmonic.html">harmonic</A></TD></TR>
<TR ALIGN="center"><TD WIDTH="100"><A HREF = "angle_table.html">table</A>
</TD></TR></TABLE></DIV>
<P>These are angle styles contributed by users, which can be used if
<A HREF = "Section_start.html#2_3">LAMMPS is built with the appropriate package</A>.
</P>
<DIV ALIGN=center><TABLE BORDER=1 >
<TR ALIGN="center"><TD ><A HREF = "angle_cmm.html">cg/cmm</A>
</TD></TR></TABLE></DIV>
<HR>
<H4>Dihedral_style potentials
</H4>
<P>See the <A HREF = "dihedral_style.html">dihedral_style</A> command for an overview
of dihedral potentials. Click on the style itself for a full
description:
</P>
<DIV ALIGN=center><TABLE BORDER=1 >
<TR ALIGN="center"><TD WIDTH="100"><A HREF = "dihedral_none.html">none</A></TD><TD WIDTH="100"><A HREF = "dihedral_hybrid.html">hybrid</A></TD><TD WIDTH="100"><A HREF = "dihedral_charmm.html">charmm</A></TD><TD WIDTH="100"><A HREF = "dihedral_class2.html">class2</A></TD></TR>
<TR ALIGN="center"><TD WIDTH="100"><A HREF = "dihedral_harmonic.html">harmonic</A></TD><TD WIDTH="100"><A HREF = "dihedral_helix.html">helix</A></TD><TD WIDTH="100"><A HREF = "dihedral_multi_harmonic.html">multi/harmonic</A></TD><TD WIDTH="100"><A HREF = "dihedral_opls.html">opls</A>
</TD></TR></TABLE></DIV>
<HR>
<H4>Improper_style potentials
</H4>
<P>See the <A HREF = "improper_style.html">improper_style</A> command for an overview
of improper potentials. Click on the style itself for a full
description:
</P>
<DIV ALIGN=center><TABLE BORDER=1 >
<TR ALIGN="center"><TD WIDTH="100"><A HREF = "improper_none.html">none</A></TD><TD WIDTH="100"><A HREF = "improper_hybrid.html">hybrid</A></TD><TD WIDTH="100"><A HREF = "improper_class2.html">class2</A></TD><TD WIDTH="100"><A HREF = "improper_cvff.html">cvff</A></TD></TR>
<TR ALIGN="center"><TD WIDTH="100"><A HREF = "improper_harmonic.html">harmonic</A>
</TD></TR></TABLE></DIV>
<HR>
<H4>Kspace solvers
</H4>
<P>See the <A HREF = "kspace_style.html">kspace_style</A> command for an overview of
Kspace solvers. Click on the style itself for a full description:
</P>
<DIV ALIGN=center><TABLE BORDER=1 >
<TR ALIGN="center"><TD WIDTH="100"><A HREF = "kspace_style.html">ewald</A></TD><TD WIDTH="100"><A HREF = "kspace_style.html">pppm</A></TD><TD WIDTH="100"><A HREF = "kspace_style.html">pppm/tip4p</A>
</TD></TR></TABLE></DIV>
<P>These are Kspace solvers contributed by users, which can be used if
<A HREF = "Section_start.html#2_3">LAMMPS is built with the appropriate package</A>.
</P>
<DIV ALIGN=center><TABLE BORDER=1 >
<TR ALIGN="center"><TD WIDTH="100"><A HREF = "kspace_style.html">ewald/n</A>
</TD></TR></TABLE></DIV>
</HTML>
diff --git a/doc/Section_commands.txt b/doc/Section_commands.txt
index 5ec161e04..821e23e9c 100644
--- a/doc/Section_commands.txt
+++ b/doc/Section_commands.txt
@@ -1,682 +1,683 @@
"Previous Section"_Section_start.html - "LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc - "Next Section"_Section_howto.html :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Section_commands.html#comm)
:line
3. Commands :h3
This section describes how a LAMMPS input script is formatted and what
commands are used to define a LAMMPS simulation.
3.1 "LAMMPS input script"_#3_1
3.2 "Parsing rules"_#3_2
3.3 "Input script structure"_#3_3
3.4 "Commands listed by category"_#3_4
3.5 "Commands listed alphabetically"_#3_5 :all(b)
:line
3.1 LAMMPS input script :link(3_1),h4
LAMMPS executes by reading commands from a input script (text file),
one line at a time. When the input script ends, LAMMPS exits. Each
command causes LAMMPS to take some action. It may set an internal
variable, read in a file, or run a simulation. Most commands have
default settings, which means you only need to use the command if you
wish to change the default.
In many cases, the ordering of commands in an input script is not
important. However the following rules apply:
(1) LAMMPS does not read your entire input script and then perform a
simulation with all the settings. Rather, the input script is read
one line at a time and each command takes effect when it is read.
Thus this sequence of commands:
timestep 0.5
run 100
run 100 :pre
does something different than this sequence:
run 100
timestep 0.5
run 100 :pre
In the first case, the specified timestep (0.5 fmsec) is used for two
simulations of 100 timesteps each. In the 2nd case, the default
timestep (1.0 fmsec) is used for the 1st 100 step simulation and a 0.5
fmsec timestep is used for the 2nd one.
(2) Some commands are only valid when they follow other commands. For
example you cannot set the temperature of a group of atoms until atoms
have been defined and a group command is used to define which atoms
belong to the group.
(3) Sometimes command B will use values that can be set by command A.
This means command A must precede command B in the input script if it
is to have the desired effect. For example, the
"read_data"_read_data.html command initializes the system by setting
up the simulation box and assigning atoms to processors. If default
values are not desired, the "processors"_processors.html and
"boundary"_boundary.html commands need to be used before read_data to
tell LAMMPS how to map processors to the simulation box.
Many input script errors are detected by LAMMPS and an ERROR or
WARNING message is printed. "This section"_Section_errors.html gives
more information on what errors mean. The documentation for each
command lists restrictions on how the command can be used.
:line
3.2 Parsing rules :link(3_2),h4
Each non-blank line in the input script is treated as a command.
LAMMPS commands are case sensitive. Command names are lower-case, as
are specified command arguments. Upper case letters may be used in
file names or user-chosen ID strings.
Here is how each line in the input script is parsed by LAMMPS:
(1) If the last printable character on the line is a "&" character
(with no surrounding quotes), the command is assumed to continue on
the next line. The next line is concatenated to the previous line by
removing the "&" character and newline. This allows long commands to
be continued across two or more lines.
(2) All characters from the first "#" character onward are treated as
comment and discarded. See an exception in (6). Note that a
comment after a trailing "&" character will prevent the command from
continuing on the next line. Also note that for multi-line commands a
single leading "#" will comment out the entire command.
(3) The line is searched repeatedly for $ characters, which indicate
variables that are replaced with a text string. See an exception in
(6). If the $ is followed by curly brackets, then the variable name
is the text inside the curly brackets. If no curly brackets follow
the $, then the variable name is the single character immediately
following the $. Thus $\{myTemp\} and $x refer to variable names
"myTemp" and "x". See the "variable"_variable.html command for
details of how strings are assigned to variables and how they are
substituted for in input script commands.
(4) The line is broken into "words" separated by whitespace (tabs,
spaces). Note that words can thus contain letters, digits,
underscores, or punctuation characters.
(5) The first word is the command name. All successive words in the
line are arguments.
(6) If you want text with spaces to be treated as a single argument,
it can be enclosed in double quotes. The quotes are removed when the
single argument is stored in its final form. See the "dump modify
format"_dump_modify.html or "if"_if.html commands for examples. A "#"
or "$" character that is between double quotes will not be treated as
a comment indicator in (2) or substituted for as a variable in (3).
:line
3.3 Input script structure :h4,link(3_3)
This section describes the structure of a typical LAMMPS input script.
The "examples" directory in the LAMMPS distribution contains many
sample input scripts; the corresponding problems are discussed in
"this section"_Section_example.html, and animated on the "LAMMPS WWW
Site"_lws.
A LAMMPS input script typically has 4 parts:
Initialization
Atom definition
Settings
Run a simulation :ol
The last 2 parts can be repeated as many times as desired. I.e. run a
simulation, change some settings, run some more, etc. Each of the 4
parts is now described in more detail. Remember that almost all the
commands need only be used if a non-default value is desired.
(1) Initialization
Set parameters that need to be defined before atoms are created or
read-in from a file.
The relevant commands are "units"_units.html,
"dimension"_dimension.html, "newton"_newton.html,
"processors"_processors.html, "boundary"_boundary.html,
"atom_style"_atom_style.html, "atom_modify"_atom_modify.html.
If force-field parameters appear in the files that will be read, these
commands tell LAMMPS what kinds of force fields are being used:
"pair_style"_pair_style.html, "bond_style"_bond_style.html,
"angle_style"_angle_style.html, "dihedral_style"_dihedral_style.html,
"improper_style"_improper_style.html.
(2) Atom definition
There are 3 ways to define atoms in LAMMPS. Read them in from a data
or restart file via the "read_data"_read_data.html or
"read_restart"_read_restart.html commands. These files can contain
molecular topology information. Or create atoms on a lattice (with no
molecular topology), using these commands: "lattice"_lattice.html,
"region"_region.html, "create_box"_create_box.html,
"create_atoms"_create_atoms.html. The entire set of atoms can be
duplicated to make a larger simulation using the
"replicate"_replicate.html command.
(3) Settings
Once atoms and molecular topology are defined, a variety of settings
can be specified: force field coefficients, simulation parameters,
output options, etc.
Force field coefficients are set by these commands (they can also be
set in the read-in files): "pair_coeff"_pair_coeff.html,
"bond_coeff"_bond_coeff.html, "angle_coeff"_angle_coeff.html,
"dihedral_coeff"_dihedral_coeff.html,
"improper_coeff"_improper_coeff.html,
"kspace_style"_kspace_style.html, "dielectric"_dielectric.html,
"special_bonds"_special_bonds.html.
Various simulation parameters are set by these commands:
"neighbor"_neighbor.html, "neigh_modify"_neigh_modify.html,
"group"_group.html, "timestep"_timestep.html,
"reset_timestep"_reset_timestep.html, "run_style"_run_style.html,
"min_style"_min_style.html, "min_modify"_min_modify.html.
Fixes impose a variety of boundary conditions, time integration, and
diagnostic options. The "fix"_fix.html command comes in many flavors.
Various computations can be specified for execution during a
simulation using the "compute"_compute.html,
"compute_modify"_compute_modify.html, and "variable"_variable.html
commands.
Output options are set by the "thermo"_thermo.html, "dump"_dump.html,
and "restart"_restart.html commands.
(4) Run a simulation
A molecular dynamics simulation is run using the "run"_run.html
command. Energy minimization (molecular statics) is performed using
the "minimize"_minimize.html command. A parallel tempering
(replica-exchange) simulation can be run using the
"temper"_temper.html command.
:line
3.4 Commands listed by category :link(3_4),h4
This section lists all LAMMPS commands, grouped by category. The
"next section"_#3_5 lists the same commands alphabetically. Note that
some style options for some commands are part of specific LAMMPS
packages, which means they cannot be used unless the package was
included when LAMMPS was built. Not all packages are included in a
default LAMMPS build. These dependencies are listed as Restrictions
in the command's documentation.
Initialization:
"atom_modify"_atom_modify.html, "atom_style"_atom_style.html,
"boundary"_boundary.html, "dimension"_dimension.html,
"newton"_newton.html, "processors"_processors.html, "units"_units.html
Atom definition:
"create_atoms"_create_atoms.html, "create_box"_create_box.html,
"lattice"_lattice.html, "read_data"_read_data.html,
"read_restart"_read_restart.html, "region"_region.html,
"replicate"_replicate.html
Force fields:
"angle_coeff"_angle_coeff.html, "angle_style"_angle_style.html,
"bond_coeff"_bond_coeff.html, "bond_style"_bond_style.html,
"dielectric"_dielectric.html, "dihedral_coeff"_dihedral_coeff.html,
"dihedral_style"_dihedral_style.html,
"improper_coeff"_improper_coeff.html,
"improper_style"_improper_style.html,
"kspace_modify"_kspace_modify.html, "kspace_style"_kspace_style.html,
"pair_coeff"_pair_coeff.html, "pair_modify"_pair_modify.html,
"pair_style"_pair_style.html, "pair_write"_pair_write.html,
"special_bonds"_special_bonds.html
Settings:
"communicate"_communicate.html, "dipole"_dipole.html,
"group"_group.html, "mass"_mass.html, "min_modify"_min_modify.html,
"min_style"_min_style.html, "neigh_modify"_neigh_modify.html,
"neighbor"_neighbor.html, "reset_timestep"_reset_timestep.html,
"run_style"_run_style.html, "set"_set.html, "shape"_shape.html,
"timestep"_timestep.html, "velocity"_velocity.html
Fixes:
"fix"_fix.html, "fix_modify"_fix_modify.html, "unfix"_unfix.html
Computes:
"compute"_compute.html, "compute_modify"_compute_modify.html,
"uncompute"_uncompute.html
Output:
"dump"_dump.html, "dump_modify"_dump_modify.html,
"restart"_restart.html, "thermo"_thermo.html,
"thermo_modify"_thermo_modify.html, "thermo_style"_thermo_style.html,
"undump"_undump.html, "write_restart"_write_restart.html
Actions:
"delete_atoms"_delete_atoms.html, "delete_bonds"_delete_bonds.html,
"displace_atoms"_displace_atoms.html,
"displace_box"_displace_box.html, "minimize"_minimize.html,
"prd"_prd.html, "run"_run.html, "temper"_temper.html
Miscellaneous:
"clear"_clear.html, "echo"_echo.html, "if"_if.html,
"include"_include.html, "jump"_jump.html, "label"_label.html,
"log"_log.html, "next"_next.html, "print"_print.html,
"shell"_shell.html, "variable"_variable.html
:line
3.5 Individual commands :h4,link(3_5),link(comm)
This section lists all LAMMPS commands alphabetically, with a separate
listing below of styles within certain commands. The "previous
section"_#3_4 lists the same commands, grouped by category. Note that
some style options for some commands are part of specific LAMMPS
packages, which means they cannot be used unless the package was
included when LAMMPS was built. Not all packages are included in a
default LAMMPS build. These dependencies are listed as Restrictions
in the command's documentation.
"angle_coeff"_angle_coeff.html,
"angle_style"_angle_style.html,
"atom_modify"_atom_modify.html,
"atom_style"_atom_style.html,
"bond_coeff"_bond_coeff.html,
"bond_style"_bond_style.html,
"boundary"_boundary.html,
"change_box"_change_box.html,
"clear"_clear.html,
"communicate"_communicate.html,
"compute"_compute.html,
"compute_modify"_compute_modify.html,
"create_atoms"_create_atoms.html,
"create_box"_create_box.html,
"delete_atoms"_delete_atoms.html,
"delete_bonds"_delete_bonds.html,
"dielectric"_dielectric.html,
"dihedral_coeff"_dihedral_coeff.html,
"dihedral_style"_dihedral_style.html,
"dimension"_dimension.html,
"dipole"_dipole.html,
"displace_atoms"_displace_atoms.html,
"displace_box"_displace_box.html,
"dump"_dump.html,
"dump_modify"_dump_modify.html,
"echo"_echo.html,
"fix"_fix.html,
"fix_modify"_fix_modify.html,
"group"_group.html,
"if"_if.html,
"improper_coeff"_improper_coeff.html,
"improper_style"_improper_style.html,
"include"_include.html,
"jump"_jump.html,
"kspace_modify"_kspace_modify.html,
"kspace_style"_kspace_style.html,
"label"_label.html,
"lattice"_lattice.html,
"log"_log.html,
"mass"_mass.html,
"minimize"_minimize.html,
"min_modify"_min_modify.html,
"min_style"_min_style.html,
"neigh_modify"_neigh_modify.html,
"neighbor"_neighbor.html,
"newton"_newton.html,
"next"_next.html,
"pair_coeff"_pair_coeff.html,
"pair_modify"_pair_modify.html,
"pair_style"_pair_style.html,
"pair_write"_pair_write.html,
"prd"_prd.html,
"print"_print.html,
"processors"_processors.html,
"read_data"_read_data.html,
"read_restart"_read_restart.html,
"region"_region.html,
"replicate"_replicate.html,
"reset_timestep"_reset_timestep.html,
"restart"_restart.html,
"run"_run.html,
"run_style"_run_style.html,
"set"_set.html,
"shape"_shape.html,
"shell"_shell.html,
"special_bonds"_special_bonds.html,
"temper"_temper.html,
"thermo"_thermo.html,
"thermo_modify"_thermo_modify.html,
"thermo_style"_thermo_style.html,
"timestep"_timestep.html,
"uncompute"_uncompute.html,
"undump"_undump.html,
"unfix"_unfix.html,
"units"_units.html,
"variable"_variable.html,
"velocity"_velocity.html,
"write_restart"_write_restart.html :tb(c=6,ea=c)
:line
Fix styles :h4
See the "fix"_fix.html command for one-line descriptions
of each style or click on the style itself for a full description:
"addforce"_fix_addforce.html,
"aveforce"_fix_aveforce.html,
"ave/atom"_fix_ave_atom.html,
"ave/histo"_fix_ave_histo.html,
"ave/spatial"_fix_ave_spatial.html,
"ave/time"_fix_ave_time.html,
"bond/break"_fix_bond_break.html,
"bond/create"_fix_bond_create.html,
"bond/swap"_fix_bond_swap.html,
"box/relax"_fix_box_relax.html,
"deform"_fix_deform.html,
"deposit"_fix_deposit.html,
"drag"_fix_drag.html,
"dt/reset"_fix_dt_reset.html,
"efield"_fix_efield.html,
"enforce2d"_fix_enforce2d.html,
"evaporate"_fix_evaporate.html,
"freeze"_fix_freeze.html,
"gravity"_fix_gravity.html,
"heat"_fix_heat.html,
"indent"_fix_indent.html,
"langevin"_fix_langevin.html,
"lineforce"_fix_lineforce.html,
"momentum"_fix_momentum.html,
"move"_fix_move.html,
"nph"_fix_nh.html,
"nph/asphere"_fix_nph_asphere.html,
"nph/sphere"_fix_nph_sphere.html,
"npt"_fix_nh.html,
"npt/asphere"_fix_npt_asphere.html,
"npt/sphere"_fix_npt_sphere.html,
"nve"_fix_nve.html,
"nve/asphere"_fix_nve_asphere.html,
"nve/limit"_fix_nve_limit.html,
"nve/noforce"_fix_nve_noforce.html,
"nve/sphere"_fix_nve_sphere.html,
"nvt"_fix_nh.html,
"nvt/asphere"_fix_nvt_asphere.html,
"nvt/sllod"_fix_nvt_sllod.html,
"nvt/sphere"_fix_nvt_sphere.html,
"orient/fcc"_fix_orient_fcc.html,
"planeforce"_fix_planeforce.html,
"poems"_fix_poems.html,
"pour"_fix_pour.html,
"press/berendsen"_fix_press_berendsen.html,
"print"_fix_print.html,
"reax/bonds"_fix_reax_bonds.html,
"recenter"_fix_recenter.html,
"rigid"_fix_rigid.html,
"rigid/nve"_fix_rigid.html,
"rigid/nvt"_fix_rigid.html,
"setforce"_fix_setforce.html,
"shake"_fix_shake.html,
"spring"_fix_spring.html,
"spring/rg"_fix_spring_rg.html,
"spring/self"_fix_spring_self.html,
"store/coord"_fix_store_coord.html,
"store/force"_fix_store_force.html,
"temp/berendsen"_fix_temp_berendsen.html,
"temp/rescale"_fix_temp_rescale.html,
"thermal/conductivity"_fix_thermal_conductivity.html,
"tmd"_fix_tmd.html,
"ttm"_fix_ttm.html,
"viscosity"_fix_viscosity.html,
"viscous"_fix_viscous.html,
"wall/colloid"_fix_wall.html,
"wall/gran"_fix_wall_gran.html,
"wall/harmonic"_fix_wall.html,
"wall/lj126"_fix_wall.html,
"wall/lj93"_fix_wall.html,
"wall/reflect"_fix_wall_reflect.html,
"wall/region"_fix_wall_region.html :tb(c=8,ea=c)
These are fix styles contributed by users, which can be used if
"LAMMPS is built with the appropriate package"_Section_start.html#2_3.
"atc"_fix_atc.html,
"imd"_fix_imd.html,
"smd"_fix_smd.html :tb(c=4,ea=c)
:line
Compute styles :h4
See the "compute"_compute.html command for one-line descriptions of
each style or click on the style itself for a full description:
"angle/local"_compute_angle_local.html,
"bond/local"_compute_bond_local.html,
"centro/atom"_compute_centro_atom.html,
"cna/atom"_compute_cna_atom.html,
"com"_compute_com.html,
"com/molecule"_compute_com_molecule.html,
"coord/atom"_compute_coord_atom.html,
"damage/atom"_compute_damage_atom.html,
"dihedral/local"_compute_dihedral_local.html,
"displace/atom"_compute_displace_atom.html,
"erotate/asphere"_compute_erotate_asphere.html,
"erotate/sphere"_compute_erotate_sphere.html,
"event/displace"_compute_event_displace.html,
"group/group"_compute_group_group.html,
"gyration"_compute_gyration.html,
"gyration/molecule"_compute_gyration_molecule.html,
"heat/flux"_compute_heat_flux.html,
"improper/local"_compute_improper_local.html,
"ke"_compute_ke.html,
"ke/atom"_compute_ke_atom.html,
"msd"_compute_msd.html,
"msd/molecule"_compute_msd_molecule.html,
"pair/local"_compute_pair_local.html,
"pe"_compute_pe.html,
"pe/atom"_compute_pe_atom.html,
"pressure"_compute_pressure.html,
"property/atom"_compute_property_atom.html,
"property/local"_compute_property_local.html,
"property/molecule"_compute_property_molecule.html,
"rdf"_compute_rdf.html,
"reduce"_compute_reduce.html,
"reduce/region"_compute_reduce.html,
"stress/atom"_compute_stress_atom.html,
"temp"_compute_temp.html,
"temp/asphere"_compute_temp_asphere.html,
"temp/com"_compute_temp_com.html,
"temp/deform"_compute_temp_deform.html,
"temp/partial"_compute_temp_partial.html,
"temp/profile"_compute_temp_profile.html,
"temp/ramp"_compute_temp_ramp.html,
"temp/region"_compute_temp_region.html,
"temp/sphere"_compute_temp_sphere.html :tb(c=6,ea=c)
These are compute styles contributed by users, which can be used if
"LAMMPS is built with the appropriate package"_Section_start.html#2_3.
"ackland/atom"_compute_ackland_atom.html :tb(c=6,ea=c)
:line
Pair_style potentials :h4
See the "pair_style"_pair_style.html command for an overview of pair
potentials. Click on the style itself for a full description:
"none"_pair_none.html,
"hybrid"_pair_hybrid.html,
"hybrid/overlay"_pair_hybrid.html,
"airebo"_pair_airebo.html,
"born/coul/long"_pair_born.html,
"buck"_pair_buck.html,
"buck/coul/cut"_pair_buck.html,
"buck/coul/long"_pair_buck.html,
"colloid"_pair_colloid.html,
"coul/cut"_pair_coul.html,
"coul/debye"_pair_coul.html,
"coul/long"_pair_coul.html,
"dipole/cut"_pair_dipole.html,
"dpd"_pair_dpd.html,
+"dpd/tstat"_pair_dpd.html,
"dsmc"_pair_dsmc.html,
"eam"_pair_eam.html,
"eam/opt"_pair_eam.html,
"eam/alloy"_pair_eam.html,
"eam/alloy/opt"_pair_eam.html,
"eam/fs"_pair_eam.html,
"eam/fs/opt"_pair_eam.html,
"gayberne"_pair_gayberne.html,
"gayberne/gpu"_pair_gayberne.html,
"gran/hertz/history"_pair_gran.html,
"gran/hooke"_pair_gran.html,
"gran/hooke/history"_pair_gran.html,
"lj/charmm/coul/charmm"_pair_charmm.html,
"lj/charmm/coul/charmm/implicit"_pair_charmm.html,
"lj/charmm/coul/long"_pair_charmm.html,
"lj/charmm/coul/long/opt"_pair_charmm.html,
"lj/class2"_pair_class2.html,
"lj/class2/coul/cut"_pair_class2.html,
"lj/class2/coul/long"_pair_class2.html,
"lj/cut"_pair_lj.html,
"lj/cut/gpu"_pair_lj.html,
"lj/cut/opt"_pair_lj.html,
"lj/cut/coul/cut"_pair_lj.html,
"lj/cut/coul/debye"_pair_lj.html,
"lj/cut/coul/long"_pair_lj.html,
"lj/cut/coul/long/tip4p"_pair_lj.html,
"lj/expand"_pair_lj_expand.html,
"lj/gromacs"_pair_gromacs.html,
"lj/gromacs/coul/gromacs"_pair_gromacs.html,
"lj/smooth"_pair_lj_smooth.html,
"lj96/cut"_pair_lj96_cut.html,
"lubricate"_pair_lubricate.html,
"meam"_pair_meam.html,
"morse"_pair_morse.html,
"morse/opt"_pair_morse.html,
"peri/pmb"_pair_peri_pmb.html,
"reax"_pair_reax.html,
"resquared"_pair_resquared.html,
"soft"_pair_soft.html,
"sw"_pair_sw.html,
"table"_pair_table.html,
"tersoff"_pair_tersoff.html,
"tersoff/zbl"_pair_tersoff_zbl.html,
"yukawa"_pair_yukawa.html,
"yukawa/colloid"_pair_yukawa_colloid.html :tb(c=4,ea=c)
These are pair styles contributed by users, which can be used if
"LAMMPS is built with the appropriate package"_Section_start.html#2_3.
"buck/coul"_pair_buck_coul.html,
"cg/cmm"_pair_cmm.html,
"cg/cmm/coul/cut"_pair_cmm.html,
"cg/cmm/coul/long"_pair_cmm.html,
"eam/cd"_pair_eam.html,
"lj/coul"_pair_lj_coul.html :tb(c=4,ea=c)
:line
Bond_style potentials :h4
See the "bond_style"_bond_style.html command for an overview of bond
potentials. Click on the style itself for a full description:
"none"_bond_none.html,
"hybrid"_bond_hybrid.html,
"class2"_bond_class2.html,
"fene"_bond_fene.html,
"fene/expand"_bond_fene_expand.html,
"harmonic"_bond_harmonic.html,
"morse"_bond_morse.html,
"nonlinear"_bond_nonlinear.html,
"quartic"_bond_quartic.html,
"table"_bond_table.html :tb(c=4,ea=c,w=100)
:line
Angle_style potentials :h4
See the "angle_style"_angle_style.html command for an overview of
angle potentials. Click on the style itself for a full description:
"none"_angle_none.html,
"hybrid"_angle_hybrid.html,
"charmm"_angle_charmm.html,
"class2"_angle_class2.html,
"cosine"_angle_cosine.html,
"cosine/delta"_angle_cosine_delta.html,
"cosine/squared"_angle_cosine_squared.html,
"harmonic"_angle_harmonic.html,
"table"_angle_table.html :tb(c=4,ea=c,w=100)
These are angle styles contributed by users, which can be used if
"LAMMPS is built with the appropriate package"_Section_start.html#2_3.
"cg/cmm"_angle_cmm.html :tb(c=4,ea=c)
:line
Dihedral_style potentials :h4
See the "dihedral_style"_dihedral_style.html command for an overview
of dihedral potentials. Click on the style itself for a full
description:
"none"_dihedral_none.html,
"hybrid"_dihedral_hybrid.html,
"charmm"_dihedral_charmm.html,
"class2"_dihedral_class2.html,
"harmonic"_dihedral_harmonic.html,
"helix"_dihedral_helix.html,
"multi/harmonic"_dihedral_multi_harmonic.html,
"opls"_dihedral_opls.html :tb(c=4,ea=c,w=100)
:line
Improper_style potentials :h4
See the "improper_style"_improper_style.html command for an overview
of improper potentials. Click on the style itself for a full
description:
"none"_improper_none.html,
"hybrid"_improper_hybrid.html,
"class2"_improper_class2.html,
"cvff"_improper_cvff.html,
"harmonic"_improper_harmonic.html :tb(c=4,ea=c,w=100)
:line
Kspace solvers :h4
See the "kspace_style"_kspace_style.html command for an overview of
Kspace solvers. Click on the style itself for a full description:
"ewald"_kspace_style.html,
"pppm"_kspace_style.html,
"pppm/tip4p"_kspace_style.html :tb(c=4,ea=c,w=100)
These are Kspace solvers contributed by users, which can be used if
"LAMMPS is built with the appropriate package"_Section_start.html#2_3.
"ewald/n"_kspace_style.html :tb(c=4,ea=c,w=100)
diff --git a/doc/Section_howto.html b/doc/Section_howto.html
index 7aff4366c..ef1d0367e 100644
--- a/doc/Section_howto.html
+++ b/doc/Section_howto.html
@@ -1,1465 +1,1473 @@
<HTML>
<CENTER><A HREF = "Section_commands.html">Previous Section</A> - <A HREF = "http://lammps.sandia.gov">LAMMPS WWW Site</A> - <A HREF = "Manual.html">LAMMPS Documentation</A> - <A HREF = "Section_commands.html#comm">LAMMPS Commands</A> - <A HREF = "Section_example.html">Next Section</A>
</CENTER>
<HR>
<H3>4. How-to discussions
</H3>
<P>The following sections describe what commands can be used to perform
certain kinds of LAMMPS simulations.
</P>
4.1 <A HREF = "#4_1">Restarting a simulation</A><BR>
4.2 <A HREF = "#4_2">2d simulations</A><BR>
4.3 <A HREF = "#4_3">CHARMM and AMBER force fields</A><BR>
4.4 <A HREF = "#4_4">Running multiple simulations from one input script</A><BR>
4.5 <A HREF = "#4_5">Parallel tempering</A><BR>
4.6 <A HREF = "#4_6">Granular models</A><BR>
4.7 <A HREF = "#4_7">TIP3P water model</A><BR>
4.8 <A HREF = "#4_8">TIP4P water model</A><BR>
4.9 <A HREF = "#4_9">SPC water model</A><BR>
4.10 <A HREF = "#4_10">Coupling LAMMPS to other codes</A><BR>
4.11 <A HREF = "#4_11">Visualizing LAMMPS snapshots</A><BR>
4.12 <A HREF = "#4_12">Non-orthogonal simulation boxes</A><BR>
4.13 <A HREF = "#4_13">NEMD simulations</A><BR>
4.14 <A HREF = "#4_14">Extended spherical and aspherical particles</A><BR>
4.15 <A HREF = "#4_15">Output from LAMMPS (thermo, dumps, computes, fixes, variables)</A><BR>
4.16 <A HREF = "#4_16">Thermostatting, barostatting and computing temperature</A><BR>
4.17 <A HREF = "#4_17">Walls</A> <BR>
<P>The example input scripts included in the LAMMPS distribution and
highlighted in <A HREF = "Section_example.html">this section</A> also show how to
setup and run various kinds of problems.
</P>
<HR>
<A NAME = "4_1"></A><H4>4.1 Restarting a simulation
</H4>
<P>There are 3 ways to continue a long LAMMPS simulation. Multiple
<A HREF = "run.html">run</A> commands can be used in the same input script. Each
run will continue from where the previous run left off. Or binary
restart files can be saved to disk using the <A HREF = "restart.html">restart</A>
command. At a later time, these binary files can be read via a
<A HREF = "read_restart.html">read_restart</A> command in a new script. Or they can
be converted to text data files and read by a
<A HREF = "read_data.html">read_data</A> command in a new script. <A HREF = "Section_tools.html">This
section</A> discusses the <I>restart2data</I> tool that is
used to perform the conversion.
</P>
<P>Here we give examples of 2 scripts that read either a binary restart
file or a converted data file and then issue a new run command to
continue where the previous run left off. They illustrate what
settings must be made in the new script. Details are discussed in the
documentation for the <A HREF = "read_restart.html">read_restart</A> and
<A HREF = "read_data.html">read_data</A> commands.
</P>
<P>Look at the <I>in.chain</I> input script provided in the <I>bench</I> directory
of the LAMMPS distribution to see the original script that these 2
scripts are based on. If that script had the line
</P>
<PRE>restart 50 tmp.restart
</PRE>
<P>added to it, it would produce 2 binary restart files (tmp.restart.50
and tmp.restart.100) as it ran.
