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lammps/doc/src/fix_append_atoms.txt
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"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 append/atoms command :h3
[Syntax:]
fix ID group-ID append/atoms face ... keyword value ... :pre
ID, group-ID are documented in "fix"_fix.html command :ulb,l
append/atoms = style name of this fix command :l
face = {zhi} :l
zero or more keyword/value pairs may be appended :l
keyword = {basis} or {size} or {freq} or {temp} or {random} or {units} :l
{basis} values = M itype
M = which basis atom
itype = atom type (1-N) to assign to this basis atom
{size} args = Lz
Lz = z size of lattice region appended in a single event(distance units)
{freq} args = freq
freq = the number of timesteps between append events
{temp} args = target damp seed extent
target = target temperature for the region between zhi-extent and zhi (temperature units)
damp = damping parameter (time units)
seed = random number seed for langevin kicks
extent = extent of thermostated region (distance units)
{random} args = xmax ymax zmax seed
{xmax}, {ymax}, {zmax} = maximum displacement in particular direction (distance units)
{seed} = random number seed for random displacement
{units} value = {lattice} or {box}
{lattice} = the wall position is defined in lattice units
{box} = the wall position is defined in simulation box units :pre
:ule
[Examples:]
fix 1 all append/atoms zhi size 5.0 freq 295 units lattice
fix 4 all append/atoms zhi size 15.0 freq 5 units box
fix A all append/atoms zhi size 1.0 freq 1000 units lattice :pre
[Description:]
This fix creates atoms on a lattice, appended on the zhi edge of the
system box. This can be useful when a shock or wave is propagating
from zlo. This allows the system to grow with time to accommodate an
expanding wave. A simulation box must already exist, which is
typically created via the "create_box"_create_box.html command.
Before using this command, a lattice must also be defined using the
"lattice"_lattice.html command.
This fix will automatically freeze atoms on the zhi edge of the
system, so that overlaps are avoided when new atoms are appended.
The {basis} keyword specifies an atom type that will be assigned to
specific basis atoms as they are created. See the
"lattice"_lattice.html command for specifics on how basis atoms are
defined for the unit cell of the lattice. By default, all created
atoms are assigned type = 1 unless this keyword specifies differently.
The {size} keyword defines the size in z of the chunk of material to
be added.
The {random} keyword will give the atoms random displacements around
their lattice points to simulate some initial temperature.
The {temp} keyword will cause a region to be thermostated with a
Langevin thermostat on the zhi boundary. The size of the region is
measured from zhi and is set with the {extent} argument.
The {units} keyword determines the meaning of the distance units used
to define a wall position, but only when a numeric constant is used.
A {box} value selects standard distance units as defined by the
"units"_units.html command, e.g. Angstroms for units = real or metal.
A {lattice} value means the distance units are in lattice spacings.
The "lattice"_lattice.html command must have been previously used to
define the lattice spacings.
:line
[Restart, fix_modify, output, run start/stop, minimize info:]
No information about this fix is written to "binary restart
files"_restart.html. None of the "fix_modify"_fix_modify.html options
are relevant to this fix. No global or per-atom quantities are stored
by this fix for access by various "output
commands"_Section_howto.html#howto_15. No parameter of this fix can
be used with the {start/stop} keywords of the "run"_run.html command.
This fix is not invoked during "energy minimization"_minimize.html.
[Restrictions:]
This fix style is part of the SHOCK package. It is only enabled if
LAMMPS was built with that package. See the "Making
LAMMPS"_Section_start.html#start_3 section for more info.
The boundary on which atoms are added with append/atoms must be
shrink/minimum. The opposite boundary may be any boundary type other
than periodic.
[Related commands:]
"fix wall/piston"_fix_wall_piston.html command
[Default:]
The keyword defaults are size = 0.0, freq = 0, units = lattice. All
added atoms are of type 1 unless the basis keyword is used.
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