</P>
<P>This script could be used to read the 1st restart file and re-run the
last 50 timesteps:
</P>
<PRE>read_restart tmp.restart.50
</PRE>
<PRE>neighbor 0.4 bin
neigh_modify every 1 delay 1
</PRE>
<PRE>fix 1 all nve
fix 2 all langevin 1.0 1.0 10.0 904297
</PRE>
<PRE>timestep 0.012
</PRE>
<PRE>run 50
</PRE>
<P>Note that the following commands do not need to be repeated because
their settings are included in the restart file: <I>units, atom_style,
special_bonds, pair_style, bond_style</I>. However these commands do
need to be used, since their settings are not in the restart file:
<I>neighbor, fix, timestep</I>.
</P>
<P>If you actually use this script to perform a restarted run, you will
notice that the thermodynamic data match at step 50 (if you also put a
"thermo 50" command in the original script), but do not match at step
100. This is because the <A HREF = "fix_langevin.html">fix langevin</A> command
uses random numbers in a way that does not allow for perfect restarts.
</P>
<P>As an alternate approach, the restart file could be converted to a data
file using this tool:
</P>
<PRE>restart2data tmp.restart.50 tmp.restart.data
</PRE>
<P>Then, this script could be used to re-run the last 50 steps:
</P>
<PRE>units lj
atom_style bond
pair_style lj/cut 1.12
pair_modify shift yes
bond_style fene
special_bonds 0.0 1.0 1.0
</PRE>
<PRE>read_data tmp.restart.data
</PRE>
<PRE>neighbor 0.4 bin
neigh_modify every 1 delay 1
</PRE>
<PRE>fix 1 all nve
fix 2 all langevin 1.0 1.0 10.0 904297
</PRE>
<PRE>timestep 0.012
</PRE>
<PRE>reset_timestep 50
run 50
</PRE>
<P>Note that nearly all the settings specified in the original <I>in.chain</I>
script must be repeated, except the <I>pair_coeff</I> and <I>bond_coeff</I>
commands since the new data file lists the force field coefficients.
Also, the <A HREF = "reset_timestep.html">reset_timestep</A> command is used to tell
LAMMPS the current timestep. This value is stored in restart files,
but not in data files.
</P>
<HR>
<A NAME = "4_2"></A><H4>4.2 2d simulations
</H4>
<P>Use the <A HREF = "dimension.html">dimension</A> command to specify a 2d simulation.
</P>
<P>Make the simulation box periodic in z via the <A HREF = "boundary.html">boundary</A>
command. This is the default.
</P>
<P>If using the <A HREF = "create_box.html">create box</A> command to define a
simulation box, set the z dimensions narrow, but finite, so that the
create_atoms command will tile the 3d simulation box with a single z
plane of atoms - e.g.
</P>
<PRE><A HREF = "create_box.html">create box</A> 1 -10 10 -10 10 -0.25 0.25
</PRE>
<P>If using the <A HREF = "read_data.html">read data</A> command to read in a file of
atom coordinates, set the "zlo zhi" values to be finite but narrow,
similar to the create_box command settings just described. For each
atom in the file, assign a z coordinate so it falls inside the
z-boundaries of the box - e.g. 0.0.
</P>
<P>Use the <A HREF = "fix_enforce2d.html">fix enforce2d</A> command as the last
defined fix to insure that the z-components of velocities and forces
are zeroed out every timestep. The reason to make it the last fix is
so that any forces induced by other fixes will be zeroed out.
</P>
<P>Many of the example input scripts included in the LAMMPS distribution
are for 2d models.
</P>
<P>IMPORTANT NOTE: Some models in LAMMPS treat particles as extended
spheres, as opposed to point particles. In 2d, the particles will
still be spheres, not disks, meaning their moment of inertia will be
the same as in 3d.
</P>
<HR>
<A NAME = "4_3"></A><H4>4.3 CHARMM and AMBER force fields
</H4>
<P>There are many different ways to compute forces in the <A HREF = "http://www.scripps.edu/brooks">CHARMM</A>
and <A HREF = "http://amber.scripps.edu">AMBER</A> molecular dynamics codes, only some of which are
available as options in LAMMPS. A force field has 2 parts: the
formulas that define it and the coefficients used for a particular
system. Here we only discuss formulas implemented in LAMMPS. Setting
coefficients is done in the input data file via the
<A HREF = "read_data.html">read_data</A> command or in the input script with
commands like <A HREF = "pair_coeff.html">pair_coeff</A> or
<A HREF = "bond_coeff.html">bond_coeff</A>. See <A HREF = "Section_tools.html">this section</A> for
additional tools that can use CHARMM or AMBER to assign force field
coefficients and convert their output into LAMMPS input.
</P>
<P>See <A HREF = "#MacKerell">(MacKerell)</A> for a description of the CHARMM force
field. See <A HREF = "#Cornell">(Cornell)</A> for a description of the AMBER force
field.
</P>
<P>These style choices compute force field formulas that are consistent
with common options in CHARMM or AMBER. See each command's
documentation for the formula it computes.
</P>
<UL><LI><A HREF = "bond_style.html">bond_style</A> harmonic
<LI><A HREF = "angle_style.html">angle_style</A> charmm
<LI><A HREF = "dihedral_style.html">dihedral_style</A> charmm
<LI><A HREF = "pair_style.html">pair_style</A> lj/charmm/coul/charmm
<LI><A HREF = "pair_style.html">pair_style</A> lj/charmm/coul/charmm/implicit
<LI><A HREF = "pair_style.html">pair_style</A> lj/charmm/coul/long
</UL>
<UL><LI><A HREF = "special_bonds.html">special_bonds</A> charmm
<LI><A HREF = "special_bonds.html">special_bonds</A> amber
</UL>
<HR>
<A NAME = "4_4"></A><H4>4.4 Running multiple simulations from one input script
</H4>
<P>This can be done in several ways. See the documentation for
individual commands for more details on how these examples work.
</P>
<P>If "multiple simulations" means continue a previous simulation for
more timesteps, then you simply use the <A HREF = "run.html">run</A> command
multiple times. For example, this script
</P>
<PRE>units lj
atom_style atomic
read_data data.lj
run 10000
run 10000
run 10000
run 10000
run 10000
</PRE>
<P>would run 5 successive simulations of the same system for a total of
50,000 timesteps.
</P>
<P>If you wish to run totally different simulations, one after the other,
the <A HREF = "clear.html">clear</A> command can be used in between them to
re-initialize LAMMPS. For example, this script
</P>
<PRE>units lj
atom_style atomic
read_data data.lj
run 10000
clear
units lj
atom_style atomic
read_data data.lj.new
run 10000
</PRE>
<P>would run 2 independent simulations, one after the other.
</P>
<P>For large numbers of independent simulations, you can use
<A HREF = "variable.html">variables</A> and the <A HREF = "next.html">next</A> and
<A HREF = "jump.html">jump</A> commands to loop over the same input script
multiple times with different settings. For example, this
script, named in.polymer
</P>
<PRE>variable d index run1 run2 run3 run4 run5 run6 run7 run8
shell cd $d
read_data data.polymer
run 10000
shell cd ..
clear
next d
jump in.polymer
</PRE>
<P>would run 8 simulations in different directories, using a data.polymer
file in each directory. The same concept could be used to run the
same system at 8 different temperatures, using a temperature variable
and storing the output in different log and dump files, for example
</P>
<PRE>variable a loop 8
variable t index 0.8 0.85 0.9 0.95 1.0 1.05 1.1 1.15
log log.$a
read data.polymer
velocity all create $t 352839
fix 1 all nvt $t $t 100.0
dump 1 all atom 1000 dump.$a
run 100000
next t
next a
jump in.polymer
</PRE>
<P>All of the above examples work whether you are running on 1 or
multiple processors, but assumed you are running LAMMPS on a single
partition of processors. LAMMPS can be run on multiple partitions via
the "-partition" command-line switch as described in <A HREF = "Section_start.html#2_6">this
section</A> of the manual.
</P>
<P>In the last 2 examples, if LAMMPS were run on 3 partitions, the same
scripts could be used if the "index" and "loop" variables were
replaced with <I>universe</I>-style variables, as described in the
<A HREF = "variable.html">variable</A> command. Also, the "next t" and "next a"
commands would need to be replaced with a single "next a t" command.
With these modifications, the 8 simulations of each script would run
on the 3 partitions one after the other until all were finished.
Initially, 3 simulations would be started simultaneously, one on each
partition. When one finished, that partition would then start
the 4th simulation, and so forth, until all 8 were completed.
</P>
<HR>
<A NAME = "4_5"></A><H4>4.5 Parallel tempering
</H4>
<P>The <A HREF = "temper.html">temper</A> command can be used to perform a parallel
tempering or replica-exchange simulation where multiple copies of a
simulation are run at different temperatures on different sets of
processors, and Monte Carlo temperature swaps are performed between
pairs of copies.
</P>
<P>Use the -procs and -in <A HREF = "Section_start.html#2_6">command-line switches</A>
to launch LAMMPS on multiple partitions.
</P>
<P>In your input script, define a set of temperatures, one for each
processor partition, using the <A HREF = "variable.html">variable</A> command:
</P>
<PRE>variable t world 300.0 310.0 320.0 330.0
</PRE>
<P>Define a fix of style <A HREF = "fix_nh.html">nvt</A> or <A HREF = "fix_langevin.html">langevin</A>
to control the temperature of each simulation:
</P>
<PRE>fix myfix all nvt $t $t 100.0
</PRE>
<P>Use the <A HREF = "temper.html">temper</A> command in place of a <A HREF = "run.html">run</A>
command to perform a simulation where tempering exchanges will take
place:
</P>
<PRE>temper 100000 100 $t myfix 3847 58382
</PRE>
<HR>
<A NAME = "4_6"></A><H4>4.6 Granular models
</H4>
<P>Granular system are composed of spherical particles with a diameter,
as opposed to point particles. This means they have an angular
velocity and torque can be imparted to them to cause them to rotate.
</P>
<P>To run a simulation of a granular model, you will want to use
the following commands:
</P>
<UL><LI><A HREF = "atom_style.html">atom_style</A> granular
<LI><A HREF = "fix_nve_sphere.html">fix nve/sphere</A>
<LI><A HREF = "fix_gravity.html">fix gravity</A>
</UL>
<P>This compute
</P>
<UL><LI><A HREF = "compute_erotate_sphere.html">compute erotate/sphere</A>
</UL>
<P>calculates rotational kinetic energy which can be <A HREF = "Section_howto.html#4_15">output with
thermodynamic info</A>.
</P>
<P>Use one of these 3 pair potentials, which compute forces and torques
between interacting pairs of particles:
</P>
<UL><LI><A HREF = "pair_style.html">pair_style</A> gran/history
<LI><A HREF = "pair_style.html">pair_style</A> gran/no_history
<LI><A HREF = "pair_style.html">pair_style</A> gran/hertzian
</UL>
<P>These commands implement fix options specific to granular systems:
</P>
<UL><LI><A HREF = "fix_freeze.html">fix freeze</A>
<LI><A HREF = "fix_pour.html">fix pour</A>
<LI><A HREF = "fix_viscous.html">fix viscous</A>
<LI><A HREF = "fix_wall_gran.html">fix wall/gran</A>
</UL>
<P>The fix style <I>freeze</I> zeroes both the force and torque of frozen
atoms, and should be used for granular system instead of the fix style
<I>setforce</I>.
</P>
<P>For computational efficiency, you can eliminate needless pairwise
computations between frozen atoms by using this command:
</P>
<UL><LI><A HREF = "neigh_modify.html">neigh_modify</A> exclude
</UL>
<HR>
<A NAME = "4_7"></A><H4>4.7 TIP3P water model
</H4>
<P>The TIP3P water model as implemented in CHARMM
<A HREF = "#MacKerell">(MacKerell)</A> specifies a 3-site rigid water molecule with
charges and Lennard-Jones parameters assigned to each of the 3 atoms.
In LAMMPS the <A HREF = "fix_shake.html">fix shake</A> command can be used to hold
the two O-H bonds and the H-O-H angle rigid. A bond style of
<I>harmonic</I> and an angle style of <I>harmonic</I> or <I>charmm</I> should also be
used.
</P>
<P>These are the additional parameters (in real units) to set for O and H
atoms and the water molecule to run a rigid TIP3P-CHARMM model with a
cutoff. The K values can be used if a flexible TIP3P model (without
fix shake) is desired. If the LJ epsilon and sigma for HH and OH are
set to 0.0, it corresponds to the original 1983 TIP3P model
<A HREF = "#Jorgensen">(Jorgensen)</A>.
</P>
<P>O mass = 15.9994<BR>
H mass = 1.008 <BR>
</P>
<P>O charge = -0.834<BR>
H charge = 0.417 <BR>
</P>
<P>LJ epsilon of OO = 0.1521<BR>
LJ sigma of OO = 3.1507<BR>
LJ epsilon of HH = 0.0460<BR>
LJ sigma of HH = 0.4000<BR>
LJ epsilon of OH = 0.0836<BR>
LJ sigma of OH = 1.7753 <BR>
</P>
<P>K of OH bond = 450<BR>
r0 of OH bond = 0.9572 <BR>
</P>
<P>K of HOH angle = 55<BR>
theta of HOH angle = 104.52 <BR>
</P>
<P>These are the parameters to use for TIP3P with a long-range Coulombic
solver (Ewald or PPPM in LAMMPS), see <A HREF = "#Price">(Price)</A> for details:
</P>
<P>O mass = 15.9994<BR>
H mass = 1.008 <BR>
</P>
<P>O charge = -0.830<BR>
H charge = 0.415 <BR>
</P>
<P>LJ epsilon of OO = 0.102<BR>
LJ sigma of OO = 3.188<BR>
LJ epsilon, sigma of OH, HH = 0.0 <BR>
</P>
<P>K of OH bond = 450<BR>
r0 of OH bond = 0.9572 <BR>
</P>
<P>K of HOH angle = 55<BR>
theta of HOH angle = 104.52 <BR>
</P>
<HR>
<A NAME = "4_8"></A><H4>4.8 TIP4P water model
</H4>
<P>The four-point TIP4P rigid water model extends the traditional
three-point TIP3P model by adding an additional site, usually
massless, where the charge associated with the oxygen atom is placed.
This site M is located at a fixed distance away from the oxygen along
the bisector of the HOH bond angle. A bond style of <I>harmonic</I> and an
angle style of <I>harmonic</I> or <I>charmm</I> should also be used.
</P>
<P>Currently, only a four-point model for long-range Coulombics is
implemented via the LAMMPS <A HREF = "pair_lj.html">pair style
lj/cut/coul/long/tip4p</A>. A cutoff version may be added
the future. For both models, the bond lengths and bond angles should
be held fixed using the <A HREF = "fix_shake.html">fix shake</A> command.
</P>
<P>These are the additional parameters (in real units) to set for O and H
atoms and the water molecule to run a rigid TIP4P model with a cutoff
<A HREF = "#Jorgensen">(Jorgensen)</A>. Note that the OM distance is specified in
the <A HREF = "pair_style.html">pair_style</A> command, not as part of the pair
coefficients.
</P>
<P>O mass = 15.9994<BR>
H mass = 1.008 <BR>
</P>
<P>O charge = -1.040<BR>
H charge = 0.520 <BR>
</P>
<P>r0 of OH bond = 0.9572<BR>
theta of HOH angle = 104.52 <BR>
</P>
<P>OM distance = 0.15 <BR>
</P>
<P>LJ epsilon of O-O = 0.1550<BR>
LJ sigma of O-O = 3.1536<BR>
LJ epsilon, sigma of OH, HH = 0.0 <BR>
</P>
<P>These are the parameters to use for TIP4P with a long-range Coulombic
solver (Ewald or PPPM in LAMMPS):
</P>
<P>O mass = 15.9994<BR>
H mass = 1.008 <BR>
</P>
<P>O charge = -1.0484<BR>
H charge = 0.5242 <BR>
</P>
<P>r0 of OH bond = 0.9572<BR>
theta of HOH angle = 104.52 <BR>
</P>
<P>OM distance = 0.1250 <BR>
</P>
<P>LJ epsilon of O-O = 0.16275<BR>
LJ sigma of O-O = 3.16435<BR>
LJ epsilon, sigma of OH, HH = 0.0 <BR>
</P>
<HR>
<A NAME = "4_9"></A><H4>4.9 SPC water model
</H4>
<P>The SPC water model specifies a 3-site rigid water molecule with
charges and Lennard-Jones parameters assigned to each of the 3 atoms.
In LAMMPS the <A HREF = "fix_shake.html">fix shake</A> command can be used to hold
the two O-H bonds and the H-O-H angle rigid. A bond style of
<I>harmonic</I> and an angle style of <I>harmonic</I> or <I>charmm</I> should also be
used.
</P>
<P>These are the additional parameters (in real units) to set for O and H
atoms and the water molecule to run a rigid SPC model with long-range
Coulombics (Ewald or PPPM in LAMMPS).
</P>
<P>O mass = 15.9994<BR>
H mass = 1.008 <BR>
</P>
<P>O charge = -0.820<BR>
H charge = 0.410 <BR>
</P>
<P>LJ epsilon of OO = 0.1553<BR>
LJ sigma of OO = 3.166<BR>
LJ epsilon, sigma of OH, HH = 0.0 <BR>
</P>
<P>r0 of OH bond = 1.0<BR>
theta of HOH angle = 109.47 <BR>
</P>
<P>To use SPC with a long-range Coulombic solver (Ewald or PPPM in
LAMMPS), the only parameters that change are the partial charge
assignments:
</P>
<P>O charge = -0.8476<BR>
H charge = 0.4238 <BR>
</P>
<HR>
<A NAME = "4_10"></A><H4>4.10 Coupling LAMMPS to other codes
</H4>
<P>LAMMPS is designed to allow it to be coupled to other codes. For
example, a quantum mechanics code might compute forces on a subset of
atoms and pass those forces to LAMMPS. Or a continuum finite element
(FE) simulation might use atom positions as boundary conditions on FE
nodal points, compute a FE solution, and return interpolated forces on
MD atoms.
</P>
<P>LAMMPS can be coupled to other codes in at least 3 ways. Each has
advantages and disadvantages, which you'll have to think about in the
context of your application.
</P>
<P>(1) Define a new <A HREF = "fix.html">fix</A> command that calls the other code. In
this scenario, LAMMPS is the driver code. During its timestepping,
the fix is invoked, and can make library calls to the other code,
which has been linked to LAMMPS as a library. This is the way the
<A HREF = "http://www.rpi.edu/~anderk5/lab">POEMS</A> package that performs constrained rigid-body motion on
groups of atoms is hooked to LAMMPS. See the
<A HREF = "fix_poems.html">fix_poems</A> command for more details. See <A HREF = "Section_modify.html">this
section</A> of the documentation for info on how to add
a new fix to LAMMPS.
</P>
<P>(2) Define a new LAMMPS command that calls the other code. This is
conceptually similar to method (1), but in this case LAMMPS and the
other code are on a more equal footing. Note that now the other code
is not called during the timestepping of a LAMMPS run, but between
runs. The LAMMPS input script can be used to alternate LAMMPS runs
with calls to the other code, invoked via the new command. The
<A HREF = "run.html">run</A> command facilitates this with its <I>every</I> option, which
makes it easy to run a few steps, invoke the command, run a few steps,
invoke the command, etc.
</P>
<P>In this scenario, the other code can be called as a library, as in
(1), or it could be a stand-alone code, invoked by a system() call
made by the command (assuming your parallel machine allows one or more
processors to start up another program). In the latter case the
stand-alone code could communicate with LAMMPS thru files that the
command writes and reads.
</P>
<P>See <A HREF = "Section_modify.html">this section</A> of the documentation for how to
add a new command to LAMMPS.
</P>
<P>(3) Use LAMMPS as a library called by another code. In this case the
other code is the driver and calls LAMMPS as needed. Or a wrapper
code could link and call both LAMMPS and another code as libraries.
Again, the <A HREF = "run.html">run</A> command has options that allow it to be
invoked with minimal overhead (no setup or clean-up) if you wish to do
multiple short runs, driven by another program.
</P>
<P><A HREF = "Section_start.html#2_4">This section</A> of the documentation describes
how to build LAMMPS as a library. Once this is done, you can
interface with LAMMPS either via C++, C, or Fortran (or any other
language that supports a vanilla C-like interface, e.g. a scripting
language). For example, from C++ you could create one (or more)
"instances" of LAMMPS, pass it an input script to process, or execute
individual commands, all by invoking the correct class methods in
LAMMPS. From C or Fortran you can make function calls to do the same
things. Library.cpp and library.h contain such a C interface with the
functions:
</P>
<PRE>void lammps_open(int, char **, MPI_Comm, void **);
void lammps_close(void *);
void lammps_file(void *, char *);
char *lammps_command(void *, char *);
</PRE>
<P>The functions contain C++ code you could write in a C++ application
that was invoking LAMMPS directly. Note that LAMMPS classes are
defined within a LAMMPS namespace (LAMMPS_NS) if you use them
from another C++ application.
</P>
<P>Two of the routines in library.cpp are of particular note. The
lammps_open() function initiates LAMMPS and takes an MPI communicator
as an argument. It returns a pointer to a LAMMPS "object". As with
C++, the lammps_open() function can be called multiple times, to
create multiple instances of LAMMPS.
</P>
<P>LAMMPS will run on the set of processors in the communicator. This
means the calling code can run LAMMPS on all or a subset of
processors. For example, a wrapper script might decide to alternate
between LAMMPS and another code, allowing them both to run on all the
processors. Or it might allocate half the processors to LAMMPS and
half to the other code and run both codes simultaneously before
syncing them up periodically.
</P>
<P>Library.cpp contains a lammps_command() function to which the caller
passes a single LAMMPS command (a string). Thus the calling code can
read or generate a series of LAMMPS commands (e.g. an input script)
one line at a time and pass it thru the library interface to setup a
problem and then run it.
</P>
<P>A few other sample functions are included in library.cpp, but the key
idea is that you can write any functions you wish to define an
interface for how your code talks to LAMMPS and add them to
library.cpp and library.h. The routines you add can access any LAMMPS
data. The examples/couple directory has example C++ and C codes which
show how a stand-alone code can link LAMMPS as a library, run LAMMPS
on a subset of processors, grab data from LAMMPS, change it, and put
it back into LAMMPS.
</P>
<HR>
<A NAME = "4_11"></A><H4>4.11 Visualizing LAMMPS snapshots
</H4>
<P>LAMMPS itself does not do visualization, but snapshots from LAMMPS
simulations can be visualized (and analyzed) in a variety of ways.
</P>
<P>LAMMPS snapshots are created by the <A HREF = "dump.html">dump</A> command which can
create files in several formats. The native LAMMPS dump format is a
text file (see "dump atom" or "dump custom") which can be visualized
by the <A HREF = "Section_tools.html#xmovie">xmovie</A> program, included with the
LAMMPS package. This produces simple, fast 2d projections of 3d
systems, and can be useful for rapid debugging of simulation geometry
and atom trajectories.
</P>
<P>Several programs included with LAMMPS as auxiliary tools can convert
native LAMMPS dump files to other formats. See the
<A HREF = "Section_tools.html">Section_tools</A> doc page for details. The first is
the <A HREF = "Section_tools.html#charmm">ch2lmp tool</A>, which contains a
lammps2pdb Perl script which converts LAMMPS dump files into PDB
files. The second is the <A HREF = "Section_tools.html#arc">lmp2arc tool</A> which
converts LAMMPS dump files into Accelrys' Insight MD program files.
The third is the <A HREF = "Section_tools.html#cfg">lmp2cfg tool</A> which converts
LAMMPS dump files into CFG files which can be read into the
<A HREF = "http://164.107.79.177/Archive/Graphics/A">AtomEye</A> visualizer.
</P>
<P>A Python-based toolkit distributed by our group can read native LAMMPS
dump files, including custom dump files with additional columns of
user-specified atom information, and convert them to various formats
or pipe them into visualization software directly. See the <A HREF = "http://www.cs.sandia.gov/~sjplimp/pizza.html">Pizza.py
WWW site</A> for details. Specifically, Pizza.py can convert
LAMMPS dump files into PDB, XYZ, <A HREF = "http://www.ensight.com">Ensight</A>, and VTK formats.
Pizza.py can pipe LAMMPS dump files directly into the Raster3d and
RasMol visualization programs. Pizza.py has tools that do interactive
3d OpenGL visualization and one that creates SVG images of dump file
snapshots.
</P>
<P>LAMMPS can create XYZ files directly (via "dump xyz") which is a
simple text-based file format used by many visualization programs
including <A HREF = "http://www.ks.uiuc.edu/Research/vmd">VMD</A>.
</P>
<P>LAMMPS can create DCD files directly (via "dump dcd") which can be
read by <A HREF = "http://www.ks.uiuc.edu/Research/vmd">VMD</A> in conjunction with a CHARMM PSF file. Using this
form of output avoids the need to convert LAMMPS snapshots to PDB
files. See the <A HREF = "dump.html">dump</A> command for more information on DCD
files.
</P>
<P>LAMMPS can create XTC files directly (via "dump xtc") which is GROMACS
file format which can also be read by <A HREF = "http://www.ks.uiuc.edu/Research/vmd">VMD</A> for visualization.
See the <A HREF = "dump.html">dump</A> command for more information on XTC files.
</P>
<HR>
<A NAME = "4_12"></A><H4>4.12 Non-orthogonal simulation boxes
</H4>
<P>By default, LAMMPS uses an orthogonal simulation box to encompass the
particles. The <A HREF = "boundary.html">boundary</A> command sets the boundary
conditions of the box (periodic, non-periodic, etc). If the box size
is xprd by yprd by zprd then the 3 mutually orthogonal edge vectors of
an orthogonal simulation box are a = (xprd,0,0), b = (0,yprd,0), and c
= (0,0,zprd).
</P>
<P>LAMMPS also allows non-orthogonal simulation boxes (triclinic
symmetry) to be defined with 3 additional "tilt" parameters which
change the edge vectors of the simulation box to be a = (xprd,0,0), b
= (xy,yprd,0), and c = (xz,yz,zprd). The xy, xz, and yz parameters
can be positive or negative. The simulation box must be periodic in
both dimensions associated with a tilt factor. For example, if xz !=
0.0, then the x and z dimensions must be periodic.
</P>
<P>To avoid extremely tilted boxes (which would be computationally
inefficient), no tilt factor can skew the box more than half the
distance of the parallel box length, which is the 1st dimension in the
tilt factor (x for xz). For example, if xlo = 2 and xhi = 12, then
the x box length is 10 and the xy tilt factor must be between -5 and
5. Similarly, both xz and yz must be between -(xhi-xlo)/2 and
+(yhi-ylo)/2. Note that this is not a limitation, since if the
maximum tilt factor is 5 (as in this example), then configurations
with tilt = ..., -15, -5, 5, 15, 25, ... are all equivalent.
</P>
<P>You tell LAMMPS to use a non-orthogonal box when the simulation box is
defined. This happens in one of 3 ways. If the
<A HREF = "create_box.html">create_box</A> command is used with a region of style
<I>prism</I>, then a non-orthogonal domain is setup. See the
<A HREF = "region.html">region</A> command for details. If the
<A HREF = "read_data.html">read_data</A> command is used to define the simulation
box, and the header of the data file contains a line with the "xy xz
yz" keyword, then a non-orthogonal domain is setup. See the
<A HREF = "read_data.html">read_data</A> command for details. Finally, if the
<A HREF = "read_restart.html">read_restart</A> command reads a restart file which
was written from a simulation using a triclinic box, then a
non-orthogonal box will be enabled for the restarted simulation.
</P>
<P>Note that you can define a non-orthogonal box with all 3 tilt factors
= 0.0, so that it is initially orthogonal. This is necessary if the
box will become non-orthogonal. Alternatively, you can use the
<A HREF = "change_box.html">change_box</A> command to convert a simulation box from
orthogonal to non-orthogonal and vice versa.
</P>
<P>One use of non-orthogonal boxes is to model solid-state crystals with
triclinic symmetry. The <A HREF = "lattice.html">lattice</A> command can be used
with non-orthogonal basis vectors to define a lattice that will tile a
non-orthogonal simulation box via the <A HREF = "create_atoms.html">create_atoms</A>
command. Note that while the box edge vectors a,b,c cannot be
arbitrary vectors (e.g. a must be aligned with the x axis), it is
possible to rotate any crystal's basis vectors so that they meet these
restrictions.
</P>
<P>A second use of non-orthogonal boxes is to shear a bulk solid to study
the response of the material. The <A HREF = "fix_deform.html">fix deform</A>
command can be used for this purpose. It allows dynamic control of
the xy, xz, and yz tilt factors as a simulation runs.
</P>
<P>Another use of non-orthogonal boxes is to perform non-equilibrium MD
(NEMD) simulations, as discussed in the next section.
</P>
<HR>
<A NAME = "4_13"></A><H4>4.13 NEMD simulations
</H4>
<P>Non-equilibrium molecular dynamics or NEMD simulations are typically
used to measure a fluid's rheological properties such as viscosity.
In LAMMPS, such simulations can be performed by first setting up a
non-orthogonal simulation box (see the preceding Howto section).
</P>
<P>A shear strain can be applied to the simulation box at a desired
strain rate by using the <A HREF = "fix_deform.html">fix deform</A> command. The
<A HREF = "fix_nvt_sllod.html">fix nvt/sllod</A> command can be used to thermostat
the sheared fluid and integrate the SLLOD equations of motion for the
system. Fix nvt/sllod uses <A HREF = "compute_temp_deform.html">compute
temp/deform</A> to compute a thermal temperature
by subtracting out the streaming velocity of the shearing atoms. The
velocity profile or other properties of the fluid can be monitored via
the <A HREF = "fix_ave_spatial.html">fix ave/spatial</A> command.
</P>
<P>As discussed in the previous section on non-orthogonal simulation
boxes, the amount of tilt or skew that can be applied is limited by
LAMMPS for computational efficiency to be 1/2 of the parallel box
length. However, <A HREF = "fix_deform.html">fix deform</A> can continuously strain
a box by an arbitrary amount. As discussed in the <A HREF = "fix_deform.html">fix
deform</A> command, when the tilt value reaches a limit,
the box is re-shaped to the opposite limit which is an equivalent
tiling of periodic space. The strain rate can then continue to change
as before. In a long NEMD simulation these box re-shaping events may
occur many times.
</P>
<P>In a NEMD simulation, the "remap" option of <A HREF = "fix_deform.html">fix
deform</A> should be set to "remap v", since that is what
<A HREF = "fix_nvt_sllod.html">fix nvt/sllod</A> assumes to generate a velocity
profile consistent with the applied shear strain rate.
</P>
<P>An alternative method for calculating viscosities is provided via the
<A HREF = "fix_viscosity.html">fix viscosity</A> command.
</P>
<HR>
<A NAME = "4_14"></A><H4>4.14 Extended spherical and aspherical particles
</H4>
<P>Typical MD models treat atoms or particles as point masses.
Sometimes, however, it is desirable to have a model with finite-size
particles such as spherioids or aspherical ellipsoids. The difference
is that such particles have a moment of inertia, rotational energy,
and angular momentum. Rotation is induced by torque from interactions
with other particles.
</P>
<P>LAMMPS has several options for running simulations with these kinds of
particles. The following aspects are discussed in turn:
</P>
<UL><LI>atom styles
<LI>pair potentials
<LI>time integration
<LI>computes, thermodynamics, and dump output
<LI>rigid bodies composed of extended particles
</UL>
<H5>Atom styles
</H5>
<P>There are 3 <A HREF = "atom_style.html">atom styles</A> that allow for definition of
finite-size particles: granular, dipole, ellipsoid.
</P>
<P>Granular particles are spheriods and each particle can have a unique
diameter and mass (or density). These particles store an angular
velocity (omega) and can be acted upon by torque.
</P>
<P>Dipolar particles are typically spheriods with a point dipole and each
particle type has a diamater and mass, set by the <A HREF = "shape.html">shape</A>
and <A HREF = "mass.html">mass</A> commands. These particles store an angular
velocity (omega) and can be acted upon by torque. They also store an
orientation for the point dipole (mu) which has a length set by the
<A HREF = "dipole.html">dipole</A> command. The <A HREF = "set.html">set</A> command can be used
to initialize the orientation of dipole moments.
</P>
<P>Ellipsoid particles are aspherical. Each particle type has an
ellipsoidal shape and mass, defined by the <A HREF = "shape.html">shape</A> and
<A HREF = "mass.html">mass</A> commands. These particles store an angular momentum
and their orientation (quaternion), and can be acted upon by torque.
They do not store an angular velocity (omega), which can be in a
different direction than angular momentum, rather they compute it as
needed. Ellipsoidal particles can also store a dipole moment if an
<A HREF = "atom_style.html">atom_style hybrid ellipsoid dipole</A> is used. The
<A HREF = "set.html">set</A> command can be used to initialize the orientation of
ellipsoidal particles and has a brief explanation of quaternions.
</P>
<P>Note that if one of these atom styles is used (or multiple styles via
the <A HREF = "atom_style.html">atom_style hybrid</A> command), not all particles in
the system are required to be finite-size or aspherical. For example,
if the 3 shape parameters are set to the same value, the particle will
be a spheroid rather than an ellipsoid. If the 3 shape parameters are
all set to 0.0 or if the diameter is set to 0.0, it will be a point
particle. If the dipole moment is set to zero, the particle will not
have a point dipole associated with it. The pair styles used to
compute pairwise interactions will typically compute the correct
interaction in these simplified (cheaper) cases. <A HREF = "pair_hybrid.html">Pair_style
hybrid</A> can be used to insure the correct
interactions are computed for the appropriate style of interactions.
Likewise, using groups to partition particles (ellipsoid versus
spheroid versus point particles) will allow you to use the appropriate
time integrators and temperature computations for each class of
particles. See the doc pages for various commands for details.
</P>
<P>Also note that for <A HREF = "dimension.html">2d simulations</A>, finite-size
spheroids and ellipsoids are still treated as 3d particles, rather
than as disks or ellipses. This means they have the same moment of
inertia for a 3d extended object. When their temperature is
coomputed, the correct degrees of freedom are used for rotation in a
2d versus 3d system.
</P>
<H5>Pair potentials
</H5>
<P>When a system with extended particles is defined, the particles will
only rotate and experience torque if the force field computes such
interactions. These are the various <A HREF = "pair_style.html">pair styles</A>
that generate torque:
</P>
<UL><LI><A HREF = "pair_gran.html">pair_style gran/history</A>
<LI><A HREF = "pair_gran.html">pair_style gran/hertzian</A>
<LI><A HREF = "pair_gran.html">pair_style gran/no_history</A>
<LI><A HREF = "pair_dipole.html">pair_style dipole/cut</A>
<LI><A HREF = "pair_gayberne.html">pair_style gayberne</A>
<LI><A HREF = "pair_resuared.html">pair_style resquared</A>
<LI><A HREF = "pair_lubricate.html">pair_style lubricate</A>
</UL>
<P>The <A HREF = "pair_gran.html">granular pair styles</A> are used with <A HREF = "atom_style.html">atom_style
granular</A>. The <A HREF = "pair_dipole.html">dipole pair style</A>
is used with <A HREF = "atom_style.html">atom_style dipole</A>. The
<A HREF = "pair_gayberne.html">GayBerne</A> and <A HREF = "pair_resquared.html">REsquared</A>
potentials require particles have a <A HREF = "shape.html">shape</A> and are
designed for <A HREF = "atom_style.html">ellipsoidal particles</A>. The
<A HREF = "pair_lubricate.html">lubrication potential</A> requires that particles
have a <A HREF = "shape.html">shape</A>. It can currently only be used with
extended spherical particles.
</P>
<H5>Time integration
</H5>
<P>There are 3 fixes that perform time integration on extended spherical
particles, meaning the integrators update the rotational orientation
and angular velocity or angular momentum of the particles:
</P>
<UL><LI><A HREF = "fix_nve_sphere.html">fix nve/sphere</A>
<LI><A HREF = "fix_nvt_sphere.html">fix nvt/sphere</A>
<LI><A HREF = "fix_npt_sphere.html">fix npt/sphere</A>
</UL>
<P>Likewise, there are 3 fixes that perform time integration on extended
aspherical particles:
</P>
<UL><LI><A HREF = "fix_nve_asphere.html">fix nve/asphere</A>
<LI><A HREF = "fix_nvt_asphere.html">fix nvt/asphere</A>
<LI><A HREF = "fix_npt_asphere.html">fix npt/asphere</A>
</UL>
<P>The advantage of these fixes is that those which thermostat the
particles include the rotational degrees of freedom in the temperature
calculation and thermostatting. Other thermostats can be used with
fix nve/sphere or fix nve/asphere, such as fix langevin or fix
temp/berendsen, but those thermostats only operate on the
translational kinetic energy of the extended particles.
</P>
<P>Note that for mixtures of point and extended particles, you should
only use these integration fixes on <A HREF = "group.html">groups</A> which contain
extended particles.
</P>
<H5>Computes, thermodynamics, and dump output
</H5>
<P>There are 4 computes that calculate the temperature or rotational energy
of extended spherical or aspherical particles:
</P>
<UL><LI><A HREF = "compute_temp_sphere.html">compute temp/sphere</A>
<LI><A HREF = "compute_temp_asphere.html">compute temp/asphere</A>
<LI><A HREF = "compute_erotate_sphere.html">compute erotate/sphere</A>
<LI><A HREF = "compute_erotate_asphere.html">compute erotate/asphere</A>
</UL>
<P>These include rotational degrees of freedom in their computation. If
you wish the thermodynamic output of temperature or pressure to use
one of these computes (e.g. for a system entirely composed of extended
particles), then the compute can be defined and the
<A HREF = "thermo_modify.html">thermo_modify</A> command used. Note that by
default thermodynamic quantities will be calculated with a temperature
that only includes translational degrees of freedom. See the
<A HREF = "thermo_style.html">thermo_style</A> command for details.
</P>
<P>The <A HREF = "dump.html">dump custom</A> command can output various attributes of
extended particles, including the dipole moment (mu), the angular
velocity (omega), the angular momentum (angmom), the quaternion
(quat), and the torque (tq) on the particle.
</P>
<H5>Rigid bodies composed of extended particles
</H5>
<P>The <A HREF = "fix_rigid.html">fix rigid</A> command treats a collection of
particles as a rigid body, computes its inertia tensor, sums the total
force and torque on the rigid body each timestep due to forces on its
constituent particles, and integrates the motion of the rigid body.
</P>
<P>(NOTE: the feature described in the following paragraph has not yet
been released. It will be soon.)
</P>
<P>If any of the constituent particles of a rigid body are extended
particles (spheroids or ellipsoids), then their contribution to the
inertia tensor of the body is different than if they were point
particles. This means the rotational dynamics of the rigid body will
be different. Thus a model of a dimer is different if the dimer
consists of two point masses versus two extended sphereoids, even if
the two particles have the same mass. Extended particles that
experience torque due to their interaction with other particles will
also impart that torque to a rigid body they are part of.
</P>
<P>See the "fix rigid" command for example of complex rigid-body models
it is possible to define in LAMMPS.
</P>
<P>Note that the <A HREF = "fix_shake.html">fix shake</A> command can also be used to
treat 2, 3, or 4 particles as a rigid body, but it always assumes the
particles are point masses.
</P>
<HR>
<A NAME = "4_15"></A><H4>4.15 Output from LAMMPS (thermo, dumps, computes, fixes, variables)
</H4>
<P>There are four basic kinds of LAMMPS output:
</P>
<UL><LI><A HREF = "thermo_style.html">Thermodynamic output</A>, which is a list
of quantities printed every few timesteps to the screen and logfile.
<LI><A HREF = "dump.html">Dump files</A>, which contain snapshots of atoms and various
per-atom values and are written at a specified frequency.
<LI>Certain fixes can output user-specified quantities to files: <A HREF = "fix_ave_time.html">fix
ave/time</A> for time averaging, <A HREF = "fix_ave_spatial.html">fix
ave/spatial</A> for spatial averaging, and <A HREF = "fix_print.html">fix
print</A> for single-line output of
<A HREF = "variable.html">variables</A>. Fix print can also output to the
screen.
<LI><A HREF = "restart.html">Restart files</A>.
</UL>
<P>A simulation prints one set of thermodynamic output and (optionally)
restart files. It can generate any number of dump files and fix
output files, depending on what <A HREF = "dump.html">dump</A> and <A HREF = "fix.html">fix</A>
commands you specify.
</P>
<P>As discussed below, LAMMPS gives you a variety of ways to determine
what quantities are computed and printed when the thermodynamics,
dump, or fix commands listed above perform output. Throughout this
discussion, note that users can also <A HREF = "Section_modify.html">add their own computes and fixes
to LAMMPS</A> which can then generate values that can
then be output with these commands.
</P>
<P>The following sub-sections discuss different LAMMPS command related
to output and the kind of data they operate on and produce:
</P>
<UL><LI><A HREF = "#global">Global/per-atom/local data</A>
<LI><A HREF = "#scalar">Scalar/vector/array data</A>
<LI><A HREF = "#thermo">Thermodynamic output</A>
<LI><A HREF = "#dump">Dump file output</A>
<LI><A HREF = "#fixoutput">Fixes that write output files</A>
<LI><A HREF = "#computeoutput">Computes that process output quantities</A>
<LI><A HREF = "#fixoutput">Fixes that process output quantities</A>
<LI><A HREF = "#compute">Computes that generate values to output</A>
<LI><A HREF = "#fix">Fixes that generate values to output</A>
<LI><A HREF = "#variable">Variables that generate values to output</A>
<LI><A HREF = "#table">Summary table of output options and data flow between commands</A>
</UL>
<H5><A NAME = "global"></A>Global/per-atom/local data
</H5>
<P>Various output-related commands work with three different styles of
data: global, per-atom, or local. A global datum is one or more
system-wide values, e.g. the temperature of the system. A per-atom
datum is one or more values per atom, e.g. the kinetic energy of each
atom. Local datums are calculated by each processor based on the
atoms it owns, but there may be zero or more per atom, e.g. a list of
bond distances.
</P>
<H5><A NAME = "scalar"></A>Scalar/vector/array data
</H5>
<P>Global, per-atom, and local datums can each come in three kinds: a
single scalar value, a vector of values, or a 2d array of values. The
doc page for a "compute" or "fix" or "variable" that generates data
will specify both the style and kind of data it produces, e.g. a
per-atom vector.
</P>
<P>When a quantity is accessed, as in many of the output commands
discussed below, it can be referenced via the following bracket
notation, where ID in this case is the ID of a compute. The leading
"c_" would be replaced by "f_" for a fix, or "v_" for a variable:
</P>
<DIV ALIGN=center><TABLE BORDER=1 >
<TR><TD >c_ID </TD><TD > entire scalar, vector, or array</TD></TR>
<TR><TD >c_ID[I] </TD><TD > one element of vector, one column of array</TD></TR>
<TR><TD >c_ID[I][J] </TD><TD > one element of array
</TD></TR></TABLE></DIV>
<P>In other words, using one bracket reduces the dimension of the data
once (vector -> scalar, array -> vector). Using two brackets reduces
the dimension twice (array -> scalar). Thus a command that uses
scalar values as input can typically also process elements of a vector
or array.
</P>
<H5><A NAME = "thermo"></A>Thermodynamic output
</H5>
<P>The frequency and format of thermodynamic output is set by the
<A HREF = "thermo.html">thermo</A>, <A HREF = "thermo_style.html">thermo_style</A>, and
<A HREF = "thermo_modify.html">thermo_modify</A> commands. The
<A HREF = "thermo_style.html">thermo_style</A> command also specifies what values
are calculated and written out. Pre-defined keywords can be specified
(e.g. press, etotal, etc). Three additional kinds of keywords can
also be specified (c_ID, f_ID, v_name), where a <A HREF = "compute.html">compute</A>
or <A HREF = "fix.html">fix</A> or <A HREF = "variable.html">variable</A> provides the value to be
output. In each case, the compute, fix, or variable must generate
global values for input to the <A HREF = "dump.html">thermo_style custom</A>
command.
</P>
<H5><A NAME = "dump"></A>Dump file output
</H5>
<P>Dump file output is specified by the <A HREF = "dump.html">dump</A> and
<A HREF = "dump_modify.html">dump_modify</A> commands. There are several
pre-defined formats (dump atom, dump xtc, etc).
</P>
<P>There is also a <A HREF = "dump.html">dump custom</A> format where the user
specifies what values are output with each atom. Pre-defined atom
attributes can be specified (id, x, fx, etc). Three additional kinds
of keywords can also be specified (c_ID, f_ID, v_name), where a
<A HREF = "compute.html">compute</A> or <A HREF = "fix.html">fix</A> or <A HREF = "variable.html">variable</A>
provides the values to be output. In each case, the compute, fix, or
variable must generate per-atom values for input to the <A HREF = "dump.html">dump
custom</A> command.
</P>
<P>There is also a <A HREF = "dump.html">dump local</A> format where the user specifies
what local values to output. A pre-defined index keyword can be
specified to enumuerate the local values. Two additional kinds of
keywords can also be specified (c_ID, f_ID), where a
<A HREF = "compute.html">compute</A> or <A HREF = "fix.html">fix</A> or <A HREF = "variable.html">variable</A>
provides the values to be output. In each case, the compute or fix
must generate local values for input to the <A HREF = "dump.html">dump local</A>
command.
</P>
<H5><A NAME = "fixoutput"></A>Fixes that write output files
</H5>
<P>Three fixes take various quantities as input and can write output
files: <A HREF = "fix_ave_time.html">fix ave/time</A>, <A HREF = "fix_ave_spatial.html">fix
ave/spatial</A>, and <A HREF = "fix_print.html">fix print</A>.
</P>
<P>The <A HREF = "fix_ave_time.html">fix ave/time</A> command enables direct output to
a file and/or time-averaging of global scalars or vectors. The user
specifies one or more quantities as input. These can be global
<A HREF = "compute.html">compute</A> values, global <A HREF = "fix.html">fix</A> values, or
<A HREF = "variable.html">variables</A> of any style except the atom style which
produces per-atom values. Since a variable can refer to keywords used
by the <A HREF = "thermo_style.html">thermo_style custom</A> command (like temp or
press) and individual per-atom values, a wide variety of quantities
can be time averaged and/or output in this way. If the inputs are one
or more scalar values, then the fix generate a global scalar or vector
of output. If the inputs are one or more vector values, then the fix
generates a global vector or array of output. The time-averaged
output of this fix can also be used as input to other output commands.
</P>
<P>The <A HREF = "fix_ave_spatial.html">fix ave/spatial</A> command enables direct
output to a file of spatial-averaged per-atom quantities like those
output in dump files, within 1d layers of the simulation box. The
per-atom quantities can be atom density (mass or number) or atom
attributes such as position, velocity, force. They can also be
per-atom quantities calculated by a <A HREF = "compute.html">compute</A>, by a
<A HREF = "fix.html">fix</A>, or by an atom-style <A HREF = "variable.html">variable</A>. The
spatial-averaged output of this fix can also be used as input to other
output commands.
</P>
<P>The <A HREF = "fix_ave_histo.html">fix ave/histo</A> command enables direct output
to a file of histogrammed quantities, which can be global or per-atom
or local quantities. The histogram output of this fix can also be
used as input to other output commands.
</P>
<P>The <A HREF = "fix_print.html">fix print</A> command can generate a line of output
written to the screen and log file or to a separate file, periodically
during a running simulation. The line can contain one or more
<A HREF = "variable.html">variable</A> values for any style variable except the atom
style). As explained above, variables themselves can contain
references to global values generated by <A HREF = "thermo_style.html">thermodynamic
keywords</A>, <A HREF = "compute.html">computes</A>,
<A HREF = "fix.html">fixes</A>, or other <A HREF = "variable.html">variables</A>, or to per-atom
values for a specific atom. Thus the <A HREF = "fix_print.html">fix print</A>
command is a means to output a wide variety of quantities separate
from normal thermodynamic or dump file output.
</P>
<H5><A NAME = "computeoutput"></A>Computes that process output quantities
</H5>
<P>The <A HREF = "compute_reduce.html">compute reduce</A> and <A HREF = "compute_reduce.html">compute
reduce/region</A> commands take one or more vector
quantities as inputs and "reduce" them (sum, min, max, ave) to scalar
quantities. These are produced as output values which can be used as
input to other output commands.
</P>
<P>The <A HREF = "compute_property_atom.html">compute property/atom</A> command takes a
list of one or more pre-defined atom attributes (id, x, fx, etc) and
stores the values in a per-atom vector or array. These are produced
as output values which can be used as input to other output commands.
The list of atom attributes is the same as for the <A HREF = "dump.html">dump
custom</A> command.
</P>
<P>The <A HREF = "compute_property_local.html">compute property/local</A> command takes
a list of one or more pre-defined local attributes (bond info, angle
info, etc) and stores the values in a local vector or array. These
are produced as output values which can be used as input to other
output commands.
</P>
<H5><A NAME = "fixoutput"></A>Fixes that process output quantities
</H5>
<P>The <A HREF = "fix_ave_atom.html">fix ave/atom</A> command performs time-averaging
of per-atom vectors. The per-atom quantities can be atom attributes
such as position, velocity, force. They can also be per-atom
quantities calculated by a <A HREF = "compute.html">compute</A>, by a
<A HREF = "fix.html">fix</A>, or by an atom-style <A HREF = "variable.html">variable</A>. The
time-averaged per-atom output of this fix can be used as input to
other output commands.
</P>
<H5><A NAME = "compute"></A>Computes that generate values to output
</H5>
<P>Every <A HREF = "compute.html">compute</A> in LAMMPS produces either global or
per-atom or local values. The values can be scalars or vectors or
arrays of data. These values can be output using the other commands
described in this section. The doc page for each compute command
describes what it produces. Computes that produce per-atom or local
values have the word "atom" or "local" in their style name. Computes
without the word "atom" or "local" produce global values.
</P>
<H5><A NAME = "fix"></A>Fixes that generate values to output
</H5>
<P>Some <A HREF = "fix.html">fixes</A> in LAMMPS produces either global or per-atom or
local values which can be accessed by other commands. The values can
be scalars or vectors or arrays of data. These values can be output
using the other commands described in this section. The doc page for
each fix command tells whether it produces any output quantities and
describes them.
</P>
<H5><A NAME = "variable"></A>Variables that generate values to output
</H5>
<P>Every <A HREF = "variable.html">variables</A> defined in an input script generates
either a global scalar value or a per-atom vector (only atom-style
variables) when it is accessed. The formulas used to define equal-
and atom-style variables can contain references to the thermodynamic
keywords and to global and per-atom data generated by computes, fixes,
and other variables. The values generated by variables can be output
using the other commands described in this section.
</P>
<H5><A NAME = "table"></A>Summary table of output options and data flow between commands
</H5>
<P>This table summarizes the various commands that can be used for
generating output from LAMMPS. Each command produces output data of
some kind and/or writes data to a file. Most of the commands can take
data from other commands as input. Thus you can link many of these
commands together in pipeline form, where data produced by one command
is used as input to another command and eventually written to the
screen or to a file. Note that to hook two commands together the
output and input data types must match, e.g. global/per-atom/local
data and scalar/vector/array data.
</P>
<P>Also note that, as described above, when a command takes a scalar as
input, that could be an element of a vector or array. Likewise a
vector input could be a column of an array.
</P>
<DIV ALIGN=center><TABLE BORDER=1 >
<TR><TD >Command</TD><TD > Input</TD><TD > Output</TD><TD ></TD></TR>
<TR><TD ><A HREF = "thermo_style.html">thermo_style custom</A></TD><TD > global scalars</TD><TD > screen, log file</TD><TD ></TD></TR>
<TR><TD ><A HREF = "dump.html">dump custom</A></TD><TD > per-atom vectors</TD><TD > dump file</TD><TD ></TD></TR>
<TR><TD ><A HREF = "dump.html">dump local</A></TD><TD > local vectors</TD><TD > dump file</TD><TD ></TD></TR>
<TR><TD ><A HREF = "fix_print.html">fix print</A></TD><TD > global scalar from variable</TD><TD > screen, file</TD><TD ></TD></TR>
<TR><TD ><A HREF = "print.html">print</A></TD><TD > global scalar from variable</TD><TD > screen</TD><TD ></TD></TR>
<TR><TD ><A HREF = "compute.html">computes</A></TD><TD > N/A</TD><TD > global/per-atom/local scalar/vector/array</TD><TD ></TD></TR>
<TR><TD ><A HREF = "fix.html">fixes</A></TD><TD > N/A</TD><TD > global/per-atom/local scalar/vector/array</TD><TD ></TD></TR>
<TR><TD ><A HREF = "variable.html">variables</A></TD><TD > global scalars, per-atom vectors</TD><TD > global scalar, per-atom vector</TD><TD ></TD></TR>
<TR><TD ><A HREF = "compute_reduce.html">compute reduce</A></TD><TD > global/per-atom/local vectors</TD><TD > global scalar/vector</TD><TD ></TD></TR>
<TR><TD ><A HREF = "compute_property_atom.html">compute property/atom</A></TD><TD > per-atom vectors</TD><TD > per-atom vector/array</TD><TD ></TD></TR>
<TR><TD ><A HREF = "compute_property_local.html">compute property/local</A></TD><TD > local vectors</TD><TD > local vector/array</TD><TD ></TD></TR>
<TR><TD ><A HREF = "fix_ave_atom.html">fix ave/atom</A></TD><TD > per-atom vectors</TD><TD > per-atom vector/array</TD><TD ></TD></TR>
<TR><TD ><A HREF = "fix_ave_time.html">fix ave/time</A></TD><TD > global scalars/vectors</TD><TD > global scalar/vector/array, file</TD><TD ></TD></TR>
<TR><TD ><A HREF = "fix_ave_spatial.html">fix ave/spatial</A></TD><TD > per-atom vectors</TD><TD > global array, file</TD><TD ></TD></TR>
<TR><TD ><A HREF = "fix_ave_histo.html">fix ave/histo</A></TD><TD > global/per-atom/local scalars and vectors</TD><TD > global array, file</TD><TD ></TD></TR>
<TR><TD >
</TD></TR></TABLE></DIV>
<HR>
<A NAME = "4_16"></A><H4>4.16 Thermostatting, barostatting, and computing temperature
</H4>
<P>Thermostatting means controlling the temperature of particles in an MD
simulation. Barostatting means controlling the pressure. Since the
pressure includes a kinetic component due to particle velocities, both
these operations require calculation of the temperature. Typically a
target temperature (T) and/or pressure (P) is specified by the user,
and the thermostat or barostat attempts to equilibrate the system to
the requested T and/or P.
</P>
<P>Temperature is computed as kinetic energy divided by some number of
degrees of freedom (and the Boltzmann constant). Since kinetic energy
is a function of particle velocity, there is often a need to
distinguish between a particle's advection velocity (due to some
aggregate motiion of particles) and its thermal velocity. The sum of
the two is the particle's total velocity, but the latter is often what
is wanted to compute a temperature.
</P>
<P>LAMMPS has several options for computing temperatures, any of which
can be used in thermostatting and barostatting. These <A HREF = "compute.html">compute
commands</A> calculate temperature, and the <A HREF = "compute_pressure.html">compute
pressure</A> command calculates pressure.
</P>
<UL><LI><A HREF = "compute_temp.html">compute temp</A>
<LI><A HREF = "compute_temp_sphere.html">compute temp/sphere</A>
<LI><A HREF = "compute_temp_asphere.html">compute temp/asphere</A>
<LI><A HREF = "compute_temp_com.html">compute temp/com</A>
<LI><A HREF = "compute_temp_deform.html">compute temp/deform</A>
<LI><A HREF = "compute_temp_partial.html">compute temp/partial</A>
<LI><A HREF = "compute_temp_profile.html">compute temp/profile</A>
<LI><A HREF = "compute_temp_ramp.html">compute temp/ramp</A>
<LI><A HREF = "compute_temp_region.html">compute temp/region</A>
</UL>
<P>All but the first 3 calculate velocity biases (i.e. advection
velocities) that are removed when computing the thermal temperature.
<A HREF = "fix_temp_sphere.html">Fix temp/sphere</A> and <A HREF = "fix_temp_asphere.html">fix
temp/asphere</A> compute kinetic energy for
extended particles that includes rotational degrees of freedom. They
both allow, as an extra argument, which is another temperature compute
that subtracts a velocity bias. This allows the translational
velocity of extended spherical or aspherical particles to be adjusted
in prescribed ways.
</P>
-<P>Thermostatting in LAMMPS is performed by <A HREF = "fix.html">fixes</A>. Four
-thermostatting fixes are currently available: Nose-Hoover (nvt),
-Berendsen, Langevin, and direct rescaling (temp/rescale):
+<P>Thermostatting in LAMMPS is performed by <A HREF = "fix.html">fixes</A>, or in one
+case by a pair style. Four thermostatting fixes are currently
+available: Nose-Hoover (nvt), Berendsen, Langevin, and direct
+rescaling (temp/rescale). Dissipative particle dynamics (DPD)
+thermostatting can be invoked via the <I>dpd/tstat</I> pair style:
</P>
<UL><LI><A HREF = "fix_nh.html">fix nvt</A>
<LI><A HREF = "fix_nvt_sphere.html">fix nvt/sphere</A>
<LI><A HREF = "fix_nvt_asphere.html">fix nvt/asphere</A>
<LI><A HREF = "fix_nvt_sllod.html">fix nvt/sllod</A>
<LI><A HREF = "fix_temp_berendsen.html">fix temp/berendsen</A>
<LI><A HREF = "fix_langevin.html">fix langevin</A>
-<LI><A HREF = "fix_temp_rescale.html">fix temp/rescale</A>
+<LI><A HREF = "fix_temp_rescale.html">fix temp/rescale</A>
+<LI><A HREF = "pair_dpd.html">pair_style dpd/tstat</A>
</UL>
<P><A HREF = "fix_nh.html">Fix nvt</A> only thermostats the translational velocity of
particles. <A HREF = "fix_nvt_sllod.html">Fix nvt/sllod</A> also does this, except
that it subtracts out a velocity bias due to a deforming box and
integrates the SLLOD equations of motion. See the <A HREF = "#4_13">NEMD
simulations</A> section of this page for further details. <A HREF = "fix_nvt_sphere.html">Fix
nvt/sphere</A> and <A HREF = "fix_nvt_asphere.html">fix
nvt/asphere</A> thermostat not only translation
velocities but also rotational velocities for spherical and aspherical
particles.
</P>
-<P>Any of these fixes can use temperature computes that remove bias for
-two purposes: (a) computing the current temperature to compare to the
-requested target temperature, and (b) adjusting only the thermal
-temperature component of the particle's velocities. See the doc pages
-for the individual fixes and for the <A HREF = "fix_modify.html">fix_modify</A>
-command for instructions on how to assign a temperature compute to a
-thermostatting fix. For example, you can apply a thermostat to only
-the x and z components of velocity by using it in conjunction with
-<A HREF = "compute_temp_partial.html">compute temp/partial</A>.
+<P>DPD thermostatting alters pairwise interactions in a manner analagous
+to the per-particle thermostatting of <A HREF = "fix_langevin.html">fix
+langevin</A>.
+</P>
+<P>Any of the thermostatting fixes can use temperature computes that
+remove bias for two purposes: (a) computing the current temperature to
+compare to the requested target temperature, and (b) adjusting only
+the thermal temperature component of the particle's velocities. See
+the doc pages for the individual fixes and for the
+<A HREF = "fix_modify.html">fix_modify</A> command for instructions on how to assign
+a temperature compute to a thermostatting fix. For example, you can
+apply a thermostat to only the x and z components of velocity by using
+it in conjunction with <A HREF = "compute_temp_partial.html">compute
+temp/partial</A>.
</P>
<P>IMPORTANT NOTE: Only the nvt fixes perform time integration, meaning
they update the velocities and positions of particles due to forces
and velocities respectively. The other thermostat fixes only adjust
velocities; they do NOT perform time integration updates. Thus they
should be used in conjunction with a constant NVE integration fix such
as these:
</P>
<UL><LI><A HREF = "fix_nve.html">fix nve</A>
<LI><A HREF = "fix_nve_sphere.html">fix nve/sphere</A>
<LI><A HREF = "fix_nve_asphere.html">fix nve/asphere</A>
</UL>
<P>Barostatting in LAMMPS is also performed by <A HREF = "fix.html">fixes</A>. Two
barosttating methods are currently available: Nose-Hoover (npt and
nph) and Berendsen:
</P>
<UL><LI><A HREF = "fix_nh.html">fix npt</A>
<LI><A HREF = "fix_npt_sphere.html">fix npt/sphere</A>
<LI><A HREF = "fix_npt_asphere.html">fix npt/asphere</A>
<LI><A HREF = "fix_nh.html">fix nph</A>
<LI><A HREF = "fix_press_berendsen.html">fix press/berendsen</A>
</UL>
<P>The <A HREF = "fix_nh.html">fix npt</A> commands include a Nose-Hoover thermostat
and barostat. <A HREF = "fix_nh.html">Fix nph</A> is just a Nose/Hoover barostat;
it does no thermostatting. Both <A HREF = "fix_nh.html">fix nph</A> and <A HREF = "fix_press_berendsen.html">fix
press/bernendsen</A> can be used in conjunction
with any of the thermostatting fixes.
</P>
<P>As with the thermostats, <A HREF = "fix_nh.html">fix npt</A> and <A HREF = "fix_nh.html">fix
nph</A> only use translational motion of the particles in
computing T and P and performing thermo/barostatting. <A HREF = "fix_npt_sphere.html">Fix
npt/sphere</A> and <A HREF = "fix_npt_asphere.html">fix
npt/asphere</A> thermo/barostat using not only
translation velocities but also rotational velocities for spherical
and aspherical particles.
</P>
<P>All of the barostatting fixes use the <A HREF = "compute_pressure.html">compute
pressure</A> compute to calculate a current
pressure. By default, this compute is created with a simple <A HREF = "compute_temp.html">compute
temp</A> (see the last argument of the <A HREF = "compute_pressure.html">compute
pressure</A> command), which is used to calculated
the kinetic componenet of the pressure. The barostatting fixes can
also use temperature computes that remove bias for the purpose of
computing the kinetic componenet which contributes to the current
pressure. See the doc pages for the individual fixes and for the
<A HREF = "fix_modify.html">fix_modify</A> command for instructions on how to assign
a temperature or pressure compute to a barostatting fix.
</P>
<P>IMPORTANT NOTE: As with the thermostats, the Nose/Hoover methods (<A HREF = "fix_nh.html">fix
npt</A> and <A HREF = "fix_nh.html">fix nph</A>) perform time
integration. <A HREF = "fix_press_berendsen.html">Fix press/berendsen</A> does NOT,
so it should be used with one of the constant NVE fixes or with one of
the NVT fixes.
</P>
<P>Finally, thermodynamic output, which can be setup via the
<A HREF = "thermo_style.html">thermo_style</A> command, often includes temperature
and pressure values. As explained on the doc page for the
<A HREF = "thermo_style.html">thermo_style</A> command, the default T and P are
setup by the thermo command itself. They are NOT the ones associated
with any thermostatting or barostatting fix you have defined or with
any compute that calculates a temperature or pressure. Thus if you
want to view these values of T and P, you need to specify them
explicitly via a <A HREF = "thermo_style.html">thermo_style custom</A> command. Or
you can use the <A HREF = "thermo_modify.html">thermo_modify</A> command to
re-define what temperature or pressure compute is used for default
thermodynamic output.
</P>
<HR>
<A NAME = "4_17"></A><H4>4.16 Walls
</H4>
<P>Walls in an MD simulation are typically used to bound particle motion,
i.e. to serve as a boundary condition.
</P>
<P>Walls in LAMMPS can be of rough (made of particles) or idealized
surfaces. Ideal walls can be smooth, generating forces only in the
normal direction, or frictional, generating forces also in the
tangential direction.
</P>
<P>Rough walls, built of particles, can be created in various ways. The
particles themselves can be generated like any other particle, via the
<A HREF = "lattice.html">lattice</A> and <A HREF = "create_atoms.html">create_atoms</A> commands,
or read in via the <A HREF = "read_data.html">read_data</A> command.
</P>
<P>Their motion can be constrained by many different commands, so that
they do not move at all, move together as a group at constant velocity
or in response to a net force acting on them, move in a prescribed
fashion (e.g. rotate around a point), etc. Note that if a time
integration fix like <A HREF = "fix_nve.html">fix nve</A> or <A HREF = "fix_nh.html">fix nvt</A>
is not used with the group that contains wall particles, their
positions and velocities will not be updated.
</P>
<UL><LI><A HREF = "fix_aveforce.html">fix aveforce</A> - set force on particles to average value, so they move together
<LI><A HREF = "fix_setforce.html">fix setforce</A> - set force on particles to a value, e.g. 0.0
<LI><A HREF = "fix_freeze.html">fix freeze</A> - freeze particles for use as granular walls
<LI><A HREF = "fix_nve_noforce.html">fix nve/noforce</A> - advect particles by their velocity, but without force
<LI><A HREF = "fix_move.html">fix move</A> - prescribe motion of particles by a linear velocity, oscillation, rotation, variable
</UL>
<P>The <A HREF = "fix_move.html">fix move</A> command offers the most generality, since
the motion of individual particles can be specified with
<A HREF = "variable.html">variable</A> formula which depends on time and/or the
particle position.
</P>
<P>For rough walls, it may be useful to turn off pairwise interactions
between wall particles via the <A HREF = "neigh_modify.html">neigh_modify
exclude</A> command.
</P>
<P>Rough walls can also be created by specifying frozen particles that do
not move and do not interact with mobile particles, and then tethering
other particles to the fixed particles, via a <A HREF = "bond_style.html">bond</A>.
The bonded particles do interact with other mobile particles.
</P>
<P>Idealized walls can be specified via several fix commands. <A HREF = "fix_wall_gran.html">Fix
wall/gran</A> creates frictional walls for use with
granular particles; all the other commands create smooth walls.
</P>
<UL><LI><A HREF = "fix_wall_reflect.html">fix wall/reflect</A> - reflective flat walls
<LI><A HREF = "fix_wall.html">fix wall/lj93</A> - flat walls, with Lennard-Jones 9/3 potential
<LI><A HREF = "fix_wall.html">fix wall/lj126</A> - flat walls, with Lennard-Jones 12/6 potential
<LI><A HREF = "fix_wall.html">fix wall/colloid</A> - flat walls, with <A HREF = "pair_colloid.html">pair_style colloid</A> potential
<LI><A HREF = "fix_wall.html">fix wall/harmonic</A> - flat walls, with repulsive harmonic spring potential
<LI><A HREF = "fix_wall_region.html">fix wall/region</A> - use region surface as wall
<LI><A HREF = "fix_wall_gran.html">fix wall/gran</A> - flat or curved walls with <A HREF = "pair_gran.html">pair_style granular</A> potential
</UL>
<P>The <I>lj93</I>, <I>lj126</I>, <I>colloid</I>, and <I>harmonic</I> styles all allow the
flat walls to move with a constant velocity, or oscillate in time.
The <A HREF = "fix_wall_region.html">fix wall/region</A> command offers the most
generality, since the region surface is treated as a wall, and the
geometry of the region can be a simple primitive volume (e.g. a
sphere, or cube, or plane), or a complex volume made from the union
and intersection of primitive volumes. <A HREF = "region.html">Regions</A> can also
specify a volume "interior" or "exterior" to the specified primitive
shape or <I>union</I> or <I>intersection</I>. <A HREF = "region.html">Regions</A> can also be
"dynamic" meaning they move with constant velocity, oscillate, or
rotate.
</P>
<P>The only frictional idealized walls currently in LAMMPS are flat or
curved surfaces specified by the <A HREF = "fix_wall_gran.html">fix wall/gran</A>
command. At some point we plan to allow regoin surfaces to be used as
frictional walls, as well as triangulated surfaces.
</P>
<HR>
<HR>
<A NAME = "Cornell"></A>
<P><B>(Cornell)</B> Cornell, Cieplak, Bayly, Gould, Merz, Ferguson,
Spellmeyer, Fox, Caldwell, Kollman, JACS 117, 5179-5197 (1995).
</P>
<A NAME = "Horn"></A>
<P><B>(Horn)</B> Horn, Swope, Pitera, Madura, Dick, Hura, and Head-Gordon,
J Chem Phys, 120, 9665 (2004).
</P>
<A NAME = "MacKerell"></A>
<P><B>(MacKerell)</B> MacKerell, Bashford, Bellott, Dunbrack, Evanseck, Field,
Fischer, Gao, Guo, Ha, et al, J Phys Chem, 102, 3586 (1998).
</P>
<A NAME = "Jorgensen"></A>
<P><B>(Jorgensen)</B> Jorgensen, Chandrasekhar, Madura, Impey, Klein, J Chem
Phys, 79, 926 (1983).
</P>
<A NAME = "Price"></A>
<P><B>(Price)</B> Price and Brooks, J Chem Phys, 121, 10096 (2004).
</P>
</HTML>
diff --git a/doc/Section_howto.txt b/doc/Section_howto.txt
index c6000a038..ba5e855d2 100644
--- a/doc/Section_howto.txt
+++ b/doc/Section_howto.txt
@@ -1,1446 +1,1454 @@
"Previous Section"_Section_commands.html - "LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc - "Next Section"_Section_example.html :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Section_commands.html#comm)
:line
4. How-to discussions :h3
The following sections describe what commands can be used to perform
certain kinds of LAMMPS simulations.
4.1 "Restarting a simulation"_#4_1
4.2 "2d simulations"_#4_2
4.3 "CHARMM and AMBER force fields"_#4_3
4.4 "Running multiple simulations from one input script"_#4_4
4.5 "Parallel tempering"_#4_5
4.6 "Granular models"_#4_6
4.7 "TIP3P water model"_#4_7
4.8 "TIP4P water model"_#4_8
4.9 "SPC water model"_#4_9
4.10 "Coupling LAMMPS to other codes"_#4_10
4.11 "Visualizing LAMMPS snapshots"_#4_11
4.12 "Non-orthogonal simulation boxes"_#4_12
4.13 "NEMD simulations"_#4_13
4.14 "Extended spherical and aspherical particles"_#4_14
4.15 "Output from LAMMPS (thermo, dumps, computes, fixes, variables)"_#4_15
4.16 "Thermostatting, barostatting and computing temperature"_#4_16
4.17 "Walls"_#4_17 :all(b)
The example input scripts included in the LAMMPS distribution and
highlighted in "this section"_Section_example.html also show how to
setup and run various kinds of problems.
:line
4.1 Restarting a simulation :link(4_1),h4
There are 3 ways to continue a long LAMMPS simulation. Multiple
"run"_run.html commands can be used in the same input script. Each
run will continue from where the previous run left off. Or binary
restart files can be saved to disk using the "restart"_restart.html
command. At a later time, these binary files can be read via a
"read_restart"_read_restart.html command in a new script. Or they can
be converted to text data files and read by a
"read_data"_read_data.html command in a new script. "This
section"_Section_tools.html discusses the {restart2data} tool that is
used to perform the conversion.
Here we give examples of 2 scripts that read either a binary restart
file or a converted data file and then issue a new run command to
continue where the previous run left off. They illustrate what
settings must be made in the new script. Details are discussed in the
documentation for the "read_restart"_read_restart.html and
"read_data"_read_data.html commands.
Look at the {in.chain} input script provided in the {bench} directory
of the LAMMPS distribution to see the original script that these 2
scripts are based on. If that script had the line
restart 50 tmp.restart :pre
added to it, it would produce 2 binary restart files (tmp.restart.50
and tmp.restart.100) as it ran.
This script could be used to read the 1st restart file and re-run the
last 50 timesteps:
read_restart tmp.restart.50 :pre
neighbor 0.4 bin
neigh_modify every 1 delay 1 :pre
fix 1 all nve
fix 2 all langevin 1.0 1.0 10.0 904297 :pre
timestep 0.012 :pre
run 50 :pre
Note that the following commands do not need to be repeated because
their settings are included in the restart file: {units, atom_style,
special_bonds, pair_style, bond_style}. However these commands do
need to be used, since their settings are not in the restart file:
{neighbor, fix, timestep}.
If you actually use this script to perform a restarted run, you will
notice that the thermodynamic data match at step 50 (if you also put a
"thermo 50" command in the original script), but do not match at step
100. This is because the "fix langevin"_fix_langevin.html command
uses random numbers in a way that does not allow for perfect restarts.
As an alternate approach, the restart file could be converted to a data
file using this tool:
restart2data tmp.restart.50 tmp.restart.data :pre
Then, this script could be used to re-run the last 50 steps:
units lj
atom_style bond
pair_style lj/cut 1.12
pair_modify shift yes
bond_style fene
special_bonds 0.0 1.0 1.0 :pre
read_data tmp.restart.data :pre
neighbor 0.4 bin
neigh_modify every 1 delay 1 :pre
fix 1 all nve
fix 2 all langevin 1.0 1.0 10.0 904297 :pre
timestep 0.012 :pre
reset_timestep 50
run 50 :pre
Note that nearly all the settings specified in the original {in.chain}
script must be repeated, except the {pair_coeff} and {bond_coeff}
commands since the new data file lists the force field coefficients.
Also, the "reset_timestep"_reset_timestep.html command is used to tell
LAMMPS the current timestep. This value is stored in restart files,
but not in data files.
:line
4.2 2d simulations :link(4_2),h4
Use the "dimension"_dimension.html command to specify a 2d simulation.
Make the simulation box periodic in z via the "boundary"_boundary.html
command. This is the default.
If using the "create box"_create_box.html command to define a
simulation box, set the z dimensions narrow, but finite, so that the
create_atoms command will tile the 3d simulation box with a single z
plane of atoms - e.g.
"create box"_create_box.html 1 -10 10 -10 10 -0.25 0.25 :pre
If using the "read data"_read_data.html command to read in a file of
atom coordinates, set the "zlo zhi" values to be finite but narrow,
similar to the create_box command settings just described. For each
atom in the file, assign a z coordinate so it falls inside the
z-boundaries of the box - e.g. 0.0.
Use the "fix enforce2d"_fix_enforce2d.html command as the last
defined fix to insure that the z-components of velocities and forces
are zeroed out every timestep. The reason to make it the last fix is
so that any forces induced by other fixes will be zeroed out.
Many of the example input scripts included in the LAMMPS distribution
are for 2d models.
IMPORTANT NOTE: Some models in LAMMPS treat particles as extended
spheres, as opposed to point particles. In 2d, the particles will
still be spheres, not disks, meaning their moment of inertia will be
the same as in 3d.
:line
4.3 CHARMM and AMBER force fields :link(4_3),h4
There are many different ways to compute forces in the "CHARMM"_charmm
and "AMBER"_amber molecular dynamics codes, only some of which are
available as options in LAMMPS. A force field has 2 parts: the
formulas that define it and the coefficients used for a particular
system. Here we only discuss formulas implemented in LAMMPS. Setting
coefficients is done in the input data file via the
"read_data"_read_data.html command or in the input script with
commands like "pair_coeff"_pair_coeff.html or
"bond_coeff"_bond_coeff.html. See "this section"_Section_tools.html for
additional tools that can use CHARMM or AMBER to assign force field
coefficients and convert their output into LAMMPS input.
See "(MacKerell)"_#MacKerell for a description of the CHARMM force
field. See "(Cornell)"_#Cornell for a description of the AMBER force
field.
:link(charmm,http://www.scripps.edu/brooks)
:link(amber,http://amber.scripps.edu)
These style choices compute force field formulas that are consistent
with common options in CHARMM or AMBER. See each command's
documentation for the formula it computes.
"bond_style"_bond_style.html harmonic
"angle_style"_angle_style.html charmm
"dihedral_style"_dihedral_style.html charmm
"pair_style"_pair_style.html lj/charmm/coul/charmm
"pair_style"_pair_style.html lj/charmm/coul/charmm/implicit
"pair_style"_pair_style.html lj/charmm/coul/long :ul
"special_bonds"_special_bonds.html charmm
"special_bonds"_special_bonds.html amber :ul
:line
4.4 Running multiple simulations from one input script :link(4_4),h4
This can be done in several ways. See the documentation for
individual commands for more details on how these examples work.
If "multiple simulations" means continue a previous simulation for
more timesteps, then you simply use the "run"_run.html command
multiple times. For example, this script
units lj
atom_style atomic
read_data data.lj
run 10000
run 10000
run 10000
run 10000
run 10000 :pre
would run 5 successive simulations of the same system for a total of
50,000 timesteps.
If you wish to run totally different simulations, one after the other,
the "clear"_clear.html command can be used in between them to
re-initialize LAMMPS. For example, this script
units lj
atom_style atomic
read_data data.lj
run 10000
clear
units lj
atom_style atomic
read_data data.lj.new
run 10000 :pre
would run 2 independent simulations, one after the other.
For large numbers of independent simulations, you can use
"variables"_variable.html and the "next"_next.html and
"jump"_jump.html commands to loop over the same input script
multiple times with different settings. For example, this
script, named in.polymer
variable d index run1 run2 run3 run4 run5 run6 run7 run8
shell cd $d
read_data data.polymer
run 10000
shell cd ..
clear
next d
jump in.polymer :pre
would run 8 simulations in different directories, using a data.polymer
file in each directory. The same concept could be used to run the
same system at 8 different temperatures, using a temperature variable
and storing the output in different log and dump files, for example
variable a loop 8
variable t index 0.8 0.85 0.9 0.95 1.0 1.05 1.1 1.15
log log.$a
read data.polymer
velocity all create $t 352839
fix 1 all nvt $t $t 100.0
dump 1 all atom 1000 dump.$a
run 100000
next t
next a
jump in.polymer :pre
All of the above examples work whether you are running on 1 or
multiple processors, but assumed you are running LAMMPS on a single
partition of processors. LAMMPS can be run on multiple partitions via
the "-partition" command-line switch as described in "this
section"_Section_start.html#2_6 of the manual.
In the last 2 examples, if LAMMPS were run on 3 partitions, the same
scripts could be used if the "index" and "loop" variables were
replaced with {universe}-style variables, as described in the
"variable"_variable.html command. Also, the "next t" and "next a"
commands would need to be replaced with a single "next a t" command.
With these modifications, the 8 simulations of each script would run
on the 3 partitions one after the other until all were finished.
Initially, 3 simulations would be started simultaneously, one on each
partition. When one finished, that partition would then start
the 4th simulation, and so forth, until all 8 were completed.
:line
4.5 Parallel tempering :link(4_5),h4
The "temper"_temper.html command can be used to perform a parallel
tempering or replica-exchange simulation where multiple copies of a
simulation are run at different temperatures on different sets of
processors, and Monte Carlo temperature swaps are performed between
pairs of copies.
Use the -procs and -in "command-line switches"_Section_start.html#2_6
to launch LAMMPS on multiple partitions.
In your input script, define a set of temperatures, one for each
processor partition, using the "variable"_variable.html command:
variable t world 300.0 310.0 320.0 330.0 :pre
Define a fix of style "nvt"_fix_nh.html or "langevin"_fix_langevin.html
to control the temperature of each simulation:
fix myfix all nvt $t $t 100.0 :pre
Use the "temper"_temper.html command in place of a "run"_run.html
command to perform a simulation where tempering exchanges will take
place:
temper 100000 100 $t myfix 3847 58382 :pre
:line
4.6 Granular models :link(4_6),h4
Granular system are composed of spherical particles with a diameter,
as opposed to point particles. This means they have an angular
velocity and torque can be imparted to them to cause them to rotate.
To run a simulation of a granular model, you will want to use
the following commands:
"atom_style"_atom_style.html granular
"fix nve/sphere"_fix_nve_sphere.html
"fix gravity"_fix_gravity.html :ul
This compute
"compute erotate/sphere"_compute_erotate_sphere.html :ul
calculates rotational kinetic energy which can be "output with
thermodynamic info"_Section_howto.html#4_15.
Use one of these 3 pair potentials, which compute forces and torques
between interacting pairs of particles:
"pair_style"_pair_style.html gran/history
"pair_style"_pair_style.html gran/no_history
"pair_style"_pair_style.html gran/hertzian :ul
These commands implement fix options specific to granular systems:
"fix freeze"_fix_freeze.html
"fix pour"_fix_pour.html
"fix viscous"_fix_viscous.html
"fix wall/gran"_fix_wall_gran.html :ul
The fix style {freeze} zeroes both the force and torque of frozen
atoms, and should be used for granular system instead of the fix style
{setforce}.
For computational efficiency, you can eliminate needless pairwise
computations between frozen atoms by using this command:
"neigh_modify"_neigh_modify.html exclude :ul
:line
4.7 TIP3P water model :link(4_7),h4
The TIP3P water model as implemented in CHARMM
"(MacKerell)"_#MacKerell specifies a 3-site rigid water molecule with
charges and Lennard-Jones parameters assigned to each of the 3 atoms.
In LAMMPS the "fix shake"_fix_shake.html command can be used to hold
the two O-H bonds and the H-O-H angle rigid. A bond style of
{harmonic} and an angle style of {harmonic} or {charmm} should also be
used.
These are the additional parameters (in real units) to set for O and H
atoms and the water molecule to run a rigid TIP3P-CHARMM model with a
cutoff. The K values can be used if a flexible TIP3P model (without
fix shake) is desired. If the LJ epsilon and sigma for HH and OH are
set to 0.0, it corresponds to the original 1983 TIP3P model
"(Jorgensen)"_#Jorgensen.
O mass = 15.9994
H mass = 1.008 :all(b),p
O charge = -0.834
H charge = 0.417 :all(b),p
LJ epsilon of OO = 0.1521
LJ sigma of OO = 3.1507
LJ epsilon of HH = 0.0460
LJ sigma of HH = 0.4000
LJ epsilon of OH = 0.0836
LJ sigma of OH = 1.7753 :all(b),p
K of OH bond = 450
r0 of OH bond = 0.9572 :all(b),p
K of HOH angle = 55
theta of HOH angle = 104.52 :all(b),p
These are the parameters to use for TIP3P with a long-range Coulombic
solver (Ewald or PPPM in LAMMPS), see "(Price)"_#Price for details:
O mass = 15.9994
H mass = 1.008 :all(b),p
O charge = -0.830
H charge = 0.415 :all(b),p
LJ epsilon of OO = 0.102
LJ sigma of OO = 3.188
LJ epsilon, sigma of OH, HH = 0.0 :all(b),p
K of OH bond = 450
r0 of OH bond = 0.9572 :all(b),p
K of HOH angle = 55
theta of HOH angle = 104.52 :all(b),p
:line
4.8 TIP4P water model :link(4_8),h4
The four-point TIP4P rigid water model extends the traditional
three-point TIP3P model by adding an additional site, usually
massless, where the charge associated with the oxygen atom is placed.
This site M is located at a fixed distance away from the oxygen along
the bisector of the HOH bond angle. A bond style of {harmonic} and an
angle style of {harmonic} or {charmm} should also be used.
Currently, only a four-point model for long-range Coulombics is
implemented via the LAMMPS "pair style
lj/cut/coul/long/tip4p"_pair_lj.html. A cutoff version may be added
the future. For both models, the bond lengths and bond angles should
be held fixed using the "fix shake"_fix_shake.html command.
These are the additional parameters (in real units) to set for O and H
atoms and the water molecule to run a rigid TIP4P model with a cutoff
"(Jorgensen)"_#Jorgensen. Note that the OM distance is specified in
the "pair_style"_pair_style.html command, not as part of the pair
coefficients.
O mass = 15.9994
H mass = 1.008 :all(b),p
O charge = -1.040
H charge = 0.520 :all(b),p
r0 of OH bond = 0.9572
theta of HOH angle = 104.52 :all(b),p
OM distance = 0.15 :all(b),p
LJ epsilon of O-O = 0.1550
LJ sigma of O-O = 3.1536
LJ epsilon, sigma of OH, HH = 0.0 :all(b),p
These are the parameters to use for TIP4P with a long-range Coulombic
solver (Ewald or PPPM in LAMMPS):
O mass = 15.9994
H mass = 1.008 :all(b),p
O charge = -1.0484
H charge = 0.5242 :all(b),p
r0 of OH bond = 0.9572
theta of HOH angle = 104.52 :all(b),p
OM distance = 0.1250 :all(b),p
LJ epsilon of O-O = 0.16275
LJ sigma of O-O = 3.16435
LJ epsilon, sigma of OH, HH = 0.0 :all(b),p
:line
4.9 SPC water model :link(4_9),h4
The SPC water model specifies a 3-site rigid water molecule with
charges and Lennard-Jones parameters assigned to each of the 3 atoms.
In LAMMPS the "fix shake"_fix_shake.html command can be used to hold
the two O-H bonds and the H-O-H angle rigid. A bond style of
{harmonic} and an angle style of {harmonic} or {charmm} should also be
used.
These are the additional parameters (in real units) to set for O and H
atoms and the water molecule to run a rigid SPC model with long-range
Coulombics (Ewald or PPPM in LAMMPS).
O mass = 15.9994
H mass = 1.008 :all(b),p
O charge = -0.820
H charge = 0.410 :all(b),p
LJ epsilon of OO = 0.1553
LJ sigma of OO = 3.166
LJ epsilon, sigma of OH, HH = 0.0 :all(b),p
r0 of OH bond = 1.0
theta of HOH angle = 109.47 :all(b),p
To use SPC with a long-range Coulombic solver (Ewald or PPPM in
LAMMPS), the only parameters that change are the partial charge
assignments:
O charge = -0.8476
H charge = 0.4238 :all(b),p
:line
4.10 Coupling LAMMPS to other codes :link(4_10),h4
LAMMPS is designed to allow it to be coupled to other codes. For
example, a quantum mechanics code might compute forces on a subset of
atoms and pass those forces to LAMMPS. Or a continuum finite element
(FE) simulation might use atom positions as boundary conditions on FE
nodal points, compute a FE solution, and return interpolated forces on
MD atoms.
LAMMPS can be coupled to other codes in at least 3 ways. Each has
advantages and disadvantages, which you'll have to think about in the
context of your application.
(1) Define a new "fix"_fix.html command that calls the other code. In
this scenario, LAMMPS is the driver code. During its timestepping,
the fix is invoked, and can make library calls to the other code,
which has been linked to LAMMPS as a library. This is the way the
"POEMS"_poems package that performs constrained rigid-body motion on
groups of atoms is hooked to LAMMPS. See the
"fix_poems"_fix_poems.html command for more details. See "this
section"_Section_modify.html of the documentation for info on how to add
a new fix to LAMMPS.
:link(poems,http://www.rpi.edu/~anderk5/lab)
(2) Define a new LAMMPS command that calls the other code. This is
conceptually similar to method (1), but in this case LAMMPS and the
other code are on a more equal footing. Note that now the other code
is not called during the timestepping of a LAMMPS run, but between
runs. The LAMMPS input script can be used to alternate LAMMPS runs
with calls to the other code, invoked via the new command. The
"run"_run.html command facilitates this with its {every} option, which
makes it easy to run a few steps, invoke the command, run a few steps,
invoke the command, etc.
In this scenario, the other code can be called as a library, as in
(1), or it could be a stand-alone code, invoked by a system() call
made by the command (assuming your parallel machine allows one or more
processors to start up another program). In the latter case the
stand-alone code could communicate with LAMMPS thru files that the
command writes and reads.
See "this section"_Section_modify.html of the documentation for how to
add a new command to LAMMPS.
(3) Use LAMMPS as a library called by another code. In this case the
other code is the driver and calls LAMMPS as needed. Or a wrapper
code could link and call both LAMMPS and another code as libraries.
Again, the "run"_run.html command has options that allow it to be
invoked with minimal overhead (no setup or clean-up) if you wish to do
multiple short runs, driven by another program.
"This section"_Section_start.html#2_4 of the documentation describes
how to build LAMMPS as a library. Once this is done, you can
interface with LAMMPS either via C++, C, or Fortran (or any other
language that supports a vanilla C-like interface, e.g. a scripting
language). For example, from C++ you could create one (or more)
"instances" of LAMMPS, pass it an input script to process, or execute
individual commands, all by invoking the correct class methods in
LAMMPS. From C or Fortran you can make function calls to do the same
things. Library.cpp and library.h contain such a C interface with the
functions:
void lammps_open(int, char **, MPI_Comm, void **);
void lammps_close(void *);
void lammps_file(void *, char *);
char *lammps_command(void *, char *); :pre
The functions contain C++ code you could write in a C++ application
that was invoking LAMMPS directly. Note that LAMMPS classes are
defined within a LAMMPS namespace (LAMMPS_NS) if you use them
from another C++ application.
Two of the routines in library.cpp are of particular note. The
lammps_open() function initiates LAMMPS and takes an MPI communicator
as an argument. It returns a pointer to a LAMMPS "object". As with
C++, the lammps_open() function can be called multiple times, to
create multiple instances of LAMMPS.
LAMMPS will run on the set of processors in the communicator. This
means the calling code can run LAMMPS on all or a subset of
processors. For example, a wrapper script might decide to alternate
between LAMMPS and another code, allowing them both to run on all the
processors. Or it might allocate half the processors to LAMMPS and
half to the other code and run both codes simultaneously before
syncing them up periodically.
Library.cpp contains a lammps_command() function to which the caller
passes a single LAMMPS command (a string). Thus the calling code can
read or generate a series of LAMMPS commands (e.g. an input script)
one line at a time and pass it thru the library interface to setup a
problem and then run it.
A few other sample functions are included in library.cpp, but the key
idea is that you can write any functions you wish to define an
interface for how your code talks to LAMMPS and add them to
library.cpp and library.h. The routines you add can access any LAMMPS
data. The examples/couple directory has example C++ and C codes which
show how a stand-alone code can link LAMMPS as a library, run LAMMPS
on a subset of processors, grab data from LAMMPS, change it, and put
it back into LAMMPS.
:line
4.11 Visualizing LAMMPS snapshots :link(4_11),h4
LAMMPS itself does not do visualization, but snapshots from LAMMPS
simulations can be visualized (and analyzed) in a variety of ways.
LAMMPS snapshots are created by the "dump"_dump.html command which can
create files in several formats. The native LAMMPS dump format is a
text file (see "dump atom" or "dump custom") which can be visualized
by the "xmovie"_Section_tools.html#xmovie program, included with the
LAMMPS package. This produces simple, fast 2d projections of 3d
systems, and can be useful for rapid debugging of simulation geometry
and atom trajectories.
Several programs included with LAMMPS as auxiliary tools can convert
native LAMMPS dump files to other formats. See the
"Section_tools"_Section_tools.html doc page for details. The first is
the "ch2lmp tool"_Section_tools.html#charmm, which contains a
lammps2pdb Perl script which converts LAMMPS dump files into PDB
files. The second is the "lmp2arc tool"_Section_tools.html#arc which
converts LAMMPS dump files into Accelrys' Insight MD program files.
The third is the "lmp2cfg tool"_Section_tools.html#cfg which converts
LAMMPS dump files into CFG files which can be read into the
"AtomEye"_atomeye visualizer.
A Python-based toolkit distributed by our group can read native LAMMPS
dump files, including custom dump files with additional columns of
user-specified atom information, and convert them to various formats
or pipe them into visualization software directly. See the "Pizza.py
WWW site"_pizza for details. Specifically, Pizza.py can convert
LAMMPS dump files into PDB, XYZ, "Ensight"_ensight, and VTK formats.
Pizza.py can pipe LAMMPS dump files directly into the Raster3d and
RasMol visualization programs. Pizza.py has tools that do interactive
3d OpenGL visualization and one that creates SVG images of dump file
snapshots.
LAMMPS can create XYZ files directly (via "dump xyz") which is a
simple text-based file format used by many visualization programs
including "VMD"_vmd.
LAMMPS can create DCD files directly (via "dump dcd") which can be
read by "VMD"_vmd in conjunction with a CHARMM PSF file. Using this
form of output avoids the need to convert LAMMPS snapshots to PDB
files. See the "dump"_dump.html command for more information on DCD
files.
LAMMPS can create XTC files directly (via "dump xtc") which is GROMACS
file format which can also be read by "VMD"_vmd for visualization.
See the "dump"_dump.html command for more information on XTC files.
:link(pizza,http://www.cs.sandia.gov/~sjplimp/pizza.html)
:link(vmd,http://www.ks.uiuc.edu/Research/vmd)
:link(ensight,http://www.ensight.com)
:link(atomeye,http://164.107.79.177/Archive/Graphics/A)
:line
4.12 Non-orthogonal simulation boxes :link(4_12),h4
By default, LAMMPS uses an orthogonal simulation box to encompass the
particles. The "boundary"_boundary.html command sets the boundary
conditions of the box (periodic, non-periodic, etc). If the box size
is xprd by yprd by zprd then the 3 mutually orthogonal edge vectors of
an orthogonal simulation box are a = (xprd,0,0), b = (0,yprd,0), and c
= (0,0,zprd).
LAMMPS also allows non-orthogonal simulation boxes (triclinic
symmetry) to be defined with 3 additional "tilt" parameters which
change the edge vectors of the simulation box to be a = (xprd,0,0), b
= (xy,yprd,0), and c = (xz,yz,zprd). The xy, xz, and yz parameters
can be positive or negative. The simulation box must be periodic in
both dimensions associated with a tilt factor. For example, if xz !=
0.0, then the x and z dimensions must be periodic.
To avoid extremely tilted boxes (which would be computationally
inefficient), no tilt factor can skew the box more than half the
distance of the parallel box length, which is the 1st dimension in the
tilt factor (x for xz). For example, if xlo = 2 and xhi = 12, then
the x box length is 10 and the xy tilt factor must be between -5 and
5. Similarly, both xz and yz must be between -(xhi-xlo)/2 and
+(yhi-ylo)/2. Note that this is not a limitation, since if the
maximum tilt factor is 5 (as in this example), then configurations
with tilt = ..., -15, -5, 5, 15, 25, ... are all equivalent.
You tell LAMMPS to use a non-orthogonal box when the simulation box is
defined. This happens in one of 3 ways. If the
"create_box"_create_box.html command is used with a region of style
{prism}, then a non-orthogonal domain is setup. See the
"region"_region.html command for details. If the
"read_data"_read_data.html command is used to define the simulation
box, and the header of the data file contains a line with the "xy xz
yz" keyword, then a non-orthogonal domain is setup. See the
"read_data"_read_data.html command for details. Finally, if the
"read_restart"_read_restart.html command reads a restart file which
was written from a simulation using a triclinic box, then a
non-orthogonal box will be enabled for the restarted simulation.
Note that you can define a non-orthogonal box with all 3 tilt factors
= 0.0, so that it is initially orthogonal. This is necessary if the
box will become non-orthogonal. Alternatively, you can use the
"change_box"_change_box.html command to convert a simulation box from
orthogonal to non-orthogonal and vice versa.
One use of non-orthogonal boxes is to model solid-state crystals with
triclinic symmetry. The "lattice"_lattice.html command can be used
with non-orthogonal basis vectors to define a lattice that will tile a
non-orthogonal simulation box via the "create_atoms"_create_atoms.html
command. Note that while the box edge vectors a,b,c cannot be
arbitrary vectors (e.g. a must be aligned with the x axis), it is
possible to rotate any crystal's basis vectors so that they meet these
restrictions.
A second use of non-orthogonal boxes is to shear a bulk solid to study
the response of the material. The "fix deform"_fix_deform.html
command can be used for this purpose. It allows dynamic control of
the xy, xz, and yz tilt factors as a simulation runs.
Another use of non-orthogonal boxes is to perform non-equilibrium MD
(NEMD) simulations, as discussed in the next section.
:line
4.13 NEMD simulations :link(4_13),h4
Non-equilibrium molecular dynamics or NEMD simulations are typically
used to measure a fluid's rheological properties such as viscosity.
In LAMMPS, such simulations can be performed by first setting up a
non-orthogonal simulation box (see the preceding Howto section).
A shear strain can be applied to the simulation box at a desired
strain rate by using the "fix deform"_fix_deform.html command. The
"fix nvt/sllod"_fix_nvt_sllod.html command can be used to thermostat
the sheared fluid and integrate the SLLOD equations of motion for the
system. Fix nvt/sllod uses "compute
temp/deform"_compute_temp_deform.html to compute a thermal temperature
by subtracting out the streaming velocity of the shearing atoms. The
velocity profile or other properties of the fluid can be monitored via
the "fix ave/spatial"_fix_ave_spatial.html command.
As discussed in the previous section on non-orthogonal simulation
boxes, the amount of tilt or skew that can be applied is limited by
LAMMPS for computational efficiency to be 1/2 of the parallel box
length. However, "fix deform"_fix_deform.html can continuously strain
a box by an arbitrary amount. As discussed in the "fix
deform"_fix_deform.html command, when the tilt value reaches a limit,
the box is re-shaped to the opposite limit which is an equivalent
tiling of periodic space. The strain rate can then continue to change
as before. In a long NEMD simulation these box re-shaping events may
occur many times.
In a NEMD simulation, the "remap" option of "fix
deform"_fix_deform.html should be set to "remap v", since that is what
"fix nvt/sllod"_fix_nvt_sllod.html assumes to generate a velocity
profile consistent with the applied shear strain rate.
An alternative method for calculating viscosities is provided via the
"fix viscosity"_fix_viscosity.html command.
:line
4.14 Extended spherical and aspherical particles :link(4_14),h4
Typical MD models treat atoms or particles as point masses.
Sometimes, however, it is desirable to have a model with finite-size
particles such as spherioids or aspherical ellipsoids. The difference
is that such particles have a moment of inertia, rotational energy,
and angular momentum. Rotation is induced by torque from interactions
with other particles.
LAMMPS has several options for running simulations with these kinds of
particles. The following aspects are discussed in turn:
atom styles
pair potentials
time integration
computes, thermodynamics, and dump output
rigid bodies composed of extended particles :ul
Atom styles :h5
There are 3 "atom styles"_atom_style.html that allow for definition of
finite-size particles: granular, dipole, ellipsoid.
Granular particles are spheriods and each particle can have a unique
diameter and mass (or density). These particles store an angular
velocity (omega) and can be acted upon by torque.
Dipolar particles are typically spheriods with a point dipole and each
particle type has a diamater and mass, set by the "shape"_shape.html
and "mass"_mass.html commands. These particles store an angular
velocity (omega) and can be acted upon by torque. They also store an
orientation for the point dipole (mu) which has a length set by the
"dipole"_dipole.html command. The "set"_set.html command can be used
to initialize the orientation of dipole moments.
Ellipsoid particles are aspherical. Each particle type has an
ellipsoidal shape and mass, defined by the "shape"_shape.html and
"mass"_mass.html commands. These particles store an angular momentum
and their orientation (quaternion), and can be acted upon by torque.
They do not store an angular velocity (omega), which can be in a
different direction than angular momentum, rather they compute it as
needed. Ellipsoidal particles can also store a dipole moment if an
"atom_style hybrid ellipsoid dipole"_atom_style.html is used. The
"set"_set.html command can be used to initialize the orientation of
ellipsoidal particles and has a brief explanation of quaternions.
Note that if one of these atom styles is used (or multiple styles via
the "atom_style hybrid"_atom_style.html command), not all particles in
the system are required to be finite-size or aspherical. For example,
if the 3 shape parameters are set to the same value, the particle will
be a spheroid rather than an ellipsoid. If the 3 shape parameters are
all set to 0.0 or if the diameter is set to 0.0, it will be a point
particle. If the dipole moment is set to zero, the particle will not
have a point dipole associated with it. The pair styles used to
compute pairwise interactions will typically compute the correct
interaction in these simplified (cheaper) cases. "Pair_style
hybrid"_pair_hybrid.html can be used to insure the correct
interactions are computed for the appropriate style of interactions.
Likewise, using groups to partition particles (ellipsoid versus
spheroid versus point particles) will allow you to use the appropriate
time integrators and temperature computations for each class of
particles. See the doc pages for various commands for details.
Also note that for "2d simulations"_dimension.html, finite-size
spheroids and ellipsoids are still treated as 3d particles, rather
than as disks or ellipses. This means they have the same moment of
inertia for a 3d extended object. When their temperature is
coomputed, the correct degrees of freedom are used for rotation in a
2d versus 3d system.
Pair potentials :h5
When a system with extended particles is defined, the particles will
only rotate and experience torque if the force field computes such
interactions. These are the various "pair styles"_pair_style.html
that generate torque:
"pair_style gran/history"_pair_gran.html
"pair_style gran/hertzian"_pair_gran.html
"pair_style gran/no_history"_pair_gran.html
"pair_style dipole/cut"_pair_dipole.html
"pair_style gayberne"_pair_gayberne.html
"pair_style resquared"_pair_resuared.html
"pair_style lubricate"_pair_lubricate.html :ul
The "granular pair styles"_pair_gran.html are used with "atom_style
granular"_atom_style.html. The "dipole pair style"_pair_dipole.html
is used with "atom_style dipole"_atom_style.html. The
"GayBerne"_pair_gayberne.html and "REsquared"_pair_resquared.html
potentials require particles have a "shape"_shape.html and are
designed for "ellipsoidal particles"_atom_style.html. The
"lubrication potential"_pair_lubricate.html requires that particles
have a "shape"_shape.html. It can currently only be used with
extended spherical particles.
Time integration :h5
There are 3 fixes that perform time integration on extended spherical
particles, meaning the integrators update the rotational orientation
and angular velocity or angular momentum of the particles:
"fix nve/sphere"_fix_nve_sphere.html
"fix nvt/sphere"_fix_nvt_sphere.html
"fix npt/sphere"_fix_npt_sphere.html :ul
Likewise, there are 3 fixes that perform time integration on extended
aspherical particles:
"fix nve/asphere"_fix_nve_asphere.html
"fix nvt/asphere"_fix_nvt_asphere.html
"fix npt/asphere"_fix_npt_asphere.html :ul
The advantage of these fixes is that those which thermostat the
particles include the rotational degrees of freedom in the temperature
calculation and thermostatting. Other thermostats can be used with
fix nve/sphere or fix nve/asphere, such as fix langevin or fix
temp/berendsen, but those thermostats only operate on the
translational kinetic energy of the extended particles.
Note that for mixtures of point and extended particles, you should
only use these integration fixes on "groups"_group.html which contain
extended particles.
Computes, thermodynamics, and dump output :h5
There are 4 computes that calculate the temperature or rotational energy
of extended spherical or aspherical particles:
"compute temp/sphere"_compute_temp_sphere.html
"compute temp/asphere"_compute_temp_asphere.html
"compute erotate/sphere"_compute_erotate_sphere.html
"compute erotate/asphere"_compute_erotate_asphere.html :ul
These include rotational degrees of freedom in their computation. If
you wish the thermodynamic output of temperature or pressure to use
one of these computes (e.g. for a system entirely composed of extended
particles), then the compute can be defined and the
"thermo_modify"_thermo_modify.html command used. Note that by
default thermodynamic quantities will be calculated with a temperature
that only includes translational degrees of freedom. See the
"thermo_style"_thermo_style.html command for details.
The "dump custom"_dump.html command can output various attributes of
extended particles, including the dipole moment (mu), the angular
velocity (omega), the angular momentum (angmom), the quaternion
(quat), and the torque (tq) on the particle.
Rigid bodies composed of extended particles :h5
The "fix rigid"_fix_rigid.html command treats a collection of
particles as a rigid body, computes its inertia tensor, sums the total
force and torque on the rigid body each timestep due to forces on its
constituent particles, and integrates the motion of the rigid body.
(NOTE: the feature described in the following paragraph has not yet
been released. It will be soon.)
If any of the constituent particles of a rigid body are extended
particles (spheroids or ellipsoids), then their contribution to the
inertia tensor of the body is different than if they were point
particles. This means the rotational dynamics of the rigid body will
be different. Thus a model of a dimer is different if the dimer
consists of two point masses versus two extended sphereoids, even if
the two particles have the same mass. Extended particles that
experience torque due to their interaction with other particles will
also impart that torque to a rigid body they are part of.
See the "fix rigid" command for example of complex rigid-body models
it is possible to define in LAMMPS.
Note that the "fix shake"_fix_shake.html command can also be used to
treat 2, 3, or 4 particles as a rigid body, but it always assumes the
particles are point masses.
:line
4.15 Output from LAMMPS (thermo, dumps, computes, fixes, variables) :link(4_15),h4
There are four basic kinds of LAMMPS output:
"Thermodynamic output"_thermo_style.html, which is a list
of quantities printed every few timesteps to the screen and logfile. :ulb,l
"Dump files"_dump.html, which contain snapshots of atoms and various
per-atom values and are written at a specified frequency. :l
Certain fixes can output user-specified quantities to files: "fix
ave/time"_fix_ave_time.html for time averaging, "fix
ave/spatial"_fix_ave_spatial.html for spatial averaging, and "fix
print"_fix_print.html for single-line output of
"variables"_variable.html. Fix print can also output to the
screen. :l
"Restart files"_restart.html. :l,ule
A simulation prints one set of thermodynamic output and (optionally)
restart files. It can generate any number of dump files and fix
output files, depending on what "dump"_dump.html and "fix"_fix.html
commands you specify.
As discussed below, LAMMPS gives you a variety of ways to determine
what quantities are computed and printed when the thermodynamics,
dump, or fix commands listed above perform output. Throughout this
discussion, note that users can also "add their own computes and fixes
to LAMMPS"_Section_modify.html which can then generate values that can
then be output with these commands.
The following sub-sections discuss different LAMMPS command related
to output and the kind of data they operate on and produce:
"Global/per-atom/local data"_#global
"Scalar/vector/array data"_#scalar
"Thermodynamic output"_#thermo
"Dump file output"_#dump
"Fixes that write output files"_#fixoutput
"Computes that process output quantities"_#computeoutput
"Fixes that process output quantities"_#fixoutput
"Computes that generate values to output"_#compute
"Fixes that generate values to output"_#fix
"Variables that generate values to output"_#variable
"Summary table of output options and data flow between commands"_#table :ul
Global/per-atom/local data :h5,link(global)
Various output-related commands work with three different styles of
data: global, per-atom, or local. A global datum is one or more
system-wide values, e.g. the temperature of the system. A per-atom
datum is one or more values per atom, e.g. the kinetic energy of each
atom. Local datums are calculated by each processor based on the
atoms it owns, but there may be zero or more per atom, e.g. a list of
bond distances.
Scalar/vector/array data :h5,link(scalar)
Global, per-atom, and local datums can each come in three kinds: a
single scalar value, a vector of values, or a 2d array of values. The
doc page for a "compute" or "fix" or "variable" that generates data
will specify both the style and kind of data it produces, e.g. a
per-atom vector.
When a quantity is accessed, as in many of the output commands
discussed below, it can be referenced via the following bracket
notation, where ID in this case is the ID of a compute. The leading
"c_" would be replaced by "f_" for a fix, or "v_" for a variable:
c_ID | entire scalar, vector, or array
c_ID\[I\] | one element of vector, one column of array
c_ID\[I\]\[J\] | one element of array :tb(s=|)
In other words, using one bracket reduces the dimension of the data
once (vector -> scalar, array -> vector). Using two brackets reduces
the dimension twice (array -> scalar). Thus a command that uses
scalar values as input can typically also process elements of a vector
or array.
Thermodynamic output :h5,link(thermo)
The frequency and format of thermodynamic output is set by the
"thermo"_thermo.html, "thermo_style"_thermo_style.html, and
"thermo_modify"_thermo_modify.html commands. The
"thermo_style"_thermo_style.html command also specifies what values
are calculated and written out. Pre-defined keywords can be specified
(e.g. press, etotal, etc). Three additional kinds of keywords can
also be specified (c_ID, f_ID, v_name), where a "compute"_compute.html
or "fix"_fix.html or "variable"_variable.html provides the value to be
output. In each case, the compute, fix, or variable must generate
global values for input to the "thermo_style custom"_dump.html
command.
Dump file output :h5,link(dump)
Dump file output is specified by the "dump"_dump.html and
"dump_modify"_dump_modify.html commands. There are several
pre-defined formats (dump atom, dump xtc, etc).
There is also a "dump custom"_dump.html format where the user
specifies what values are output with each atom. Pre-defined atom
attributes can be specified (id, x, fx, etc). Three additional kinds
of keywords can also be specified (c_ID, f_ID, v_name), where a
"compute"_compute.html or "fix"_fix.html or "variable"_variable.html
provides the values to be output. In each case, the compute, fix, or
variable must generate per-atom values for input to the "dump
custom"_dump.html command.
There is also a "dump local"_dump.html format where the user specifies
what local values to output. A pre-defined index keyword can be
specified to enumuerate the local values. Two additional kinds of
keywords can also be specified (c_ID, f_ID), where a
"compute"_compute.html or "fix"_fix.html or "variable"_variable.html
provides the values to be output. In each case, the compute or fix
must generate local values for input to the "dump local"_dump.html
command.
Fixes that write output files :h5,link(fixoutput)
Three fixes take various quantities as input and can write output
files: "fix ave/time"_fix_ave_time.html, "fix
ave/spatial"_fix_ave_spatial.html, and "fix print"_fix_print.html.
The "fix ave/time"_fix_ave_time.html command enables direct output to
a file and/or time-averaging of global scalars or vectors. The user
specifies one or more quantities as input. These can be global
"compute"_compute.html values, global "fix"_fix.html values, or
"variables"_variable.html of any style except the atom style which
produces per-atom values. Since a variable can refer to keywords used
by the "thermo_style custom"_thermo_style.html command (like temp or
press) and individual per-atom values, a wide variety of quantities
can be time averaged and/or output in this way. If the inputs are one
or more scalar values, then the fix generate a global scalar or vector
of output. If the inputs are one or more vector values, then the fix
generates a global vector or array of output. The time-averaged
output of this fix can also be used as input to other output commands.
The "fix ave/spatial"_fix_ave_spatial.html command enables direct
output to a file of spatial-averaged per-atom quantities like those
output in dump files, within 1d layers of the simulation box. The
per-atom quantities can be atom density (mass or number) or atom
attributes such as position, velocity, force. They can also be
per-atom quantities calculated by a "compute"_compute.html, by a
"fix"_fix.html, or by an atom-style "variable"_variable.html. The
spatial-averaged output of this fix can also be used as input to other
output commands.
The "fix ave/histo"_fix_ave_histo.html command enables direct output
to a file of histogrammed quantities, which can be global or per-atom
or local quantities. The histogram output of this fix can also be
used as input to other output commands.
The "fix print"_fix_print.html command can generate a line of output
written to the screen and log file or to a separate file, periodically
during a running simulation. The line can contain one or more
"variable"_variable.html values for any style variable except the atom
style). As explained above, variables themselves can contain
references to global values generated by "thermodynamic
keywords"_thermo_style.html, "computes"_compute.html,
"fixes"_fix.html, or other "variables"_variable.html, or to per-atom
values for a specific atom. Thus the "fix print"_fix_print.html
command is a means to output a wide variety of quantities separate
from normal thermodynamic or dump file output.
Computes that process output quantities :h5,link(computeoutput)
The "compute reduce"_compute_reduce.html and "compute
reduce/region"_compute_reduce.html commands take one or more vector
quantities as inputs and "reduce" them (sum, min, max, ave) to scalar
quantities. These are produced as output values which can be used as
input to other output commands.
The "compute property/atom"_compute_property_atom.html command takes a
list of one or more pre-defined atom attributes (id, x, fx, etc) and
stores the values in a per-atom vector or array. These are produced
as output values which can be used as input to other output commands.
The list of atom attributes is the same as for the "dump
custom"_dump.html command.
The "compute property/local"_compute_property_local.html command takes
a list of one or more pre-defined local attributes (bond info, angle
info, etc) and stores the values in a local vector or array. These
are produced as output values which can be used as input to other
output commands.
Fixes that process output quantities :h5,link(fixoutput)
The "fix ave/atom"_fix_ave_atom.html command performs time-averaging
of per-atom vectors. The per-atom quantities can be atom attributes
such as position, velocity, force. They can also be per-atom
quantities calculated by a "compute"_compute.html, by a
"fix"_fix.html, or by an atom-style "variable"_variable.html. The
time-averaged per-atom output of this fix can be used as input to
other output commands.
Computes that generate values to output :h5,link(compute)
Every "compute"_compute.html in LAMMPS produces either global or
per-atom or local values. The values can be scalars or vectors or
arrays of data. These values can be output using the other commands
described in this section. The doc page for each compute command
describes what it produces. Computes that produce per-atom or local
values have the word "atom" or "local" in their style name. Computes
without the word "atom" or "local" produce global values.
Fixes that generate values to output :h5,link(fix)
Some "fixes"_fix.html in LAMMPS produces either global or per-atom or
local values which can be accessed by other commands. The values can
be scalars or vectors or arrays of data. These values can be output
using the other commands described in this section. The doc page for
each fix command tells whether it produces any output quantities and
describes them.
Variables that generate values to output :h5,link(variable)
Every "variables"_variable.html defined in an input script generates
either a global scalar value or a per-atom vector (only atom-style
variables) when it is accessed. The formulas used to define equal-
and atom-style variables can contain references to the thermodynamic
keywords and to global and per-atom data generated by computes, fixes,
and other variables. The values generated by variables can be output
using the other commands described in this section.
Summary table of output options and data flow between commands :h5,link(table)
This table summarizes the various commands that can be used for
generating output from LAMMPS. Each command produces output data of
some kind and/or writes data to a file. Most of the commands can take
data from other commands as input. Thus you can link many of these
commands together in pipeline form, where data produced by one command
is used as input to another command and eventually written to the
screen or to a file. Note that to hook two commands together the
output and input data types must match, e.g. global/per-atom/local
data and scalar/vector/array data.
Also note that, as described above, when a command takes a scalar as
input, that could be an element of a vector or array. Likewise a
vector input could be a column of an array.
Command: Input: Output:
"thermo_style custom"_thermo_style.html: global scalars: screen, log file:
"dump custom"_dump.html: per-atom vectors: dump file:
"dump local"_dump.html: local vectors: dump file:
"fix print"_fix_print.html: global scalar from variable: screen, file:
"print"_print.html: global scalar from variable: screen:
"computes"_compute.html: N/A: global/per-atom/local scalar/vector/array:
"fixes"_fix.html: N/A: global/per-atom/local scalar/vector/array:
"variables"_variable.html: global scalars, per-atom vectors: global scalar, per-atom vector:
"compute reduce"_compute_reduce.html: global/per-atom/local vectors: global scalar/vector:
"compute property/atom"_compute_property_atom.html: per-atom vectors: per-atom vector/array:
"compute property/local"_compute_property_local.html: local vectors: local vector/array:
"fix ave/atom"_fix_ave_atom.html: per-atom vectors: per-atom vector/array:
"fix ave/time"_fix_ave_time.html: global scalars/vectors: global scalar/vector/array, file:
"fix ave/spatial"_fix_ave_spatial.html: per-atom vectors: global array, file:
"fix ave/histo"_fix_ave_histo.html: global/per-atom/local scalars and vectors: global array, file:
:tb(s=:)
:line
4.16 Thermostatting, barostatting, and computing temperature :link(4_16),h4
Thermostatting means controlling the temperature of particles in an MD
simulation. Barostatting means controlling the pressure. Since the
pressure includes a kinetic component due to particle velocities, both
these operations require calculation of the temperature. Typically a
target temperature (T) and/or pressure (P) is specified by the user,
and the thermostat or barostat attempts to equilibrate the system to
the requested T and/or P.
Temperature is computed as kinetic energy divided by some number of
degrees of freedom (and the Boltzmann constant). Since kinetic energy
is a function of particle velocity, there is often a need to
distinguish between a particle's advection velocity (due to some
aggregate motiion of particles) and its thermal velocity. The sum of
the two is the particle's total velocity, but the latter is often what
is wanted to compute a temperature.
LAMMPS has several options for computing temperatures, any of which
can be used in thermostatting and barostatting. These "compute
commands"_compute.html calculate temperature, and the "compute
pressure"_compute_pressure.html command calculates pressure.
"compute temp"_compute_temp.html
"compute temp/sphere"_compute_temp_sphere.html
"compute temp/asphere"_compute_temp_asphere.html
"compute temp/com"_compute_temp_com.html
"compute temp/deform"_compute_temp_deform.html
"compute temp/partial"_compute_temp_partial.html
"compute temp/profile"_compute_temp_profile.html
"compute temp/ramp"_compute_temp_ramp.html
"compute temp/region"_compute_temp_region.html :ul
All but the first 3 calculate velocity biases (i.e. advection
velocities) that are removed when computing the thermal temperature.
"Fix temp/sphere"_fix_temp_sphere.html and "fix
temp/asphere"_fix_temp_asphere.html compute kinetic energy for
extended particles that includes rotational degrees of freedom. They
both allow, as an extra argument, which is another temperature compute
that subtracts a velocity bias. This allows the translational
velocity of extended spherical or aspherical particles to be adjusted
in prescribed ways.
-Thermostatting in LAMMPS is performed by "fixes"_fix.html. Four
-thermostatting fixes are currently available: Nose-Hoover (nvt),
-Berendsen, Langevin, and direct rescaling (temp/rescale):
+Thermostatting in LAMMPS is performed by "fixes"_fix.html, or in one
+case by a pair style. Four thermostatting fixes are currently
+available: Nose-Hoover (nvt), Berendsen, Langevin, and direct
+rescaling (temp/rescale). Dissipative particle dynamics (DPD)
+thermostatting can be invoked via the {dpd/tstat} pair style:
"fix nvt"_fix_nh.html
"fix nvt/sphere"_fix_nvt_sphere.html
"fix nvt/asphere"_fix_nvt_asphere.html
"fix nvt/sllod"_fix_nvt_sllod.html
"fix temp/berendsen"_fix_temp_berendsen.html
"fix langevin"_fix_langevin.html
-"fix temp/rescale"_fix_temp_rescale.html :ul
+"fix temp/rescale"_fix_temp_rescale.html
+"pair_style dpd/tstat"_pair_dpd.html :ul
"Fix nvt"_fix_nh.html only thermostats the translational velocity of
particles. "Fix nvt/sllod"_fix_nvt_sllod.html also does this, except
that it subtracts out a velocity bias due to a deforming box and
integrates the SLLOD equations of motion. See the "NEMD
simulations"_#4_13 section of this page for further details. "Fix
nvt/sphere"_fix_nvt_sphere.html and "fix
nvt/asphere"_fix_nvt_asphere.html thermostat not only translation
velocities but also rotational velocities for spherical and aspherical
particles.
-Any of these fixes can use temperature computes that remove bias for
-two purposes: (a) computing the current temperature to compare to the
-requested target temperature, and (b) adjusting only the thermal
-temperature component of the particle's velocities. See the doc pages
-for the individual fixes and for the "fix_modify"_fix_modify.html
-command for instructions on how to assign a temperature compute to a
-thermostatting fix. For example, you can apply a thermostat to only
-the x and z components of velocity by using it in conjunction with
-"compute temp/partial"_compute_temp_partial.html.
+DPD thermostatting alters pairwise interactions in a manner analagous
+to the per-particle thermostatting of "fix
+langevin"_fix_langevin.html.
+
+Any of the thermostatting fixes can use temperature computes that
+remove bias for two purposes: (a) computing the current temperature to
+compare to the requested target temperature, and (b) adjusting only
+the thermal temperature component of the particle's velocities. See
+the doc pages for the individual fixes and for the
+"fix_modify"_fix_modify.html command for instructions on how to assign
+a temperature compute to a thermostatting fix. For example, you can
+apply a thermostat to only the x and z components of velocity by using
+it in conjunction with "compute
+temp/partial"_compute_temp_partial.html.
IMPORTANT NOTE: Only the nvt fixes perform time integration, meaning
they update the velocities and positions of particles due to forces
and velocities respectively. The other thermostat fixes only adjust
velocities; they do NOT perform time integration updates. Thus they
should be used in conjunction with a constant NVE integration fix such
as these:
"fix nve"_fix_nve.html
"fix nve/sphere"_fix_nve_sphere.html
"fix nve/asphere"_fix_nve_asphere.html :ul
Barostatting in LAMMPS is also performed by "fixes"_fix.html. Two
barosttating methods are currently available: Nose-Hoover (npt and
nph) and Berendsen:
"fix npt"_fix_nh.html
"fix npt/sphere"_fix_npt_sphere.html
"fix npt/asphere"_fix_npt_asphere.html
"fix nph"_fix_nh.html
"fix press/berendsen"_fix_press_berendsen.html :ul
The "fix npt"_fix_nh.html commands include a Nose-Hoover thermostat
and barostat. "Fix nph"_fix_nh.html is just a Nose/Hoover barostat;
it does no thermostatting. Both "fix nph"_fix_nh.html and "fix
press/bernendsen"_fix_press_berendsen.html can be used in conjunction
with any of the thermostatting fixes.
As with the thermostats, "fix npt"_fix_nh.html and "fix
nph"_fix_nh.html only use translational motion of the particles in
computing T and P and performing thermo/barostatting. "Fix
npt/sphere"_fix_npt_sphere.html and "fix
npt/asphere"_fix_npt_asphere.html thermo/barostat using not only
translation velocities but also rotational velocities for spherical
and aspherical particles.
All of the barostatting fixes use the "compute
pressure"_compute_pressure.html compute to calculate a current
pressure. By default, this compute is created with a simple "compute
temp"_compute_temp.html (see the last argument of the "compute
pressure"_compute_pressure.html command), which is used to calculated
the kinetic componenet of the pressure. The barostatting fixes can
also use temperature computes that remove bias for the purpose of
computing the kinetic componenet which contributes to the current
pressure. See the doc pages for the individual fixes and for the
"fix_modify"_fix_modify.html command for instructions on how to assign
a temperature or pressure compute to a barostatting fix.
IMPORTANT NOTE: As with the thermostats, the Nose/Hoover methods ("fix
npt"_fix_nh.html and "fix nph"_fix_nh.html) perform time
integration. "Fix press/berendsen"_fix_press_berendsen.html does NOT,
so it should be used with one of the constant NVE fixes or with one of
the NVT fixes.
Finally, thermodynamic output, which can be setup via the
"thermo_style"_thermo_style.html command, often includes temperature
and pressure values. As explained on the doc page for the
"thermo_style"_thermo_style.html command, the default T and P are
setup by the thermo command itself. They are NOT the ones associated
with any thermostatting or barostatting fix you have defined or with
any compute that calculates a temperature or pressure. Thus if you
want to view these values of T and P, you need to specify them
explicitly via a "thermo_style custom"_thermo_style.html command. Or
you can use the "thermo_modify"_thermo_modify.html command to
re-define what temperature or pressure compute is used for default
thermodynamic output.
:line
4.16 Walls :link(4_17),h4
Walls in an MD simulation are typically used to bound particle motion,
i.e. to serve as a boundary condition.
Walls in LAMMPS can be of rough (made of particles) or idealized
surfaces. Ideal walls can be smooth, generating forces only in the
normal direction, or frictional, generating forces also in the
tangential direction.
Rough walls, built of particles, can be created in various ways. The
particles themselves can be generated like any other particle, via the
"lattice"_lattice.html and "create_atoms"_create_atoms.html commands,
or read in via the "read_data"_read_data.html command.
Their motion can be constrained by many different commands, so that
they do not move at all, move together as a group at constant velocity
or in response to a net force acting on them, move in a prescribed
fashion (e.g. rotate around a point), etc. Note that if a time
integration fix like "fix nve"_fix_nve.html or "fix nvt"_fix_nh.html
is not used with the group that contains wall particles, their
positions and velocities will not be updated.
"fix aveforce"_fix_aveforce.html - set force on particles to average value, so they move together
"fix setforce"_fix_setforce.html - set force on particles to a value, e.g. 0.0
"fix freeze"_fix_freeze.html - freeze particles for use as granular walls
"fix nve/noforce"_fix_nve_noforce.html - advect particles by their velocity, but without force
"fix move"_fix_move.html - prescribe motion of particles by a linear velocity, oscillation, rotation, variable :ul
The "fix move"_fix_move.html command offers the most generality, since
the motion of individual particles can be specified with
"variable"_variable.html formula which depends on time and/or the
particle position.
For rough walls, it may be useful to turn off pairwise interactions
between wall particles via the "neigh_modify
exclude"_neigh_modify.html command.
Rough walls can also be created by specifying frozen particles that do
not move and do not interact with mobile particles, and then tethering
other particles to the fixed particles, via a "bond"_bond_style.html.
The bonded particles do interact with other mobile particles.
Idealized walls can be specified via several fix commands. "Fix
wall/gran"_fix_wall_gran.html creates frictional walls for use with
granular particles; all the other commands create smooth walls.
"fix wall/reflect"_fix_wall_reflect.html - reflective flat walls
"fix wall/lj93"_fix_wall.html - flat walls, with Lennard-Jones 9/3 potential
"fix wall/lj126"_fix_wall.html - flat walls, with Lennard-Jones 12/6 potential
"fix wall/colloid"_fix_wall.html - flat walls, with "pair_style colloid"_pair_colloid.html potential
"fix wall/harmonic"_fix_wall.html - flat walls, with repulsive harmonic spring potential
"fix wall/region"_fix_wall_region.html - use region surface as wall
"fix wall/gran"_fix_wall_gran.html - flat or curved walls with "pair_style granular"_pair_gran.html potential :ul
The {lj93}, {lj126}, {colloid}, and {harmonic} styles all allow the
flat walls to move with a constant velocity, or oscillate in time.
The "fix wall/region"_fix_wall_region.html command offers the most
generality, since the region surface is treated as a wall, and the
geometry of the region can be a simple primitive volume (e.g. a
sphere, or cube, or plane), or a complex volume made from the union
and intersection of primitive volumes. "Regions"_region.html can also
specify a volume "interior" or "exterior" to the specified primitive
shape or {union} or {intersection}. "Regions"_region.html can also be
"dynamic" meaning they move with constant velocity, oscillate, or
rotate.
The only frictional idealized walls currently in LAMMPS are flat or
curved surfaces specified by the "fix wall/gran"_fix_wall_gran.html
command. At some point we plan to allow regoin surfaces to be used as
frictional walls, as well as triangulated surfaces.
:line
:line
:link(Cornell)
[(Cornell)] Cornell, Cieplak, Bayly, Gould, Merz, Ferguson,
Spellmeyer, Fox, Caldwell, Kollman, JACS 117, 5179-5197 (1995).
:link(Horn)
[(Horn)] Horn, Swope, Pitera, Madura, Dick, Hura, and Head-Gordon,
J Chem Phys, 120, 9665 (2004).
:link(MacKerell)
[(MacKerell)] MacKerell, Bashford, Bellott, Dunbrack, Evanseck, Field,
Fischer, Gao, Guo, Ha, et al, J Phys Chem, 102, 3586 (1998).
:link(Jorgensen)
[(Jorgensen)] Jorgensen, Chandrasekhar, Madura, Impey, Klein, J Chem
Phys, 79, 926 (1983).
:link(Price)
[(Price)] Price and Brooks, J Chem Phys, 121, 10096 (2004).
diff --git a/doc/Section_tools.html b/doc/Section_tools.html
index 59cf12fd9..f4fb38d1b 100644
--- a/doc/Section_tools.html
+++ b/doc/Section_tools.html
@@ -1,371 +1,370 @@
<HTML>
<CENTER><A HREF = "Section_perf.html">Previous Section</A> - <A HREF = "http://lammps.sandia.gov">LAMMPS WWW Site</A> - <A HREF = "Manual.html">LAMMPS
Documentation</A> - <A HREF = "Section_commands.html#comm">LAMMPS Commands</A> - <A HREF = "Section_modify.html">Next
Section</A>
</CENTER>
<HR>
<H3>7. Additional tools
</H3>
<P>LAMMPS is designed to be a computational kernel for performing
molecular dynamics computations. Additional pre- and post-processing
steps are often necessary to setup and analyze a simulation. A few
additional tools are provided with the LAMMPS distribution and are
described in this section.
</P>
<P>Our group has also written and released a separate toolkit called
<A HREF = "http://www.cs.sandia.gov/~sjplimp/pizza.html">Pizza.py</A> which provides tools for doing setup, analysis,
plotting, and visualization for LAMMPS simulations. Pizza.py is
written in <A HREF = "http://www.python.org">Python</A> and is available for download from <A HREF = "http://www.cs.sandia.gov/~sjplimp/pizza.html">the
Pizza.py WWW site</A>.
</P>
<P>Note that many users write their own setup or analysis tools or use
other existing codes and convert their output to a LAMMPS input format
or vice versa. The tools listed here are included in the LAMMPS
distribution as examples of auxiliary tools. Some of them are not
actively supported by Sandia, as they were contributed by LAMMPS
users. If you have problems using them, we can direct you to the
authors.
</P>
<P>The source code for each of these codes is in the tools sub-directory
of the LAMMPS distribution. There is a Makefile (which you may need
to edit for your platform) which will build several of the tools which
reside in that directory. Some of them are larger packages in their
own sub-directories with their own Makefiles.
</P>
<UL><LI><A HREF = "#amber">amber2lmp</A>
<LI><A HREF = "#binary">binary2txt</A>
<LI><A HREF = "#charmm">ch2lmp</A>
<LI><A HREF = "#chain">chain</A>
<LI><A HREF = "#data">data2xmovie</A>
<LI><A HREF = "#eam">eam generate</A>
<LI><A HREF = "#arc">lmp2arc</A>
<LI><A HREF = "#cfg">lmp2cfg</A>
<LI><A HREF = "#traj">lmp2traj</A>
<LI><A HREF = "#vmd">lmp2vmd</A>
<LI><A HREF = "#matlab">matlab</A>
<LI><A HREF = "#micelle">micelle2d</A>
<LI><A HREF = "#msi">msi2lmp</A>
<LI><A HREF = "#pymol">pymol_asphere</A>
<LI><A HREF = "#pythontools">python</A>
<LI><A HREF = "#restart">restart2data</A>
<LI><A HREF = "#thermo_extract">thermo_extract</A>
<LI><A HREF = "#vim">vim</A>
<LI><A HREF = "#xmovie">xmovie</A>
</UL>
<HR>
<H4><A NAME = "amber"></A>amber2lmp tool
</H4>
<P>The amber2lmp sub-directory contains two Python scripts for converting
files back-and-forth between the AMBER MD code and LAMMPS. See the
README file in amber2lmp for more information.
</P>
<P>These tools were written by Keir Novik while he was at Queen Mary
University of London. Keir is no longer there and cannot support
these tools which are out-of-date with respect to the current LAMMPS
version (and maybe with respect to AMBER as well). Since we don't use
these tools at Sandia, you'll need to experiment with them and make
necessary modifications yourself.
</P>
<HR>
<H4><A NAME = "binary"></A>binary2txt tool
</H4>
<P>The file binary2txt.cpp converts one or more binary LAMMPS dump file
into ASCII text files. The syntax for running the tool is
</P>
<PRE>binary2txt file1 file2 ...
</PRE>
<P>which creates file1.txt, file2.txt, etc. This tool must be compiled
on a platform that can read the binary file created by a LAMMPS run,
since binary files are not compatible across all platforms.
</P>
<HR>
<H4><A NAME = "charmm"></A>ch2lmp tool
</H4>
<P>The ch2lmp sub-directory contains tools for converting files
back-and-forth between the CHARMM MD code and LAMMPS.
</P>
<P>They are intended to make it easy to use CHARMM as a builder and as a
post-processor for LAMMPS. Using charmm2lammps.pl, you can convert an
ensemble built in CHARMM into its LAMMPS equivalent. Using
lammps2pdb.pl you can convert LAMMPS atom dumps into pdb files.
</P>
<P>See the README file in the ch2lmp sub-directory for more information.
</P>
<P>These tools were created by Pieter in't Veld (pjintve at sandia.gov)
and Paul Crozier (pscrozi at sandia.gov) at Sandia.
</P>
<HR>
<H4><A NAME = "chain"></A>chain tool
</H4>
<P>The file chain.f creates a LAMMPS data file containing bead-spring
polymer chains and/or monomer solvent atoms. It uses a text file
containing chain definition parameters as an input. The created
chains and solvent atoms can strongly overlap, so LAMMPS needs to run
the system initially with a "soft" pair potential to un-overlap it.
The syntax for running the tool is
</P>
<PRE>chain < def.chain > data.file
</PRE>
<P>See the def.chain or def.chain.ab files in the tools directory for
examples of definition files. This tool was used to create the
system for the <A HREF = "Section_perf.html">chain benchmark</A>.
</P>
<HR>
<H4><A NAME = "data"></A>data2xmovie tool
</H4>
<P>The file data2xmovie.c converts a LAMMPS data file into a snapshot
suitable for visualizing with the <A HREF = "#xmovie">xmovie</A> tool, as if it had
been output with a dump command from LAMMPS itself. The syntax for
running the tool is
</P>
<PRE>data2xmovie <B>options</B> < infile > outfile
</PRE>
<P>See the top of the data2xmovie.c file for a discussion of the options.
</P>
<HR>
<H4><A NAME = "eam"></A>eam generate tool
</H4>
<P>The tools/eam_generate directory contains several one-file C programs
that convert an analytic formula into a tabulated <A HREF = "pair_eam.html">embedded atom
method (EAM)</A> setfl potential file. The potentials they
produce are in the potentials directory.
</P>
<P>The source files and potentials were provided by Gerolf Ziegenhain
(gerolf at ziegenhain.com).
</P>
<HR>
<H4><A NAME = "arc"></A>lmp2arc tool
</H4>
<P>The lmp2arc sub-directory contains a tool for converting LAMMPS output
files to the format for Accelrys' Insight MD code (formerly
MSI/Biosym and its Discover MD code). See the README file for more
information.
</P>
<P>This tool was written by John Carpenter (Cray), Michael Peachey
(Cray), and Steve Lustig (Dupont). John is now at the Mayo Clinic
(jec at mayo.edu), but still fields questions about the tool.
</P>
<P>This tool was updated for the current LAMMPS C++ version by Jeff
Greathouse at Sandia (jagreat at sandia.gov).
</P>
<HR>
<H4><A NAME = "cfg"></A>lmp2cfg tool
</H4>
<P>The lmp2cfg sub-directory contains a tool for converting LAMMPS output
files into a series of *.cfg files which can be read into the
<A HREF = "http://164.107.79.177/Archive/Graphics/A">AtomEye</A> visualizer. See
the README file for more information.
</P>
<P>This tool was written by Ara Kooser at Sandia (askoose at sandia.gov).
</P>
<HR>
<H4><A NAME = "traj"></A>lmp2traj tool
</H4>
<P>The lmp2traj sub-directory contains a tool for converting LAMMPS output
files into 3 analysis files. One file can be used to create contour
maps of the atom positions over the course of the simulation. The
other two files provide density profiles and dipole moments. See the
README file for more information.
</P>
<P>This tool was written by Ara Kooser at Sandia (askoose at sandia.gov).
</P>
<HR>
<H4><A NAME = "vmd"></A>lmp2vmd tool
</H4>
<P>The lmp2vmd sub-directory contains a README.txt file that describes
details of scripts and plugin support within the <A HREF = "http://www.ks.uiuc.edu/Research/vmd">VMD
package</A> for visualizing LAMMPS
dump files.
</P>
<P>The VMD plugins and other supporting scripts were written by Axel
Kohlmeyer (akohlmey at cmm.chem.upenn.edu) at U Penn.
</P>
<HR>
<H4><A NAME = "matlab"></A>matlab tool
</H4>
<P>The matlab sub-directory contains several <A HREF = "http://www.mathworks.com">MATLAB</A> scripts for
post-processing LAMMPS output. The scripts include readers for log
-and dump files, a reader for radial distribution output from the <A HREF = "fix_rdf.html">fix
-rdf</A> command, a reader for EAM potential files, and a
-converter that reads LAMMPS dump files and produces CFG files that can
-be visualized with the
-<A HREF = "http://164.107.79.177/Archive/Graphics/A">AtomEye</A> visualizer.
+and dump files, a reader for EAM potential files, and a converter that
+reads LAMMPS dump files and produces CFG files that can be visualized
+with the <A HREF = "http://164.107.79.177/Archive/Graphics/A">AtomEye</A>
+visualizer.
</P>
<P>See the README.pdf file for more information.
</P>
<P>These scripts were written by Arun Subramaniyan at Purdue Univ
(asubrama at purdue.edu).
</P>
<HR>
<H4><A NAME = "micelle"></A>micelle2d tool
</H4>
<P>The file micelle2d.f creates a LAMMPS data file containing short lipid
chains in a monomer solution. It uses a text file containing lipid
definition parameters as an input. The created molecules and solvent
atoms can strongly overlap, so LAMMPS needs to run the system
initially with a "soft" pair potential to un-overlap it. The syntax
for running the tool is
</P>
<PRE>micelle2d < def.micelle2d > data.file
</PRE>
<P>See the def.micelle2d file in the tools directory for an example of a
definition file. This tool was used to create the system for the
<A HREF = "Section_example.html">micelle example</A>.
</P>
<HR>
<H4><A NAME = "msi"></A>msi2lmp tool
</H4>
<P>The msi2lmp sub-directory contains a tool for creating LAMMPS input
data files from Accelrys' Insight MD code (formerly MSI/Biosym and
its Discover MD code). See the README file for more information.
</P>
<P>This tool was written by John Carpenter (Cray), Michael Peachey
(Cray), and Steve Lustig (Dupont). John is now at the Mayo Clinic
(jec at mayo.edu), but still fields questions about the tool.
</P>
<P>This tool may be out-of-date with respect to the current LAMMPS and
Insight versions. Since we don't use it at Sandia, you'll need to
experiment with it yourself.
</P>
<HR>
<H4><A NAME = "pymol"></A>pymol_asphere tool
</H4>
<P>The pymol_asphere sub-directory contains a tool for converting a
LAMMPS dump file that contains orientation info for ellipsoidal
particles into an input file for the <A HREF = "http://pymol.sourceforge.net">PyMol visualization
package</A>.
</P>
<P>Specifically, the tool triangulates the ellipsoids so they can be
viewed as true ellipsoidal particles within PyMol. See the README and
examples directory within pymol_asphere for more information.
</P>
<P>This tool was written by Mike Brown at Sandia.
</P>
<HR>
<H4><A NAME = "pythontools"></A>python tool
</H4>
<P>The python sub-directory contains several Python scripts
that perform common LAMMPS post-processing tasks, like
</P>
<UL><LI>extract thermodynamic info from a log file as columns of numbers
<LI>plot two columns of thermodynamic info from a log file using GnuPlot
<LI>sort the snapshots in a dump file by atom ID
<LI>convert dump files into XYZ, CFG, or PDB format for viz by other packages
</UL>
<P>These are simple scripts built on <A HREF = "http://www.cs.sandia.gov/~sjplimp/pizza.html">Pizza.py</A> modules. See the
README for more info on Pizza.py and how to use these scripts.
</P>
<HR>
<H4><A NAME = "restart"></A>restart2data tool
</H4>
<P>The file restart2data.cpp converts a binary LAMMPS restart file into
an ASCII data file. The syntax for running the tool is
</P>
<PRE>restart2data restart-file data-file (input-file)
</PRE>
<P>Input-file is optional and if specified will contain LAMMPS input
commands for the masses and force field parameters, instead of putting
those in the data-file. Only a few force field styles currently
support this option.
</P>
<P>This tool must be compiled on a platform that can read the binary file
created by a LAMMPS run, since binary files are not compatible across
all platforms.
</P>
<P>Note that a text data file has less precision than a binary restart
file. Hence, continuing a run from a converted data file will
typically not conform as closely to a previous run as will restarting
from a binary restart file.
</P>
<P>If a "%" appears in the specified restart-file, the tool expects a set
of multiple files to exist. See the <A HREF = "restart.html">restart</A> and
<A HREF = "write_restart.html">write_restart</A> commands for info on how such sets
of files are written by LAMMPS, and how the files are named.
</P>
<HR>
<H4><A NAME = "thermo_extract"></A>thermo_extract tool
</H4>
<P>The thermo_extract tool reads one of more LAMMPS log files and
extracts a thermodynamic value (e.g. Temp, Press). It spits out the
time,value as 2 columns of numbers so the tool can be used as a quick
way to plot some quantity of interest. See the header of the
thermo_extract.c file for the syntax of how to run it and other
details.
</P>
<P>This tool was written by Vikas Varshney at Wright Patterson AFB
(vikas.varshney at gmail.com).
</P>
<HR>
<H4><A NAME = "vim"></A>vim tool
</H4>
<P>The files in the tools/vim directory are add-ons to the VIM editor
that allow easier editing of LAMMPS input scripts. See the README.txt
file for details.
</P>
<P>These files were provided by Gerolf Ziegenhain (gerolf at
ziegenhain.com)
</P>
<HR>
<H4><A NAME = "xmovie"></A>xmovie tool
</H4>
<P>The xmovie tool is an X-based visualization package that can read
LAMMPS dump files and animate them. It is in its own sub-directory
with the tools directory. You may need to modify its Makefile so that
it can find the appropriate X libraries to link against.
</P>
<P>The syntax for running xmovie is
</P>
<PRE>xmovie <B>options</B> dump.file1 dump.file2 ...
</PRE>
<P>If you just type "xmovie" you will see a list of options. Note that
by default, LAMMPS dump files are in scaled coordinates, so you
typically need to use the -scale option with xmovie. When xmovie runs
it opens a visualization window and a control window. The control
options are straightforward to use.
</P>
<P>Xmovie was mostly written by Mike Uttormark (U Wisconsin) while he
spent a summer at Sandia. It displays 2d projections of a 3d domain.
While simple in design, it is an amazingly fast program that can
render large numbers of atoms very quickly. It's a useful tool for
debugging LAMMPS input and output and making sure your simulation is
doing what you think it should. The animations on the Examples page
of the <A HREF = "http://lammps.sandia.gov">LAMMPS WWW site</A> were created with xmovie.
</P>
<P>I've lost contact with Mike, so I hope he's comfortable with us
distributing his great tool!
</P>
</HTML>
diff --git a/doc/Section_tools.txt b/doc/Section_tools.txt
index 1fbf364ba..f3cfb5d77 100644
--- a/doc/Section_tools.txt
+++ b/doc/Section_tools.txt
@@ -1,365 +1,364 @@
"Previous Section"_Section_perf.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc - "Next
Section"_Section_modify.html :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Section_commands.html#comm)
:line
7. Additional tools :h3
LAMMPS is designed to be a computational kernel for performing
molecular dynamics computations. Additional pre- and post-processing
steps are often necessary to setup and analyze a simulation. A few
additional tools are provided with the LAMMPS distribution and are
described in this section.
Our group has also written and released a separate toolkit called
"Pizza.py"_pizza which provides tools for doing setup, analysis,
plotting, and visualization for LAMMPS simulations. Pizza.py is
written in "Python"_python and is available for download from "the
Pizza.py WWW site"_pizza.
:link(pizza,http://www.cs.sandia.gov/~sjplimp/pizza.html)
:link(python,http://www.python.org)
Note that many users write their own setup or analysis tools or use
other existing codes and convert their output to a LAMMPS input format
or vice versa. The tools listed here are included in the LAMMPS
distribution as examples of auxiliary tools. Some of them are not
actively supported by Sandia, as they were contributed by LAMMPS
users. If you have problems using them, we can direct you to the
authors.
The source code for each of these codes is in the tools sub-directory
of the LAMMPS distribution. There is a Makefile (which you may need
to edit for your platform) which will build several of the tools which
reside in that directory. Some of them are larger packages in their
own sub-directories with their own Makefiles.
"amber2lmp"_#amber
"binary2txt"_#binary
"ch2lmp"_#charmm
"chain"_#chain
"data2xmovie"_#data
"eam generate"_#eam
"lmp2arc"_#arc
"lmp2cfg"_#cfg
"lmp2traj"_#traj
"lmp2vmd"_#vmd
"matlab"_#matlab
"micelle2d"_#micelle
"msi2lmp"_#msi
"pymol_asphere"_#pymol
"python"_#pythontools
"restart2data"_#restart
"thermo_extract"_#thermo_extract
"vim"_#vim
"xmovie"_#xmovie :ul
:line
amber2lmp tool :h4,link(amber)
The amber2lmp sub-directory contains two Python scripts for converting
files back-and-forth between the AMBER MD code and LAMMPS. See the
README file in amber2lmp for more information.
These tools were written by Keir Novik while he was at Queen Mary
University of London. Keir is no longer there and cannot support
these tools which are out-of-date with respect to the current LAMMPS
version (and maybe with respect to AMBER as well). Since we don't use
these tools at Sandia, you'll need to experiment with them and make
necessary modifications yourself.
:line
binary2txt tool :h4,link(binary)
The file binary2txt.cpp converts one or more binary LAMMPS dump file
into ASCII text files. The syntax for running the tool is
binary2txt file1 file2 ... :pre
which creates file1.txt, file2.txt, etc. This tool must be compiled
on a platform that can read the binary file created by a LAMMPS run,
since binary files are not compatible across all platforms.
:line
ch2lmp tool :h4,link(charmm)
The ch2lmp sub-directory contains tools for converting files
back-and-forth between the CHARMM MD code and LAMMPS.
They are intended to make it easy to use CHARMM as a builder and as a
post-processor for LAMMPS. Using charmm2lammps.pl, you can convert an
ensemble built in CHARMM into its LAMMPS equivalent. Using
lammps2pdb.pl you can convert LAMMPS atom dumps into pdb files.
See the README file in the ch2lmp sub-directory for more information.
These tools were created by Pieter in't Veld (pjintve at sandia.gov)
and Paul Crozier (pscrozi at sandia.gov) at Sandia.
:line
chain tool :h4,link(chain)
The file chain.f creates a LAMMPS data file containing bead-spring
polymer chains and/or monomer solvent atoms. It uses a text file
containing chain definition parameters as an input. The created
chains and solvent atoms can strongly overlap, so LAMMPS needs to run
the system initially with a "soft" pair potential to un-overlap it.
The syntax for running the tool is
chain < def.chain > data.file :pre
See the def.chain or def.chain.ab files in the tools directory for
examples of definition files. This tool was used to create the
system for the "chain benchmark"_Section_perf.html.
:line
data2xmovie tool :h4,link(data)
The file data2xmovie.c converts a LAMMPS data file into a snapshot
suitable for visualizing with the "xmovie"_#xmovie tool, as if it had
been output with a dump command from LAMMPS itself. The syntax for
running the tool is
data2xmovie [options] < infile > outfile :pre
See the top of the data2xmovie.c file for a discussion of the options.
:line
eam generate tool :h4,link(eam)
The tools/eam_generate directory contains several one-file C programs
that convert an analytic formula into a tabulated "embedded atom
method (EAM)"_pair_eam.html setfl potential file. The potentials they
produce are in the potentials directory.
The source files and potentials were provided by Gerolf Ziegenhain
(gerolf at ziegenhain.com).
:line
lmp2arc tool :h4,link(arc)
The lmp2arc sub-directory contains a tool for converting LAMMPS output
files to the format for Accelrys' Insight MD code (formerly
MSI/Biosym and its Discover MD code). See the README file for more
information.
This tool was written by John Carpenter (Cray), Michael Peachey
(Cray), and Steve Lustig (Dupont). John is now at the Mayo Clinic
(jec at mayo.edu), but still fields questions about the tool.
This tool was updated for the current LAMMPS C++ version by Jeff
Greathouse at Sandia (jagreat at sandia.gov).
:line
lmp2cfg tool :h4,link(cfg)
The lmp2cfg sub-directory contains a tool for converting LAMMPS output
files into a series of *.cfg files which can be read into the
"AtomEye"_http://164.107.79.177/Archive/Graphics/A visualizer. See
the README file for more information.
This tool was written by Ara Kooser at Sandia (askoose at sandia.gov).
:line
lmp2traj tool :h4,link(traj)
The lmp2traj sub-directory contains a tool for converting LAMMPS output
files into 3 analysis files. One file can be used to create contour
maps of the atom positions over the course of the simulation. The
other two files provide density profiles and dipole moments. See the
README file for more information.
This tool was written by Ara Kooser at Sandia (askoose at sandia.gov).
:line
lmp2vmd tool :h4,link(vmd)
The lmp2vmd sub-directory contains a README.txt file that describes
details of scripts and plugin support within the "VMD
package"_http://www.ks.uiuc.edu/Research/vmd for visualizing LAMMPS
dump files.
The VMD plugins and other supporting scripts were written by Axel
Kohlmeyer (akohlmey at cmm.chem.upenn.edu) at U Penn.
:line
matlab tool :h4,link(matlab)
The matlab sub-directory contains several "MATLAB"_matlab scripts for
post-processing LAMMPS output. The scripts include readers for log
-and dump files, a reader for radial distribution output from the "fix
-rdf"_fix_rdf.html command, a reader for EAM potential files, and a
-converter that reads LAMMPS dump files and produces CFG files that can
-be visualized with the
-"AtomEye"_http://164.107.79.177/Archive/Graphics/A visualizer.
+and dump files, a reader for EAM potential files, and a converter that
+reads LAMMPS dump files and produces CFG files that can be visualized
+with the "AtomEye"_http://164.107.79.177/Archive/Graphics/A
+visualizer.
See the README.pdf file for more information.
These scripts were written by Arun Subramaniyan at Purdue Univ
(asubrama at purdue.edu).
:link(matlab,http://www.mathworks.com)
:line
micelle2d tool :h4,link(micelle)
The file micelle2d.f creates a LAMMPS data file containing short lipid
chains in a monomer solution. It uses a text file containing lipid
definition parameters as an input. The created molecules and solvent
atoms can strongly overlap, so LAMMPS needs to run the system
initially with a "soft" pair potential to un-overlap it. The syntax
for running the tool is
micelle2d < def.micelle2d > data.file :pre
See the def.micelle2d file in the tools directory for an example of a
definition file. This tool was used to create the system for the
"micelle example"_Section_example.html.
:line
msi2lmp tool :h4,link(msi)
The msi2lmp sub-directory contains a tool for creating LAMMPS input
data files from Accelrys' Insight MD code (formerly MSI/Biosym and
its Discover MD code). See the README file for more information.
This tool was written by John Carpenter (Cray), Michael Peachey
(Cray), and Steve Lustig (Dupont). John is now at the Mayo Clinic
(jec at mayo.edu), but still fields questions about the tool.
This tool may be out-of-date with respect to the current LAMMPS and
Insight versions. Since we don't use it at Sandia, you'll need to
experiment with it yourself.
:line
pymol_asphere tool :h4,link(pymol)
The pymol_asphere sub-directory contains a tool for converting a
LAMMPS dump file that contains orientation info for ellipsoidal
particles into an input file for the "PyMol visualization
package"_pymol.
:link(pymol,http://pymol.sourceforge.net)
Specifically, the tool triangulates the ellipsoids so they can be
viewed as true ellipsoidal particles within PyMol. See the README and
examples directory within pymol_asphere for more information.
This tool was written by Mike Brown at Sandia.
:line
python tool :h4,link(pythontools)
The python sub-directory contains several Python scripts
that perform common LAMMPS post-processing tasks, like
extract thermodynamic info from a log file as columns of numbers
plot two columns of thermodynamic info from a log file using GnuPlot
sort the snapshots in a dump file by atom ID
convert dump files into XYZ, CFG, or PDB format for viz by other packages :ul
These are simple scripts built on "Pizza.py"_pizza modules. See the
README for more info on Pizza.py and how to use these scripts.
:line
restart2data tool :h4,link(restart)
The file restart2data.cpp converts a binary LAMMPS restart file into
an ASCII data file. The syntax for running the tool is
restart2data restart-file data-file (input-file) :pre
Input-file is optional and if specified will contain LAMMPS input
commands for the masses and force field parameters, instead of putting
those in the data-file. Only a few force field styles currently
support this option.
This tool must be compiled on a platform that can read the binary file
created by a LAMMPS run, since binary files are not compatible across
all platforms.
Note that a text data file has less precision than a binary restart
file. Hence, continuing a run from a converted data file will
typically not conform as closely to a previous run as will restarting
from a binary restart file.
If a "%" appears in the specified restart-file, the tool expects a set
of multiple files to exist. See the "restart"_restart.html and
"write_restart"_write_restart.html commands for info on how such sets
of files are written by LAMMPS, and how the files are named.
:line
thermo_extract tool :h4,link(thermo_extract)
The thermo_extract tool reads one of more LAMMPS log files and
extracts a thermodynamic value (e.g. Temp, Press). It spits out the
time,value as 2 columns of numbers so the tool can be used as a quick
way to plot some quantity of interest. See the header of the
thermo_extract.c file for the syntax of how to run it and other
details.
This tool was written by Vikas Varshney at Wright Patterson AFB
(vikas.varshney at gmail.com).
:line
vim tool :h4,link(vim)
The files in the tools/vim directory are add-ons to the VIM editor
that allow easier editing of LAMMPS input scripts. See the README.txt
file for details.
These files were provided by Gerolf Ziegenhain (gerolf at
ziegenhain.com)
:line
xmovie tool :h4,link(xmovie)
The xmovie tool is an X-based visualization package that can read
LAMMPS dump files and animate them. It is in its own sub-directory
with the tools directory. You may need to modify its Makefile so that
it can find the appropriate X libraries to link against.
The syntax for running xmovie is
xmovie [options] dump.file1 dump.file2 ... :pre
If you just type "xmovie" you will see a list of options. Note that
by default, LAMMPS dump files are in scaled coordinates, so you
typically need to use the -scale option with xmovie. When xmovie runs
it opens a visualization window and a control window. The control
options are straightforward to use.
Xmovie was mostly written by Mike Uttormark (U Wisconsin) while he
spent a summer at Sandia. It displays 2d projections of a 3d domain.
While simple in design, it is an amazingly fast program that can
render large numbers of atoms very quickly. It's a useful tool for
debugging LAMMPS input and output and making sure your simulation is
doing what you think it should. The animations on the Examples page
of the "LAMMPS WWW site"_lws were created with xmovie.
I've lost contact with Mike, so I hope he's comfortable with us
distributing his great tool!
diff --git a/doc/fix_langevin.html b/doc/fix_langevin.html
index b6f95ce7f..8d54104a7 100644
--- a/doc/fix_langevin.html
+++ b/doc/fix_langevin.html
@@ -1,207 +1,211 @@
<HTML>
<CENTER><A HREF = "http://lammps.sandia.gov">LAMMPS WWW Site</A> - <A HREF = "Manual.html">LAMMPS Documentation</A> - <A HREF = "Section_commands.html#comm">LAMMPS Commands</A>
</CENTER>
<HR>
<H3>fix langevin command
</H3>
<P><B>Syntax:</B>
</P>
<PRE>fix ID group-ID langevin Tstart Tstop damp seed keyword values ...
</PRE>
<UL><LI>ID, group-ID are documented in <A HREF = "fix.html">fix</A> command
<LI>langevin = style name of this fix command
<LI>Tstart,Tstop = desired temperature at start/end of run (temperature units)
<LI>damp = damping parameter (time units)
<LI>seed = random number seed to use for white noise (positive integer)
<LI>zero or more keyword/value pairs may be appended
<PRE>keyword = <I>scale</I> or <I>tally</I>
<I>scale</I> values = type ratio
type = atom type (1-N)
ratio = factor by which to scale the damping coefficient
<I>tally</I> values = <I>no</I> or <I>yes</I>
<I>no</I> = do not tally the energy added/subtracted to atoms
<I>yes</I> = do tally the energy added/subtracted to atoms
</PRE>
</UL>
<P><B>Examples:</B>
</P>
<PRE>fix 3 boundary langevin 1.0 1.0 1000.0 699483
fix 1 all langevin 1.0 1.1 100.0 48279 scale 3 1.5
</PRE>
<P><B>Description:</B>
</P>
<P>Apply a Langevin thermostat as described in <A HREF = "#Schneider">(Schneider)</A>
to a group of atoms which models an interaction with a background
implicit solvent. Used with <A HREF = "fix_nve.html">fix nve</A>, this command
performs Brownian dynamics (BD), since the total force on each atom
will have the form:
</P>
<PRE>F = Fc + Ff + Fr
Ff = - (m / damp) v
Fr is proportional to sqrt(Kb T m / (dt damp))
</PRE>
<P>Fc is the conservative force computed via the usual inter-particle
interactions (<A HREF = "pair_style.html">pair_style</A>,
<A HREF = "bond_style.html">bond_style</A>, etc).
</P>
-<P>The Ff and Fr terms are added by this fix.
+<P>The Ff and Fr terms are added by this fix on a per-particle basis.
+See the <A HREF = "pair_dpd.html">pair_style dpd/tstat</A> command for a
+thermostatting option that adds similar terms on a pairwise basis to
+pairs of interacting particles.
</P>
<P>Ff is a frictional drag or viscous damping term proportional to the
particle's velocity. The proportionality constant for each atom is
computed as m/damp, where m is the mass of the particle and damp is
the damping factor specified by the user.
</P>
<P>Fr is a force due to solvent atoms at a temperature T randomly bumping
into the particle. As derived from the fluctuation/dissipation
theorem, its magnitude as shown above is proportional to sqrt(Kb T m /
dt damp), where Kb is the Boltzmann constant, T is the desired
temperature, m is the mass of the particle, dt is the timestep size,
and damp is the damping factor. Random numbers are used to randomize
the direction and magnitude of this force as described in
<A HREF = "#Dunweg">(Dunweg)</A>, where a uniform random number is used (instead of
a Gaussian random number) for speed.
</P>
<P>Note that the thermostat effect of this fix is applied to only the
translational degrees of freedom for the particles, which is an
important consideration if extended spherical or aspherical particles
which have rotational degrees of freedom are being thermostatted with
this fix. The translational degrees of freedom can also have a bias
velocity removed from them before thermostatting takes place; see the
description below.
</P>
<P>IMPORTANT NOTE: Unlike the <A HREF = "fix_nh.html">fix nvt</A> command which
performs Nose/Hoover thermostatting AND time integration, this fix
does NOT perform time integration. It only modifies forces to effect
thermostatting. Thus you must use a separate time integration fix,
like <A HREF = "fix_nve.html">fix nve</A> to actually update the velocities and
positions of atoms using the modified forces. Likewise, this fix
should not normally be used on atoms that also have their temperature
controlled by another fix - e.g. by <A HREF = "fix_nh.html">fix nvt</A> or <A HREF = "fix_temp_rescale.html">fix
temp/rescale</A> commands.
</P>
<P>See <A HREF = "Section_howto.html#4_16">this howto section</A> of the manual for a
discussion of different ways to compute temperature and perform
thermostatting.
</P>
<P>The desired temperature at each timestep is a ramped value during the
run from <I>Tstart</I> to <I>Tstop</I>.
</P>
<P>Like other fixes that perform thermostatting, this fix can be used
with <A HREF = "compute.html">compute commands</A> that remove a "bias" from the
atom velocities. E.g. removing the center-of-mass velocity from a
group of atoms or removing the x-component of velocity from the
calculation. This is not done by default, but only if the
<A HREF = "fix_modify.html">fix_modify</A> command is used to assign a temperature
compute to this fix that includes such a bias term. See the doc pages
for individual <A HREF = "compute.html">compute commands</A> to determine which ones
include a bias. In this case, the thermostat works in the following
manner: bias is removed from each atom, thermostatting is performed on
the remaining thermal degrees of freedom, and the bias is added back
in.
</P>
<P>The <I>damp</I> parameter is specified in time units and determines how
rapidly the temperature is relaxed. For example, a value of 100.0
means to relax the temperature in a timespan of (roughly) 100 time
units (tau or fmsec or psec - see the <A HREF = "units.html">units</A> command).
The damp factor can be thought of as inversely related to the
viscosity of the solvent. I.e. a small relaxation time implies a
hi-viscosity solvent and vice versa. See the discussion about gamma
and viscosity in the documentation for the <A HREF = "fix_viscous.html">fix
viscous</A> command for more details.
</P>
<P>The random # <I>seed</I> must be a positive integer. A Marsaglia random
number generator is used. Each processor uses the input seed to
generate its own unique seed and its own stream of random numbers.
Thus the dynamics of the system will not be identical on two runs on
different numbers of processors.
</P>
<P>The keyword <I>scale</I> allows the damp factor to be scaled up or down by
the specified factor for atoms of that type. This can be useful when
different atom types have different sizes or masses. It can be used
multiple times to adjust damp for several atom types. Note that
specifying a ratio of 2 increases the relaxation time which is
equivalent to the solvent's viscosity acting on particles with 1/2 the
diameter. This is the opposite effect of scale factors used by the
<A HREF = "fix_viscous.html">fix viscous</A> command, since the damp factor in fix
<I>langevin</I> is inversely related to the gamma factor in fix <I>viscous</I>.
Also note that the damping factor in fix <I>langevin</I> includes the
particle mass in Ff, unlike fix <I>viscous</I>. Thus the mass and size of
different atom types should be accounted for in the choice of ratio
values.
</P>
<P>The keyword <I>tally</I> enables the calculation of the cummulative energy
added/subtracted to the atoms as they are thermostatted. Effectively
it is the energy exchanged between the infinite thermal reservoir and
the particles. As described below, this energy can then be printed
out or added to the potential energy of the system to monitor energy
conservation.
</P>
<P><B>Restart, fix_modify, output, run start/stop, minimize info:</B>
</P>
<P>No information about this fix is written to <A HREF = "restart.html">binary restart
files</A>. Because the state of the random number generator
is not saved in restart files, this means you cannot do "exact"
restarts with this fix, where the simulation continues on the same as
if no restart had taken place. However, in a statistical sense, a
restarted simulation should produce the same behavior.
</P>
<P>The <A HREF = "fix_modify.html">fix_modify</A> <I>temp</I> option is supported by this
fix. You can use it to assign a temperature <A HREF = "compute.html">compute</A>
you have defined to this fix which will be used in its thermostatting
procedure, as described above. For consistency, the group used by
this fix and by the compute should be the same.
</P>
<P>The <A HREF = "fix_modify.html">fix_modify</A> <I>energy</I> option is supported by this
fix to add the energy change induced by Langevin thermostatting to the
system's potential energy as part of <A HREF = "thermo_style.html">thermodynamic
output</A>. Note that use of this option requires
setting the <I>tally</I> keyword to <I>yes</I>.
</P>
<P>This fix computes a global scalar which can be accessed by various
<A HREF = "Section_howto.html#4_15">output commands</A>. The scalar is the
cummulative energy change due to this fix. The scalar value
calculated by this fix is "extensive". Note that calculation of this
quantity requires setting the <I>tally</I> keyword to <I>yes</I>.
</P>
<P>This fix can ramp its target temperature over multiple runs, using the
<I>start</I> and <I>stop</I> keywords of the <A HREF = "run.html">run</A> command. See the
<A HREF = "run.html">run</A> command for details of how to do this.
</P>
<P>This fix is not invoked during <A HREF = "minimize.html">energy minimization</A>.
</P>
<P><B>Restrictions:</B> none
</P>
<P><B>Related commands:</B>
</P>
<P><A HREF = "fix_nh.html">fix nvt</A>, <A HREF = "fix_temp_rescale.html">fix temp/rescale</A>, <A HREF = "fix_viscous.html">fix
-viscous</A>, <A HREF = "fix_nh.html">fix nvt</A>
+viscous</A>, <A HREF = "fix_nh.html">fix nvt</A>, <A HREF = "pair_dpd.html">pair_style
+dpd/tstat</A>
</P>
<P><B>Default:</B>
</P>
<P>The option defaults are scale = 1.0 for all types and tally = no.
</P>
<HR>
<A NAME = "Dunweg"></A>
<P><B>(Dunweg)</B> Dunweg and Paul, Int J of Modern Physics C, 2, 817-27 (1991).
</P>
<A NAME = "Schneider"></A>
<P><B>(Schneider)</B> Schneider and Stoll, Phys Rev B, 17, 1302 (1978).
</P>
</HTML>
diff --git a/doc/fix_langevin.txt b/doc/fix_langevin.txt
index 858df5329..f693f7fbc 100644
--- a/doc/fix_langevin.txt
+++ b/doc/fix_langevin.txt
@@ -1,193 +1,197 @@
"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Section_commands.html#comm)
:line
fix langevin command :h3
[Syntax:]
fix ID group-ID langevin Tstart Tstop damp seed keyword values ... :pre
ID, group-ID are documented in "fix"_fix.html command :ulb,l
langevin = style name of this fix command :l
Tstart,Tstop = desired temperature at start/end of run (temperature units) :l
damp = damping parameter (time units) :l
seed = random number seed to use for white noise (positive integer) :l
zero or more keyword/value pairs may be appended :l
keyword = {scale} or {tally}
{scale} values = type ratio
type = atom type (1-N)
ratio = factor by which to scale the damping coefficient
{tally} values = {no} or {yes}
{no} = do not tally the energy added/subtracted to atoms
{yes} = do tally the energy added/subtracted to atoms :pre
:ule
[Examples:]
fix 3 boundary langevin 1.0 1.0 1000.0 699483
fix 1 all langevin 1.0 1.1 100.0 48279 scale 3 1.5 :pre
[Description:]
Apply a Langevin thermostat as described in "(Schneider)"_#Schneider
to a group of atoms which models an interaction with a background
implicit solvent. Used with "fix nve"_fix_nve.html, this command
performs Brownian dynamics (BD), since the total force on each atom
will have the form:
F = Fc + Ff + Fr
Ff = - (m / damp) v
Fr is proportional to sqrt(Kb T m / (dt damp)) :pre
Fc is the conservative force computed via the usual inter-particle
interactions ("pair_style"_pair_style.html,
"bond_style"_bond_style.html, etc).
-The Ff and Fr terms are added by this fix.
+The Ff and Fr terms are added by this fix on a per-particle basis.
+See the "pair_style dpd/tstat"_pair_dpd.html command for a
+thermostatting option that adds similar terms on a pairwise basis to
+pairs of interacting particles.
Ff is a frictional drag or viscous damping term proportional to the
particle's velocity. The proportionality constant for each atom is
computed as m/damp, where m is the mass of the particle and damp is
the damping factor specified by the user.
Fr is a force due to solvent atoms at a temperature T randomly bumping
into the particle. As derived from the fluctuation/dissipation
theorem, its magnitude as shown above is proportional to sqrt(Kb T m /
dt damp), where Kb is the Boltzmann constant, T is the desired
temperature, m is the mass of the particle, dt is the timestep size,
and damp is the damping factor. Random numbers are used to randomize
the direction and magnitude of this force as described in
"(Dunweg)"_#Dunweg, where a uniform random number is used (instead of
a Gaussian random number) for speed.
Note that the thermostat effect of this fix is applied to only the
translational degrees of freedom for the particles, which is an
important consideration if extended spherical or aspherical particles
which have rotational degrees of freedom are being thermostatted with
this fix. The translational degrees of freedom can also have a bias
velocity removed from them before thermostatting takes place; see the
description below.
IMPORTANT NOTE: Unlike the "fix nvt"_fix_nh.html command which
performs Nose/Hoover thermostatting AND time integration, this fix
does NOT perform time integration. It only modifies forces to effect
thermostatting. Thus you must use a separate time integration fix,
like "fix nve"_fix_nve.html to actually update the velocities and
positions of atoms using the modified forces. Likewise, this fix
should not normally be used on atoms that also have their temperature
controlled by another fix - e.g. by "fix nvt"_fix_nh.html or "fix
temp/rescale"_fix_temp_rescale.html commands.
See "this howto section"_Section_howto.html#4_16 of the manual for a
discussion of different ways to compute temperature and perform
thermostatting.
The desired temperature at each timestep is a ramped value during the
run from {Tstart} to {Tstop}.
Like other fixes that perform thermostatting, this fix can be used
with "compute commands"_compute.html that remove a "bias" from the
atom velocities. E.g. removing the center-of-mass velocity from a
group of atoms or removing the x-component of velocity from the
calculation. This is not done by default, but only if the
"fix_modify"_fix_modify.html command is used to assign a temperature
compute to this fix that includes such a bias term. See the doc pages
for individual "compute commands"_compute.html to determine which ones
include a bias. In this case, the thermostat works in the following
manner: bias is removed from each atom, thermostatting is performed on
the remaining thermal degrees of freedom, and the bias is added back
in.
The {damp} parameter is specified in time units and determines how
rapidly the temperature is relaxed. For example, a value of 100.0
means to relax the temperature in a timespan of (roughly) 100 time
units (tau or fmsec or psec - see the "units"_units.html command).
The damp factor can be thought of as inversely related to the
viscosity of the solvent. I.e. a small relaxation time implies a
hi-viscosity solvent and vice versa. See the discussion about gamma
and viscosity in the documentation for the "fix
viscous"_fix_viscous.html command for more details.
The random # {seed} must be a positive integer. A Marsaglia random
number generator is used. Each processor uses the input seed to
generate its own unique seed and its own stream of random numbers.
Thus the dynamics of the system will not be identical on two runs on
different numbers of processors.
The keyword {scale} allows the damp factor to be scaled up or down by
the specified factor for atoms of that type. This can be useful when
different atom types have different sizes or masses. It can be used
multiple times to adjust damp for several atom types. Note that
specifying a ratio of 2 increases the relaxation time which is
equivalent to the solvent's viscosity acting on particles with 1/2 the
diameter. This is the opposite effect of scale factors used by the
"fix viscous"_fix_viscous.html command, since the damp factor in fix
{langevin} is inversely related to the gamma factor in fix {viscous}.
Also note that the damping factor in fix {langevin} includes the
particle mass in Ff, unlike fix {viscous}. Thus the mass and size of
different atom types should be accounted for in the choice of ratio
values.
The keyword {tally} enables the calculation of the cummulative energy
added/subtracted to the atoms as they are thermostatted. Effectively
it is the energy exchanged between the infinite thermal reservoir and
the particles. As described below, this energy can then be printed
out or added to the potential energy of the system to monitor energy
conservation.
[Restart, fix_modify, output, run start/stop, minimize info:]
No information about this fix is written to "binary restart
files"_restart.html. Because the state of the random number generator
is not saved in restart files, this means you cannot do "exact"
restarts with this fix, where the simulation continues on the same as
if no restart had taken place. However, in a statistical sense, a
restarted simulation should produce the same behavior.
The "fix_modify"_fix_modify.html {temp} option is supported by this
fix. You can use it to assign a temperature "compute"_compute.html
you have defined to this fix which will be used in its thermostatting
procedure, as described above. For consistency, the group used by
this fix and by the compute should be the same.
The "fix_modify"_fix_modify.html {energy} option is supported by this
fix to add the energy change induced by Langevin thermostatting to the
system's potential energy as part of "thermodynamic
output"_thermo_style.html. Note that use of this option requires
setting the {tally} keyword to {yes}.
This fix computes a global scalar which can be accessed by various
"output commands"_Section_howto.html#4_15. The scalar is the
cummulative energy change due to this fix. The scalar value
calculated by this fix is "extensive". Note that calculation of this
quantity requires setting the {tally} keyword to {yes}.
This fix can ramp its target temperature over multiple runs, using the
{start} and {stop} keywords of the "run"_run.html command. See the
"run"_run.html command for details of how to do this.
This fix is not invoked during "energy minimization"_minimize.html.
[Restrictions:] none
[Related commands:]
"fix nvt"_fix_nh.html, "fix temp/rescale"_fix_temp_rescale.html, "fix
-viscous"_fix_viscous.html, "fix nvt"_fix_nh.html
+viscous"_fix_viscous.html, "fix nvt"_fix_nh.html, "pair_style
+dpd/tstat"_pair_dpd.html
[Default:]
The option defaults are scale = 1.0 for all types and tally = no.
:line
:link(Dunweg)
[(Dunweg)] Dunweg and Paul, Int J of Modern Physics C, 2, 817-27 (1991).
:link(Schneider)
[(Schneider)] Schneider and Stoll, Phys Rev B, 17, 1302 (1978).
diff --git a/doc/pair_coeff.html b/doc/pair_coeff.html
index d00d2af59..dd5042e89 100644
--- a/doc/pair_coeff.html
+++ b/doc/pair_coeff.html
@@ -1,168 +1,169 @@
<HTML>
<CENTER><A HREF = "http://lammps.sandia.gov">LAMMPS WWW Site</A> - <A HREF = "Manual.html">LAMMPS Documentation</A> - <A HREF = "Section_commands.html#comm">LAMMPS Commands</A>
</CENTER>
<HR>
<H3>pair_coeff command
</H3>
<P><B>Syntax:</B>
</P>
<PRE>pair_coeff I J args
</PRE>
<UL><LI>I,J = atom types (see asterisk form below)
<LI>args = coefficients for one or more pairs of atom types
</UL>
<P><B>Examples:</B>
</P>
<PRE>pair_coeff 1 2 1.0 1.0 2.5
pair_coeff 2 * 1.0 1.0
pair_coeff 3* 1*2 1.0 1.0 2.5
pair_coeff * * 1.0 1.0
pair_coeff * * nialhjea 1 1 2
pair_coeff * 3 morse.table ENTRY1
pair_coeff 1 2 lj/cut 1.0 1.0 2.5 (for pair_style hybrid)
</PRE>
<P><B>Description:</B>
</P>
<P>Specify the pairwise force field coefficients for one or more pairs of
atom types. The number and meaning of the coefficients depends on the
pair style. Pair coefficients can also be set in the data file read
by the <A HREF = "read_data.html">read_data</A> command or in a restart file.
</P>
<P>I and J can be specified in one of two ways. Explicit numeric values
can be used for each, as in the 1st example above. I <= J is
required. LAMMPS sets the coefficients for the symmetric J,I
interaction to the same values.
</P>
<P>A wild-card asterisk can be used in place of or in conjunction with the
I,J arguments to set the coefficients for multiple pairs of atom
types. This takes the form "*" or "*n" or "n*" or "m*n". If N = the
number of atom types, then an asterisk with no numeric values means all
types from 1 to N. A leading asterisk means all types from 1 to n
(inclusive). A trailing asterisk means all types from n to N
(inclusive). A middle asterisk means all types from m to n
(inclusive). Note that only type pairs with I <= J are considered; if
asterisks imply type pairs where J < I, they are ignored.
</P>
<P>Note that a pair_coeff command can override a previous setting for the
same I,J pair. For example, these commands set the coeffs for all I,J
pairs, then overwrite the coeffs for just the I,J = 2,3 pair:
</P>
<PRE>pair_coeff * * 1.0 1.0 2.5
pair_coeff 2 3 2.0 1.0 1.12
</PRE>
<P>A line in a data file that specifies pair coefficients uses the exact
same format as the arguments of the pair_coeff command in an input
script, with the exception of the I,J type arguments. In each line of
the "Pair Coeffs" section of a data file, only a single type I is
specified, which sets the coefficients for type I interacting with
type I. This is because the section has exactly N lines, where N =
the number of atom types. For this reason, the wild-card asterisk
should also not be used as part of the I argument. Thus in a data
file, the line corresponding to the 1st example above would be listed
as
</P>
<PRE>2 1.0 1.0 2.5
</PRE>
<P>For many potentials, if coefficients for type pairs with I != J are
not set explicitly by a pair_coeff command, the values are inferred
from the I,I and J,J settings by mixing rules; see the
<A HREF = "pair_modify.html">pair_modify</A> command for a discussion. Details on
this option as it pertains to individual potentials are described on
the doc page for the potential.
</P>
<HR>
<P>Here is an alphabetic list of pair styles defined in LAMMPS. Click on
the style to display the formula it computes, arguments specified in
the pair_style command, and coefficients specified by the associated
<A HREF = "pair_coeff.html">pair_coeff</A> command:
</P>
<UL><LI><A HREF = "pair_hybrid.html">pair_style hybrid</A> - multiple styles of pairwise interactions
<LI><A HREF = "pair_hybrid.html">pair_style hybrid/overlay</A> - multiple styles of superposed pairwise interactions
</UL>
<UL><LI><A HREF = "pair_airebo.html">pair_style airebo</A> - AI-REBO potential
<LI><A HREF = "pair_born.html">pair_style born/coul/long</A> - Born-Mayer-Huggins with long-range Coulomb
<LI><A HREF = "pair_buck.html">pair_style buck</A> - Buckingham potential
<LI><A HREF = "pair_buck.html">pair_style buck/coul/cut</A> - Buckingham with cutoff Coulomb
<LI><A HREF = "pair_buck.html">pair_style buck/coul/long</A> - Buckingham with long-range Coulomb
<LI><A HREF = "pair_colloid.html">pair_style colloid</A> - integrated colloidal potential
<LI><A HREF = "pair_coul.html">pair_style coul/cut</A> - cutoff Coulombic potential
<LI><A HREF = "pair_coul.html">pair_style coul/debye</A> - cutoff Coulombic potential with Debye screening
<LI><A HREF = "pair_coul.html">pair_style coul/long</A> - long-range Coulombic potential
<LI><A HREF = "pair_dipole.html">pair_style dipole/cut</A> - point dipoles with cutoff
<LI><A HREF = "pair_dpd.html">pair_style dpd</A> - dissipative particle dynamics (DPD)
+<LI><A HREF = "pair_dpd.html">pair_style dpd/tstat</A> - DPD thermostatting
<LI><A HREF = "pair_dsmc.html">pair_style dsmc</A> - Direct Simulation Monte Carlo (DSMC)
<LI><A HREF = "pair_eam.html">pair_style eam</A> - embedded atom method (EAM)
<LI><A HREF = "pair_eam.html">pair_style eam/opt</A> - optimized version of EAM
<LI><A HREF = "pair_eam.html">pair_style eam/alloy</A> - alloy EAM
<LI><A HREF = "pair_eam.html">pair_style eam/alloy/opt</A> - optimized version of alloy EAM
<LI><A HREF = "pair_eam.html">pair_style eam/fs</A> - Finnis-Sinclair EAM
<LI><A HREF = "pair_eam.html">pair_style eam/fs/opt</A> - optimized version of Finnis-Sinclair EAM
<LI><A HREF = "pair_gayberne.html">pair_style gayberne</A> - Gay-Berne ellipsoidal potential
<LI><A HREF = "pair_gayberne.html">pair_style gayberne/gpu</A> - GPU-enabled Gay-Berne ellipsoidal potential
<LI><A HREF = "pair_gran.html">pair_style gran/hertz/history</A> - granular potential with Hertzian interactions
<LI><A HREF = "pair_gran.html">pair_style gran/hooke</A> - granular potential with history effects
<LI><A HREF = "pair_gran.html">pair_style gran/hooke/history</A> - granular potential without history effects
<LI><A HREF = "pair_charmm.html">pair_style lj/charmm/coul/charmm</A> - CHARMM potential with cutoff Coulomb
<LI><A HREF = "pair_charmm.html">pair_style lj/charmm/coul/charmm/implicit</A> - CHARMM for implicit solvent
<LI><A HREF = "pair_charmm.html">pair_style lj/charmm/coul/long</A> - CHARMM with long-range Coulomb
<LI><A HREF = "pair_charmm.html">pair_style lj/charmm/coul/long/opt</A> - optimized version of CHARMM with long-range Coulomb
<LI><A HREF = "pair_class2.html">pair_style lj/class2</A> - COMPASS (class 2) force field with no Coulomb
<LI><A HREF = "pair_class2.html">pair_style lj/class2/coul/cut</A> - COMPASS with cutoff Coulomb
<LI><A HREF = "pair_class2.html">pair_style lj/class2/coul/long</A> - COMPASS with long-range Coulomb
<LI><A HREF = "pair_lj.html">pair_style lj/cut</A> - cutoff Lennard-Jones potential with no Coulomb
<LI><A HREF = "pair_lj.html">pair_style lj/cut/gpu</A> - GPU-enabled version of cutoff LJ
<LI><A HREF = "pair_lj.html">pair_style lj/cut/opt</A> - optimized version of cutoff LJ
<LI><A HREF = "pair_lj.html">pair_style lj/cut/coul/cut</A> - LJ with cutoff Coulomb
<LI><A HREF = "pair_lj.html">pair_style lj/cut/coul/debye</A> - LJ with Debye screening added to Coulomb
<LI><A HREF = "pair_lj.html">pair_style lj/cut/coul/long</A> - LJ with long-range Coulomb
<LI><A HREF = "pair_lj.html">pair_style lj/cut/coul/long/tip4p</A> - LJ with long-range Coulomb for TIP4P water
<LI><A HREF = "pair_lj_expand.html">pair_style lj/expand</A> - Lennard-Jones for variable size particles
<LI><A HREF = "pair_gromacs.html">pair_style lj/gromacs</A> - GROMACS-style Lennard-Jones potential
<LI><A HREF = "pair_gromacs.html">pair_style lj/gromacs/coul/gromacs</A> - GROMACS-style LJ and Coulombic potential
<LI><A HREF = "pair_lj_smooth.html">pair_style lj/smooth</A> - smoothed Lennard-Jones potential
<LI><A HREF = "pair_lj96_cut.html">pair_style lj96/cut</A> - Lennard-Jones 9/6 potential
<LI><A HREF = "pair_lubricate.html">pair_style lubricate</A> - hydrodynamic lubrication forces
<LI><A HREF = "pair_meam.html">pair_style meam</A> - modified embedded atom method (MEAM)
<LI><A HREF = "pair_morse.html">pair_style morse</A> - Morse potential
<LI><A HREF = "pair_morse.html">pair_style morse/opt</A> - optimized version of Morse potential
<LI><A HREF = "pair_peri_pmb.html">pair_style peri/pmb</A> - peridynamic PMB potential
<LI><A HREF = "pair_reax.html">pair_style reax</A> - ReaxFF potential
<LI><A HREF = "pair_resquared.html">pair_style resquared</A> - Everaers RE-Squared ellipsoidal potential
<LI><A HREF = "pair_soft.html">pair_style soft</A> - Soft (cosine) potential
<LI><A HREF = "pair_sw.html">pair_style sw</A> - Stillinger-Weber 3-body potential
<LI><A HREF = "pair_table.html">pair_style table</A> - tabulated pair potential
<LI><A HREF = "pair_tersoff.html">pair_style tersoff</A> - Tersoff 3-body potential
<LI><A HREF = "pair_tersoff_zbl.html">pair_style tersoff/zbl</A> - Tersoff/ZBL 3-body potential
<LI><A HREF = "pair_yukawa.html">pair_style yukawa</A> - Yukawa potential
<LI><A HREF = "pair_yukawa_colloid.html">pair_style yukawa/colloid</A> - screened Yukawa potential for finite-size particles
</UL>
<P>There are also additional pair styles submitted by users which are
included in the LAMMPS distribution. The list of these with links to
the individual styles are given in the pair section of <A HREF = "Section_commands.html#3_5">this
page</A>.
</P>
<HR>
<P><B>Restrictions:</B>
</P>
<P>This command must come after the simulation box is defined by a
<A HREF = "read_data.html">read_data</A>, <A HREF = "read_restart.html">read_restart</A>, or
<A HREF = "create_box.html">create_box</A> command.
</P>
<P><B>Related commands:</B>
</P>
<P><A HREF = "pair_style.html">pair_style</A>, <A HREF = "pair_modify.html">pair_modify</A>,
<A HREF = "read_data.html">read_data</A>, <A HREF = "read_restart.html">read_restart</A>,
<A HREF = "pair_write.html">pair_write</A>
</P>
<P><B>Default:</B> none
</P>
</HTML>
diff --git a/doc/pair_coeff.txt b/doc/pair_coeff.txt
index c8cb33d48..650dee6ed 100644
--- a/doc/pair_coeff.txt
+++ b/doc/pair_coeff.txt
@@ -1,163 +1,164 @@
"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Section_commands.html#comm)
:line
pair_coeff command :h3
[Syntax:]
pair_coeff I J args :pre
I,J = atom types (see asterisk form below)
args = coefficients for one or more pairs of atom types :ul
[Examples:]
pair_coeff 1 2 1.0 1.0 2.5
pair_coeff 2 * 1.0 1.0
pair_coeff 3* 1*2 1.0 1.0 2.5
pair_coeff * * 1.0 1.0
pair_coeff * * nialhjea 1 1 2
pair_coeff * 3 morse.table ENTRY1
pair_coeff 1 2 lj/cut 1.0 1.0 2.5 (for pair_style hybrid) :pre
[Description:]
Specify the pairwise force field coefficients for one or more pairs of
atom types. The number and meaning of the coefficients depends on the
pair style. Pair coefficients can also be set in the data file read
by the "read_data"_read_data.html command or in a restart file.
I and J can be specified in one of two ways. Explicit numeric values
can be used for each, as in the 1st example above. I <= J is
required. LAMMPS sets the coefficients for the symmetric J,I
interaction to the same values.
A wild-card asterisk can be used in place of or in conjunction with the
I,J arguments to set the coefficients for multiple pairs of atom
types. This takes the form "*" or "*n" or "n*" or "m*n". If N = the
number of atom types, then an asterisk with no numeric values means all
types from 1 to N. A leading asterisk means all types from 1 to n
(inclusive). A trailing asterisk means all types from n to N
(inclusive). A middle asterisk means all types from m to n
(inclusive). Note that only type pairs with I <= J are considered; if
asterisks imply type pairs where J < I, they are ignored.
Note that a pair_coeff command can override a previous setting for the
same I,J pair. For example, these commands set the coeffs for all I,J
pairs, then overwrite the coeffs for just the I,J = 2,3 pair:
pair_coeff * * 1.0 1.0 2.5
pair_coeff 2 3 2.0 1.0 1.12 :pre
A line in a data file that specifies pair coefficients uses the exact
same format as the arguments of the pair_coeff command in an input
script, with the exception of the I,J type arguments. In each line of
the "Pair Coeffs" section of a data file, only a single type I is
specified, which sets the coefficients for type I interacting with
type I. This is because the section has exactly N lines, where N =
the number of atom types. For this reason, the wild-card asterisk
should also not be used as part of the I argument. Thus in a data
file, the line corresponding to the 1st example above would be listed
as
2 1.0 1.0 2.5 :pre
For many potentials, if coefficients for type pairs with I != J are
not set explicitly by a pair_coeff command, the values are inferred
from the I,I and J,J settings by mixing rules; see the
"pair_modify"_pair_modify.html command for a discussion. Details on
this option as it pertains to individual potentials are described on
the doc page for the potential.
:line
Here is an alphabetic list of pair styles defined in LAMMPS. Click on
the style to display the formula it computes, arguments specified in
the pair_style command, and coefficients specified by the associated
"pair_coeff"_pair_coeff.html command:
"pair_style hybrid"_pair_hybrid.html - multiple styles of pairwise interactions
"pair_style hybrid/overlay"_pair_hybrid.html - multiple styles of superposed pairwise interactions :ul
"pair_style airebo"_pair_airebo.html - AI-REBO potential
"pair_style born/coul/long"_pair_born.html - Born-Mayer-Huggins with long-range Coulomb
"pair_style buck"_pair_buck.html - Buckingham potential
"pair_style buck/coul/cut"_pair_buck.html - Buckingham with cutoff Coulomb
"pair_style buck/coul/long"_pair_buck.html - Buckingham with long-range Coulomb
"pair_style colloid"_pair_colloid.html - integrated colloidal potential
"pair_style coul/cut"_pair_coul.html - cutoff Coulombic potential
"pair_style coul/debye"_pair_coul.html - cutoff Coulombic potential with Debye screening
"pair_style coul/long"_pair_coul.html - long-range Coulombic potential
"pair_style dipole/cut"_pair_dipole.html - point dipoles with cutoff
"pair_style dpd"_pair_dpd.html - dissipative particle dynamics (DPD)
+"pair_style dpd/tstat"_pair_dpd.html - DPD thermostatting
"pair_style dsmc"_pair_dsmc.html - Direct Simulation Monte Carlo (DSMC)
"pair_style eam"_pair_eam.html - embedded atom method (EAM)
"pair_style eam/opt"_pair_eam.html - optimized version of EAM
"pair_style eam/alloy"_pair_eam.html - alloy EAM
"pair_style eam/alloy/opt"_pair_eam.html - optimized version of alloy EAM
"pair_style eam/fs"_pair_eam.html - Finnis-Sinclair EAM
"pair_style eam/fs/opt"_pair_eam.html - optimized version of Finnis-Sinclair EAM
"pair_style gayberne"_pair_gayberne.html - Gay-Berne ellipsoidal potential
"pair_style gayberne/gpu"_pair_gayberne.html - GPU-enabled Gay-Berne ellipsoidal potential
"pair_style gran/hertz/history"_pair_gran.html - granular potential with Hertzian interactions
"pair_style gran/hooke"_pair_gran.html - granular potential with history effects
"pair_style gran/hooke/history"_pair_gran.html - granular potential without history effects
"pair_style lj/charmm/coul/charmm"_pair_charmm.html - CHARMM potential with cutoff Coulomb
"pair_style lj/charmm/coul/charmm/implicit"_pair_charmm.html - CHARMM for implicit solvent
"pair_style lj/charmm/coul/long"_pair_charmm.html - CHARMM with long-range Coulomb
"pair_style lj/charmm/coul/long/opt"_pair_charmm.html - optimized version of CHARMM with long-range Coulomb
"pair_style lj/class2"_pair_class2.html - COMPASS (class 2) force field with no Coulomb
"pair_style lj/class2/coul/cut"_pair_class2.html - COMPASS with cutoff Coulomb
"pair_style lj/class2/coul/long"_pair_class2.html - COMPASS with long-range Coulomb
"pair_style lj/cut"_pair_lj.html - cutoff Lennard-Jones potential with no Coulomb
"pair_style lj/cut/gpu"_pair_lj.html - GPU-enabled version of cutoff LJ
"pair_style lj/cut/opt"_pair_lj.html - optimized version of cutoff LJ
"pair_style lj/cut/coul/cut"_pair_lj.html - LJ with cutoff Coulomb
"pair_style lj/cut/coul/debye"_pair_lj.html - LJ with Debye screening added to Coulomb
"pair_style lj/cut/coul/long"_pair_lj.html - LJ with long-range Coulomb
"pair_style lj/cut/coul/long/tip4p"_pair_lj.html - LJ with long-range Coulomb for TIP4P water
"pair_style lj/expand"_pair_lj_expand.html - Lennard-Jones for variable size particles
"pair_style lj/gromacs"_pair_gromacs.html - GROMACS-style Lennard-Jones potential
"pair_style lj/gromacs/coul/gromacs"_pair_gromacs.html - GROMACS-style LJ and Coulombic potential
"pair_style lj/smooth"_pair_lj_smooth.html - smoothed Lennard-Jones potential
"pair_style lj96/cut"_pair_lj96_cut.html - Lennard-Jones 9/6 potential
"pair_style lubricate"_pair_lubricate.html - hydrodynamic lubrication forces
"pair_style meam"_pair_meam.html - modified embedded atom method (MEAM)
"pair_style morse"_pair_morse.html - Morse potential
"pair_style morse/opt"_pair_morse.html - optimized version of Morse potential
"pair_style peri/pmb"_pair_peri_pmb.html - peridynamic PMB potential
"pair_style reax"_pair_reax.html - ReaxFF potential
"pair_style resquared"_pair_resquared.html - Everaers RE-Squared ellipsoidal potential
"pair_style soft"_pair_soft.html - Soft (cosine) potential
"pair_style sw"_pair_sw.html - Stillinger-Weber 3-body potential
"pair_style table"_pair_table.html - tabulated pair potential
"pair_style tersoff"_pair_tersoff.html - Tersoff 3-body potential
"pair_style tersoff/zbl"_pair_tersoff_zbl.html - Tersoff/ZBL 3-body potential
"pair_style yukawa"_pair_yukawa.html - Yukawa potential
"pair_style yukawa/colloid"_pair_yukawa_colloid.html - screened Yukawa potential for finite-size particles :ul
There are also additional pair styles submitted by users which are
included in the LAMMPS distribution. The list of these with links to
the individual styles are given in the pair section of "this
page"_Section_commands.html#3_5.
:line
[Restrictions:]
This command must come after the simulation box is defined by a
"read_data"_read_data.html, "read_restart"_read_restart.html, or
"create_box"_create_box.html command.
[Related commands:]
"pair_style"_pair_style.html, "pair_modify"_pair_modify.html,
"read_data"_read_data.html, "read_restart"_read_restart.html,
"pair_write"_pair_write.html
[Default:] none
diff --git a/doc/pair_dpd.html b/doc/pair_dpd.html
index 136a47fc9..ffed14396 100644
--- a/doc/pair_dpd.html
+++ b/doc/pair_dpd.html
@@ -1,122 +1,159 @@
<HTML>
<CENTER><A HREF = "http://lammps.sandia.gov">LAMMPS WWW Site</A> - <A HREF = "Manual.html">LAMMPS Documentation</A> - <A HREF = "Section_commands.html#comm">LAMMPS Commands</A>
</CENTER>
<HR>
<H3>pair_style dpd command
</H3>
+<H3>pair_style dpd/tstat command
+</H3>
<P><B>Syntax:</B>
</P>
-<PRE>pair_style dpd T cutoff seed
+<PRE>pair_style dpd T cutoff seed
+pair_style dpd/tstat Tstart Tstop cutoff seed
</PRE>
<UL><LI>T = temperature (temperature units)
+<LI>Tstart,Tstop = desired temperature at start/end of run (temperature units)
<LI>cutoff = global cutoff for DPD interactions (distance units)
<LI>seed = random # seed (positive integer)
</UL>
<P><B>Examples:</B>
</P>
<PRE>pair_style dpd 1.0 2.5 34387
pair_coeff * * 3.0 1.0
pair_coeff 1 1 3.0 1.0 1.0
</PRE>
+<PRE>pair_style dpd/tstat 1.0 1.0 2.5 34387
+pair_coeff * * 1.0
+pair_coeff 1 1 1.0 1.0
+</PRE>
<P><B>Description:</B>
</P>
<P>Style <I>dpd</I> computes a force field for dissipative particle dynamics
-(DPD) following the exposition in <A HREF = "#Groot">(Groot)</A>. The force
-on atom I due to atom J is given as a sum of 3 terms
+(DPD) following the exposition in <A HREF = "#Groot">(Groot)</A>.
+</P>
+<P>Style <I>dpd/tstat</I> invokes a DPD thermostat on pairwise interactions,
+which is equivalent to the non-conservative portion of the DPD force
+field. This thermostat can be used in conjunction with any <A HREF = "doc/pair_style.html">pair
+style</A>, and in leiu of per-particle thermostats
+like <A HREF = "fix_langevin.html">fix langevin</A> or ensemble thermostats like
+Nose Hoover as implemented by <A HREF = "fix_nvt.html">fix nvt</A>. To use
+<I>dpd/stat</I> with another pair style, use the <A HREF = "pair_hybrid.html">pair_style
+hybrid/overlay</A> command to compute both the desired
+pair interaction and the thermostat for each pair of particles.
+</P>
+<P>For style <I>dpd</I>, the force on atom I due to atom J is given as a sum
+of 3 terms
</P>
<CENTER><IMG SRC = "Eqs/pair_dpd.jpg">
</CENTER>
<P>where Fc is a conservative force, Fd is a dissipative force, and Fr is
a random force. Rij is a unit vector in the direction Ri - Rj, Vij is
the vector difference in velocities of the two atoms = Vi - Vj, alpha
is a Gaussian random number with zero mean and unit variance, dt is
the timestep size, and w(r) is a weighting factor that varies between
0 and 1. Rc is the cutoff. Sigma is set equal to sqrt(2 Kb T gamma),
where Kb is the Boltzmann constant and T is the temperature parameter
in the pair_style command.
</P>
-<P>The pairwise energy associated with this potential is only due to the
-conservative force term Fc.
+<P>For style <I>dpd/tstat</I>, the force on atom I due to atom J is the same
+as the above equation, except that the conservative Fc term is
+dropped. Also, during the run, T is set each timestep to a ramped
+value from Tstart to Tstop.
</P>
-<P>The following coefficients must be defined for each pair of atoms
-types via the <A HREF = "pair_coeff.html">pair_coeff</A> command as in the examples
-above, or in the data file or restart files read by the
+<P>For style <I>dpd</I>, the pairwise energy associated with style <I>dpd</I> is
+only due to the conservative force term Fc. The pairwise virial is
+calculated using all 3 terms. For style <I>dpd/tstat</I> there is no
+pairwise energy or virial.
+</P>
+<P>For style <I>dpd</I>, the following coefficients must be defined for each
+pair of atoms types via the <A HREF = "pair_coeff.html">pair_coeff</A> command as in
+the examples above, or in the data file or restart files read by the
<A HREF = "read_data.html">read_data</A> or <A HREF = "read_restart.html">read_restart</A>
commands:
</P>
<UL><LI>A (force units)
<LI>gamma (force/velocity units)
<LI>cutoff (distance units)
</UL>
<P>The last coefficient is optional. If not specified, the global DPD
cutoff is used. Note that sigma is set equal to sqrt(2 T gamma),
where T is the temperature set by the <A HREF = "pair_style.html">pair_style</A>
command so it does not need to be specified.
</P>
+<P>For style <I>dpd/tstat</I>, the coefficiencts defined for each pair of
+atoms types via the <A HREF = "pair_coeff.html">pair_coeff</A> command is the same,
+except that A is not included.
+</P>
<HR>
<P><B>Mixing, shift, table, tail correction, restart, rRESPA info</B>:
</P>
-<P>This pair style does not support mixing. Thus, coefficients for all
+<P>These pair styles do not support mixing. Thus, coefficients for all
I,J pairs must be specified explicitly.
</P>
-<P>This pair style does not support the <A HREF = "pair_modify.html">pair_modify</A>
+<P>These pair styles do not support the <A HREF = "pair_modify.html">pair_modify</A>
shift option for the energy of the pair interaction.
</P>
<P>The <A HREF = "pair_modify.html">pair_modify</A> table option is not relevant
-for this pair style.
+for these pair styles.
</P>
-<P>This pair style does not support the <A HREF = "pair_modify.html">pair_modify</A>
+<P>These pair style do not support the <A HREF = "pair_modify.html">pair_modify</A>
tail option for adding long-range tail corrections to energy and
pressure.
</P>
-<P>This pair style writes its information to <A HREF = "restart.html">binary restart
+<P>These pair styles writes their information to <A HREF = "restart.html">binary restart
files</A>, so pair_style and pair_coeff commands do not need
to be specified in an input script that reads a restart file. Note
that the user-specified random number seed is stored in the restart
file, so when a simulation is restarted, each processor will
re-initialize its random number generator the same way it did
initially. This means the random forces will be random, but will not
be the same as they would have been if the original simulation had
continued past the restart time.
</P>
-<P>This pair style can only be used via the <I>pair</I> keyword of the
-<A HREF = "run_style.html">run_style respa</A> command. It does not support the
+<P>These pair styles can only be used via the <I>pair</I> keyword of the
+<A HREF = "run_style.html">run_style respa</A> command. They do not support the
<I>inner</I>, <I>middle</I>, <I>outer</I> keywords.
</P>
+<P>The <I>dpd/tstat</I> style can ramp its target temperature over multiple
+runs, using the <I>start</I> and <I>stop</I> keywords of the <A HREF = "run.html">run</A>
+command. See the <A HREF = "run.html">run</A> command for details of how to do
+this.
+</P>
<HR>
<P><B>Restrictions:</B>
</P>
<P>The default frequency for rebuilding neighbor lists is every 10 steps
(see the <A HREF = "neigh_modify.html">neigh_modify</A> command). This may be too
-infrequent for DPD simulations since particles move rapidly and can
-overlap by large amounts. If this setting yields a non-zero number of
-"dangerous" reneighborings (printed at the end of a simulation), you
-should experiment with forcing reneighboring more often and see if
-system energies/trajectories change.
+infrequent for style <I>dpd</I> simulations since particles move rapidly
+and can overlap by large amounts. If this setting yields a non-zero
+number of "dangerous" reneighborings (printed at the end of a
+simulation), you should experiment with forcing reneighboring more
+often and see if system energies/trajectories change.
</P>
-<P>This pair style requires you to use the <A HREF = "communicate.html">communicate vel
+<P>These pair styles requires you to use the <A HREF = "communicate.html">communicate vel
yes</A> option so that velocites are stored by ghost
atoms.
</P>
<P><B>Related commands:</B>
</P>
-<P><A HREF = "pair_coeff.html">pair_coeff</A>
+<P><A HREF = "pair_coeff.html">pair_coeff</A>, <A HREF = "fix_nvt.html">fix nvt</A>, <A HREF = "fix_langevin.html">fix
+langevin</A>
</P>
<P><B>Default:</B> none
</P>
<HR>
<A NAME = "Groot"></A>
<P><B>(Groot)</B> Groot and Warren, J Chem Phys, 107, 4423-35 (1997).
</P>
</HTML>
diff --git a/doc/pair_dpd.txt b/doc/pair_dpd.txt
index 292e82b49..e89251115 100644
--- a/doc/pair_dpd.txt
+++ b/doc/pair_dpd.txt
@@ -1,116 +1,152 @@
"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Section_commands.html#comm)
:line
pair_style dpd command :h3
+pair_style dpd/tstat command :h3
[Syntax:]
-pair_style dpd T cutoff seed :pre
+pair_style dpd T cutoff seed
+pair_style dpd/tstat Tstart Tstop cutoff seed :pre
T = temperature (temperature units)
+Tstart,Tstop = desired temperature at start/end of run (temperature units)
cutoff = global cutoff for DPD interactions (distance units)
seed = random # seed (positive integer) :ul
[Examples:]
pair_style dpd 1.0 2.5 34387
pair_coeff * * 3.0 1.0
pair_coeff 1 1 3.0 1.0 1.0 :pre
+pair_style dpd/tstat 1.0 1.0 2.5 34387
+pair_coeff * * 1.0
+pair_coeff 1 1 1.0 1.0 :pre
+
[Description:]
Style {dpd} computes a force field for dissipative particle dynamics
-(DPD) following the exposition in "(Groot)"_#Groot. The force
-on atom I due to atom J is given as a sum of 3 terms
+(DPD) following the exposition in "(Groot)"_#Groot.
+
+Style {dpd/tstat} invokes a DPD thermostat on pairwise interactions,
+which is equivalent to the non-conservative portion of the DPD force
+field. This thermostat can be used in conjunction with any "pair
+style"_doc/pair_style.html, and in leiu of per-particle thermostats
+like "fix langevin"_fix_langevin.html or ensemble thermostats like
+Nose Hoover as implemented by "fix nvt"_fix_nvt.html. To use
+{dpd/stat} with another pair style, use the "pair_style
+hybrid/overlay"_pair_hybrid.html command to compute both the desired
+pair interaction and the thermostat for each pair of particles.
+
+For style {dpd}, the force on atom I due to atom J is given as a sum
+of 3 terms
:c,image(Eqs/pair_dpd.jpg)
where Fc is a conservative force, Fd is a dissipative force, and Fr is
a random force. Rij is a unit vector in the direction Ri - Rj, Vij is
the vector difference in velocities of the two atoms = Vi - Vj, alpha
is a Gaussian random number with zero mean and unit variance, dt is
the timestep size, and w(r) is a weighting factor that varies between
0 and 1. Rc is the cutoff. Sigma is set equal to sqrt(2 Kb T gamma),
where Kb is the Boltzmann constant and T is the temperature parameter
in the pair_style command.
-The pairwise energy associated with this potential is only due to the
-conservative force term Fc.
+For style {dpd/tstat}, the force on atom I due to atom J is the same
+as the above equation, except that the conservative Fc term is
+dropped. Also, during the run, T is set each timestep to a ramped
+value from Tstart to Tstop.
-The following coefficients must be defined for each pair of atoms
-types via the "pair_coeff"_pair_coeff.html command as in the examples
-above, or in the data file or restart files read by the
+For style {dpd}, the pairwise energy associated with style {dpd} is
+only due to the conservative force term Fc. The pairwise virial is
+calculated using all 3 terms. For style {dpd/tstat} there is no
+pairwise energy or virial.
+
+For style {dpd}, the following coefficients must be defined for each
+pair of atoms types via the "pair_coeff"_pair_coeff.html command as in
+the examples above, or in the data file or restart files read by the
"read_data"_read_data.html or "read_restart"_read_restart.html
commands:
A (force units)
gamma (force/velocity units)
cutoff (distance units) :ul
The last coefficient is optional. If not specified, the global DPD
cutoff is used. Note that sigma is set equal to sqrt(2 T gamma),
where T is the temperature set by the "pair_style"_pair_style.html
command so it does not need to be specified.
+For style {dpd/tstat}, the coefficiencts defined for each pair of
+atoms types via the "pair_coeff"_pair_coeff.html command is the same,
+except that A is not included.
+
:line
[Mixing, shift, table, tail correction, restart, rRESPA info]:
-This pair style does not support mixing. Thus, coefficients for all
+These pair styles do not support mixing. Thus, coefficients for all
I,J pairs must be specified explicitly.
-This pair style does not support the "pair_modify"_pair_modify.html
+These pair styles do not support the "pair_modify"_pair_modify.html
shift option for the energy of the pair interaction.
The "pair_modify"_pair_modify.html table option is not relevant
-for this pair style.
+for these pair styles.
-This pair style does not support the "pair_modify"_pair_modify.html
+These pair style do not support the "pair_modify"_pair_modify.html
tail option for adding long-range tail corrections to energy and
pressure.
-This pair style writes its information to "binary restart
+These pair styles writes their information to "binary restart
files"_restart.html, so pair_style and pair_coeff commands do not need
to be specified in an input script that reads a restart file. Note
that the user-specified random number seed is stored in the restart
file, so when a simulation is restarted, each processor will
re-initialize its random number generator the same way it did
initially. This means the random forces will be random, but will not
be the same as they would have been if the original simulation had
continued past the restart time.
-This pair style can only be used via the {pair} keyword of the
-"run_style respa"_run_style.html command. It does not support the
+These pair styles can only be used via the {pair} keyword of the
+"run_style respa"_run_style.html command. They do not support the
{inner}, {middle}, {outer} keywords.
+The {dpd/tstat} style can ramp its target temperature over multiple
+runs, using the {start} and {stop} keywords of the "run"_run.html
+command. See the "run"_run.html command for details of how to do
+this.
+
:line
[Restrictions:]
The default frequency for rebuilding neighbor lists is every 10 steps
(see the "neigh_modify"_neigh_modify.html command). This may be too
-infrequent for DPD simulations since particles move rapidly and can
-overlap by large amounts. If this setting yields a non-zero number of
-"dangerous" reneighborings (printed at the end of a simulation), you
-should experiment with forcing reneighboring more often and see if
-system energies/trajectories change.
+infrequent for style {dpd} simulations since particles move rapidly
+and can overlap by large amounts. If this setting yields a non-zero
+number of "dangerous" reneighborings (printed at the end of a
+simulation), you should experiment with forcing reneighboring more
+often and see if system energies/trajectories change.
-This pair style requires you to use the "communicate vel
+These pair styles requires you to use the "communicate vel
yes"_communicate.html option so that velocites are stored by ghost
atoms.
[Related commands:]
-"pair_coeff"_pair_coeff.html
+"pair_coeff"_pair_coeff.html, "fix nvt"_fix_nvt.html, "fix
+langevin"_fix_langevin.html
[Default:] none
:line
:link(Groot)
[(Groot)] Groot and Warren, J Chem Phys, 107, 4423-35 (1997).
diff --git a/doc/pair_style.html b/doc/pair_style.html
index 4cda8b470..3f455dd6f 100644
--- a/doc/pair_style.html
+++ b/doc/pair_style.html
@@ -1,178 +1,179 @@
<HTML>
<CENTER><A HREF = "http://lammps.sandia.gov">LAMMPS WWW Site</A> - <A HREF = "Manual.html">LAMMPS Documentation</A> - <A HREF = "Section_commands.html#comm">LAMMPS Commands</A>
</CENTER>
<HR>
<H3>pair_style command
</H3>
<P><B>Syntax:</B>
</P>
<PRE>pair_style style args
</PRE>
<UL><LI>style = one of the styles from the list below
<LI>args = arguments used by a particular style
</UL>
<P><B>Examples:</B>
</P>
<PRE>pair_style lj/cut 2.5
pair_style eam/alloy
pair_style hybrid lj/charmm/coul/long 10.0 eam
pair_style table linear 1000
pair_style none
</PRE>
<P><B>Description:</B>
</P>
<P>Set the formula(s) LAMMPS uses to compute pairwise interactions. In
LAMMPS, pair potentials are defined between pairs of atoms that are
within a cutoff distance and the set of active interactions typically
changes over time. See the <A HREF = "bond_style.html">bond_style</A> command to
define potentials between pairs of bonded atoms, which typically
remain in place for the duration of a simulation.
</P>
<P>In LAMMPS, pairwise force fields encompass a variety of interactions,
some of which include many-body effects, e.g. EAM, Stillinger-Weber,
Tersoff, REBO potentials. They are still classified as "pairwise"
potentials because the set of interacting atoms changes with time
(unlike molecular bonds) and thus a neighbor list is used to find
nearby interacting atoms.
</P>
<P>Hybrid models where specified pairs of atom types interact via
different pair potentials can be setup using the <I>hybrid</I> pair style.
</P>
<P>The coefficients associated with a pair style are typically set for
each pair of atom types, and are specified by the
<A HREF = "pair_coeff.html">pair_coeff</A> command or read from a file by the
<A HREF = "read_data.html">read_data</A> or <A HREF = "read_restart.html">read_restart</A>
commands.
</P>
<P>The <A HREF = "pair_modify.html">pair_modify</A> command sets options for mixing of
type I-J interaction coefficients and adding energy offsets or tail
corrections to Lennard-Jones potentials. Details on these options as
they pertain to individual potentials are described on the doc page
for the potential. Likewise, info on whether the potential
information is stored in a <A HREF = "write_restart.html">restart file</A> is listed
on the potential doc page.
</P>
<P>In the formulas listed for each pair style, <I>E</I> is the energy of a
pairwise interaction between two atoms separated by a distance <I>r</I>.
The force between the atoms is the negative derivative of this
expression.
</P>
<P>If the pair_style command has a cutoff argument, it sets global
cutoffs for all pairs of atom types. The distance(s) can be smaller
or larger than the dimensions of the simulation box.
</P>
<P>Typically, the global cutoff value can be overridden for a specific
pair of atom types by the <A HREF = "pair_coeff.html">pair_coeff</A> command. The
pair style settings (including global cutoffs) can be changed by a
subsequent pair_style command using the same style. This will reset
the cutoffs for all atom type pairs, including those previously set
explicitly by a <A HREF = "pair_coeff.html">pair_coeff</A> command. The exceptions
to this are that pair_style <I>table</I> and <I>hybrid</I> settings cannot be
reset. A new pair_style command for these styles will wipe out all
previously specified pair_coeff values.
</P>
<HR>
<P>Here is an alphabetic list of pair styles defined in LAMMPS. Click on
the style to display the formula it computes, arguments specified in
the pair_style command, and coefficients specified by the associated
<A HREF = "pair_coeff.html">pair_coeff</A> command:
</P>
<UL><LI><A HREF = "pair_none.html">pair_style none</A> - turn off pairwise interactions
<LI><A HREF = "pair_hybrid.html">pair_style hybrid</A> - multiple styles of pairwise interactions
<LI><A HREF = "pair_hybrid.html">pair_style hybrid/overlay</A> - multiple styles of superposed pairwise interactions
</UL>
<UL><LI><A HREF = "pair_airebo.html">pair_style airebo</A> - AI-REBO potential
<LI><A HREF = "pair_born.html">pair_style born/coul/long</A> - Born-Mayer-Huggins with long-range Coulomb
<LI><A HREF = "pair_buck.html">pair_style buck</A> - Buckingham potential
<LI><A HREF = "pair_buck.html">pair_style buck/coul/cut</A> - Buckingham with cutoff Coulomb
<LI><A HREF = "pair_buck.html">pair_style buck/coul/long</A> - Buckingham with long-range Coulomb
<LI><A HREF = "pair_colloid.html">pair_style colloid</A> - integrated colloidal potential
<LI><A HREF = "pair_coul.html">pair_style coul/cut</A> - cutoff Coulombic potential
<LI><A HREF = "pair_coul.html">pair_style coul/debye</A> - cutoff Coulombic potential with Debye screening
<LI><A HREF = "pair_coul.html">pair_style coul/long</A> - long-range Coulombic potential
<LI><A HREF = "pair_dipole.html">pair_style dipole/cut</A> - point dipoles with cutoff
<LI><A HREF = "pair_dpd.html">pair_style dpd</A> - dissipative particle dynamics (DPD)
+<LI><A HREF = "pair_dpd.html">pair_style dpd/tstat</A> - DPD thermostatting
<LI><A HREF = "pair_dsmc.html">pair_style dsmc</A> - Direct Simulation Monte Carlo (DSMC)
<LI><A HREF = "pair_eam.html">pair_style eam</A> - embedded atom method (EAM)
<LI><A HREF = "pair_eam.html">pair_style eam/opt</A> - optimized version of EAM
<LI><A HREF = "pair_eam.html">pair_style eam/alloy</A> - alloy EAM
<LI><A HREF = "pair_eam.html">pair_style eam/alloy/opt</A> - optimized version of alloy EAM
<LI><A HREF = "pair_eam.html">pair_style eam/fs</A> - Finnis-Sinclair EAM
<LI><A HREF = "pair_eam.html">pair_style eam/fs/opt</A> - optimized version of Finnis-Sinclair EAM
<LI><A HREF = "pair_gayberne.html">pair_style gayberne</A> - Gay-Berne ellipsoidal potential
<LI><A HREF = "pair_gayberne.html">pair_style gayberne/gpu</A> - GPU-enabled Gay-Berne ellipsoidal potential
<LI><A HREF = "pair_gran.html">pair_style gran/hertz/history</A> - granular potential with Hertzian interactions
<LI><A HREF = "pair_gran.html">pair_style gran/hooke</A> - granular potential with history effects
<LI><A HREF = "pair_gran.html">pair_style gran/hooke/history</A> - granular potential without history effects
<LI><A HREF = "pair_charmm.html">pair_style lj/charmm/coul/charmm</A> - CHARMM potential with cutoff Coulomb
<LI><A HREF = "pair_charmm.html">pair_style lj/charmm/coul/charmm/implicit</A> - CHARMM for implicit solvent
<LI><A HREF = "pair_charmm.html">pair_style lj/charmm/coul/long</A> - CHARMM with long-range Coulomb
<LI><A HREF = "pair_charmm.html">pair_style lj/charmm/coul/long/opt</A> - optimized version of CHARMM with long-range Coulomb
<LI><A HREF = "pair_class2.html">pair_style lj/class2</A> - COMPASS (class 2) force field with no Coulomb
<LI><A HREF = "pair_class2.html">pair_style lj/class2/coul/cut</A> - COMPASS with cutoff Coulomb
<LI><A HREF = "pair_class2.html">pair_style lj/class2/coul/long</A> - COMPASS with long-range Coulomb
<LI><A HREF = "pair_lj.html">pair_style lj/cut</A> - cutoff Lennard-Jones potential with no Coulomb
<LI><A HREF = "pair_lj.html">pair_style lj/cut/gpu</A> - GPU-enabled version of cutoff LJ
<LI><A HREF = "pair_lj.html">pair_style lj/cut/opt</A> - optimized version of cutoff LJ
<LI><A HREF = "pair_lj.html">pair_style lj/cut/coul/cut</A> - LJ with cutoff Coulomb
<LI><A HREF = "pair_lj.html">pair_style lj/cut/coul/debye</A> - LJ with Debye screening added to Coulomb
<LI><A HREF = "pair_lj.html">pair_style lj/cut/coul/long</A> - LJ with long-range Coulomb
<LI><A HREF = "pair_lj.html">pair_style lj/cut/coul/long/tip4p</A> - LJ with long-range Coulomb for TIP4P water
<LI><A HREF = "pair_lj_expand.html">pair_style lj/expand</A> - Lennard-Jones for variable size particles
<LI><A HREF = "pair_gromacs.html">pair_style lj/gromacs</A> - GROMACS-style Lennard-Jones potential
<LI><A HREF = "pair_gromacs.html">pair_style lj/gromacs/coul/gromacs</A> - GROMACS-style LJ and Coulombic potential
<LI><A HREF = "pair_lj_smooth.html">pair_style lj/smooth</A> - smoothed Lennard-Jones potential
<LI><A HREF = "pair_lj96_cut.html">pair_style lj96/cut</A> - Lennard-Jones 9/6 potential
<LI><A HREF = "pair_lubricate.html">pair_style lubricate</A> - hydrodynamic lubrication forces
<LI><A HREF = "pair_meam.html">pair_style meam</A> - modified embedded atom method (MEAM)
<LI><A HREF = "pair_morse.html">pair_style morse</A> - Morse potential
<LI><A HREF = "pair_morse.html">pair_style morse/opt</A> - optimized version of Morse potential
<LI><A HREF = "pair_peri_pmb.html">pair_style peri/pmb</A> - peridynamic PMB potential
<LI><A HREF = "pair_reax.html">pair_style reax</A> - ReaxFF potential
<LI><A HREF = "pair_resquared.html">pair_style resquared</A> - Everaers RE-Squared ellipsoidal potential
<LI><A HREF = "pair_soft.html">pair_style soft</A> - Soft (cosine) potential
<LI><A HREF = "pair_sw.html">pair_style sw</A> - Stillinger-Weber 3-body potential
<LI><A HREF = "pair_table.html">pair_style table</A> - tabulated pair potential
<LI><A HREF = "pair_tersoff.html">pair_style tersoff</A> - Tersoff 3-body potential
<LI><A HREF = "pair_tersoff_zbl.html">pair_style tersoff/zbl</A> - Tersoff/ZBL 3-body potential
<LI><A HREF = "pair_yukawa.html">pair_style yukawa</A> - Yukawa potential
<LI><A HREF = "pair_yukawa_colloid.html">pair_style yukawa/colloid</A> - screened Yukawa potential for finite-size particles
</UL>
<P>There are also additional pair styles submitted by users which are
included in the LAMMPS distribution. The list of these with links to
the individual styles are given in the pair section of <A HREF = "Section_commands.html#3_5">this
page</A>.
</P>
<HR>
<P><B>Restrictions:</B>
</P>
<P>This command must be used before any coefficients are set by the
<A HREF = "pair_coeff.html">pair_coeff</A>, <A HREF = "read_data.html">read_data</A>, or
<A HREF = "read_restart.html">read_restart</A> commands.
</P>
<P>Some pair styles are part of specific packages. They are only enabled
if LAMMPS was built with that package. See the <A HREF = "Section_start.html#2_3">Making
LAMMPS</A> section for more info on packages. The
doc pages for individual pair potentials tell if it is part of a
package.
</P>
<P><B>Related commands:</B>
</P>
<P><A HREF = "pair_coeff.html">pair_coeff</A>, <A HREF = "read_data.html">read_data</A>,
<A HREF = "pair_modify.html">pair_modify</A>, <A HREF = "kspace_style.html">kspace_style</A>,
<A HREF = "dielectric.html">dielectric</A>, <A HREF = "pair_write.html">pair_write</A>
</P>
<P><B>Default:</B>
</P>
<PRE>pair_style none
</PRE>
</HTML>
diff --git a/doc/pair_style.txt b/doc/pair_style.txt
index a60b9e134..98a04f242 100644
--- a/doc/pair_style.txt
+++ b/doc/pair_style.txt
@@ -1,173 +1,174 @@
"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Section_commands.html#comm)
:line
pair_style command :h3
[Syntax:]
pair_style style args :pre
style = one of the styles from the list below
args = arguments used by a particular style :ul
[Examples:]
pair_style lj/cut 2.5
pair_style eam/alloy
pair_style hybrid lj/charmm/coul/long 10.0 eam
pair_style table linear 1000
pair_style none :pre
[Description:]
Set the formula(s) LAMMPS uses to compute pairwise interactions. In
LAMMPS, pair potentials are defined between pairs of atoms that are
within a cutoff distance and the set of active interactions typically
changes over time. See the "bond_style"_bond_style.html command to
define potentials between pairs of bonded atoms, which typically
remain in place for the duration of a simulation.
In LAMMPS, pairwise force fields encompass a variety of interactions,
some of which include many-body effects, e.g. EAM, Stillinger-Weber,
Tersoff, REBO potentials. They are still classified as "pairwise"
potentials because the set of interacting atoms changes with time
(unlike molecular bonds) and thus a neighbor list is used to find
nearby interacting atoms.
Hybrid models where specified pairs of atom types interact via
different pair potentials can be setup using the {hybrid} pair style.
The coefficients associated with a pair style are typically set for
each pair of atom types, and are specified by the
"pair_coeff"_pair_coeff.html command or read from a file by the
"read_data"_read_data.html or "read_restart"_read_restart.html
commands.
The "pair_modify"_pair_modify.html command sets options for mixing of
type I-J interaction coefficients and adding energy offsets or tail
corrections to Lennard-Jones potentials. Details on these options as
they pertain to individual potentials are described on the doc page
for the potential. Likewise, info on whether the potential
information is stored in a "restart file"_write_restart.html is listed
on the potential doc page.
In the formulas listed for each pair style, {E} is the energy of a
pairwise interaction between two atoms separated by a distance {r}.
The force between the atoms is the negative derivative of this
expression.
If the pair_style command has a cutoff argument, it sets global
cutoffs for all pairs of atom types. The distance(s) can be smaller
or larger than the dimensions of the simulation box.
Typically, the global cutoff value can be overridden for a specific
pair of atom types by the "pair_coeff"_pair_coeff.html command. The
pair style settings (including global cutoffs) can be changed by a
subsequent pair_style command using the same style. This will reset
the cutoffs for all atom type pairs, including those previously set
explicitly by a "pair_coeff"_pair_coeff.html command. The exceptions
to this are that pair_style {table} and {hybrid} settings cannot be
reset. A new pair_style command for these styles will wipe out all
previously specified pair_coeff values.
:line
Here is an alphabetic list of pair styles defined in LAMMPS. Click on
the style to display the formula it computes, arguments specified in
the pair_style command, and coefficients specified by the associated
"pair_coeff"_pair_coeff.html command:
"pair_style none"_pair_none.html - turn off pairwise interactions
"pair_style hybrid"_pair_hybrid.html - multiple styles of pairwise interactions
"pair_style hybrid/overlay"_pair_hybrid.html - multiple styles of superposed pairwise interactions :ul
"pair_style airebo"_pair_airebo.html - AI-REBO potential
"pair_style born/coul/long"_pair_born.html - Born-Mayer-Huggins with long-range Coulomb
"pair_style buck"_pair_buck.html - Buckingham potential
"pair_style buck/coul/cut"_pair_buck.html - Buckingham with cutoff Coulomb
"pair_style buck/coul/long"_pair_buck.html - Buckingham with long-range Coulomb
"pair_style colloid"_pair_colloid.html - integrated colloidal potential
"pair_style coul/cut"_pair_coul.html - cutoff Coulombic potential
"pair_style coul/debye"_pair_coul.html - cutoff Coulombic potential with Debye screening
"pair_style coul/long"_pair_coul.html - long-range Coulombic potential
"pair_style dipole/cut"_pair_dipole.html - point dipoles with cutoff
"pair_style dpd"_pair_dpd.html - dissipative particle dynamics (DPD)
+"pair_style dpd/tstat"_pair_dpd.html - DPD thermostatting
"pair_style dsmc"_pair_dsmc.html - Direct Simulation Monte Carlo (DSMC)
"pair_style eam"_pair_eam.html - embedded atom method (EAM)
"pair_style eam/opt"_pair_eam.html - optimized version of EAM
"pair_style eam/alloy"_pair_eam.html - alloy EAM
"pair_style eam/alloy/opt"_pair_eam.html - optimized version of alloy EAM
"pair_style eam/fs"_pair_eam.html - Finnis-Sinclair EAM
"pair_style eam/fs/opt"_pair_eam.html - optimized version of Finnis-Sinclair EAM
"pair_style gayberne"_pair_gayberne.html - Gay-Berne ellipsoidal potential
"pair_style gayberne/gpu"_pair_gayberne.html - GPU-enabled Gay-Berne ellipsoidal potential
"pair_style gran/hertz/history"_pair_gran.html - granular potential with Hertzian interactions
"pair_style gran/hooke"_pair_gran.html - granular potential with history effects
"pair_style gran/hooke/history"_pair_gran.html - granular potential without history effects
"pair_style lj/charmm/coul/charmm"_pair_charmm.html - CHARMM potential with cutoff Coulomb
"pair_style lj/charmm/coul/charmm/implicit"_pair_charmm.html - CHARMM for implicit solvent
"pair_style lj/charmm/coul/long"_pair_charmm.html - CHARMM with long-range Coulomb
"pair_style lj/charmm/coul/long/opt"_pair_charmm.html - optimized version of CHARMM with long-range Coulomb
"pair_style lj/class2"_pair_class2.html - COMPASS (class 2) force field with no Coulomb
"pair_style lj/class2/coul/cut"_pair_class2.html - COMPASS with cutoff Coulomb
"pair_style lj/class2/coul/long"_pair_class2.html - COMPASS with long-range Coulomb
"pair_style lj/cut"_pair_lj.html - cutoff Lennard-Jones potential with no Coulomb
"pair_style lj/cut/gpu"_pair_lj.html - GPU-enabled version of cutoff LJ
"pair_style lj/cut/opt"_pair_lj.html - optimized version of cutoff LJ
"pair_style lj/cut/coul/cut"_pair_lj.html - LJ with cutoff Coulomb
"pair_style lj/cut/coul/debye"_pair_lj.html - LJ with Debye screening added to Coulomb
"pair_style lj/cut/coul/long"_pair_lj.html - LJ with long-range Coulomb
"pair_style lj/cut/coul/long/tip4p"_pair_lj.html - LJ with long-range Coulomb for TIP4P water
"pair_style lj/expand"_pair_lj_expand.html - Lennard-Jones for variable size particles
"pair_style lj/gromacs"_pair_gromacs.html - GROMACS-style Lennard-Jones potential
"pair_style lj/gromacs/coul/gromacs"_pair_gromacs.html - GROMACS-style LJ and Coulombic potential
"pair_style lj/smooth"_pair_lj_smooth.html - smoothed Lennard-Jones potential
"pair_style lj96/cut"_pair_lj96_cut.html - Lennard-Jones 9/6 potential
"pair_style lubricate"_pair_lubricate.html - hydrodynamic lubrication forces
"pair_style meam"_pair_meam.html - modified embedded atom method (MEAM)
"pair_style morse"_pair_morse.html - Morse potential
"pair_style morse/opt"_pair_morse.html - optimized version of Morse potential
"pair_style peri/pmb"_pair_peri_pmb.html - peridynamic PMB potential
"pair_style reax"_pair_reax.html - ReaxFF potential
"pair_style resquared"_pair_resquared.html - Everaers RE-Squared ellipsoidal potential
"pair_style soft"_pair_soft.html - Soft (cosine) potential
"pair_style sw"_pair_sw.html - Stillinger-Weber 3-body potential
"pair_style table"_pair_table.html - tabulated pair potential
"pair_style tersoff"_pair_tersoff.html - Tersoff 3-body potential
"pair_style tersoff/zbl"_pair_tersoff_zbl.html - Tersoff/ZBL 3-body potential
"pair_style yukawa"_pair_yukawa.html - Yukawa potential
"pair_style yukawa/colloid"_pair_yukawa_colloid.html - screened Yukawa potential for finite-size particles :ul
There are also additional pair styles submitted by users which are
included in the LAMMPS distribution. The list of these with links to
the individual styles are given in the pair section of "this
page"_Section_commands.html#3_5.
:line
[Restrictions:]
This command must be used before any coefficients are set by the
"pair_coeff"_pair_coeff.html, "read_data"_read_data.html, or
"read_restart"_read_restart.html commands.
Some pair styles are part of specific packages. They are only enabled
if LAMMPS was built with that package. See the "Making
LAMMPS"_Section_start.html#2_3 section for more info on packages. The
doc pages for individual pair potentials tell if it is part of a
package.
[Related commands:]
"pair_coeff"_pair_coeff.html, "read_data"_read_data.html,
"pair_modify"_pair_modify.html, "kspace_style"_kspace_style.html,
"dielectric"_dielectric.html, "pair_write"_pair_write.html
[Default:]
pair_style none :pre