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lammps/doc/pair_class2.txt
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pair_class2.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
pair_style lj/class2 command :h3
pair_style lj/class2/coul/cut command :h3
pair_style lj/class2/coul/long command :h3
[Syntax:]
pair_style style args :pre
style = {lj/class2} or {lj/class2/coul/cut} or {lj/class2/coul/long}
args = list of arguments for a particular style :ul
{lj/class2} args = cutoff
cutoff = global cutoff for class 2 interactions (distance units)
{lj/class2/coul/cut} args = cutoff (cutoff2)
cutoff = global cutoff for class 2 (and Coulombic if only 1 arg) (distance units)
cutoff2 = global cutoff for Coulombic (optional) (distance units)
{lj/class2/coul/long} args = cutoff (cutoff2)
cutoff = global cutoff for class 2 (and Coulombic if only 1 arg) (distance units)
cutoff2 = global cutoff for Coulombic (optional) (distance units) :pre
[Examples:]
pair_style lj/class2 10.0
pair_coeff * * 100.0 2.5
pair_coeff 1 2* 100.0 2.5 9.0 :pre
pair_style lj/class2/coul/cut 10.0
pair_style lj/class2/coul/cut 10.0 8.0
pair_coeff * * 100.0 3.0
pair_coeff 1 1 100.0 3.5 9.0
pair_coeff 1 1 100.0 3.5 9.0 9.0 :pre
pair_style lj/class2/coul/long 10.0
pair_style lj/class2/coul/long 10.0 8.0
pair_coeff * * 100.0 3.0
pair_coeff 1 1 100.0 3.5 9.0 :pre
[Description:]
The {lj/class2} styles compute a 6/9 Lennard-Jones potential given by
:c,image(Eqs/pair_class2.jpg)
Rc is the cutoff.
The {lj/class2/coul/cut} and {lj/class2/coul/long} styles add a
Coulombic term as described for the "lj/cut"_pair_lj.html pair
styles.
See "(Sun)"_#Sun for a description of the COMPASS class2 force field.
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, or by mixing as described below:
epsilon (energy units)
sigma (distance units)
cutoff1 (distance units)
cutoff2 (distance units) :ul
The latter 2 coefficients are optional. If not specified, the global
class 2 and Coulombic cutoffs are used. If only one cutoff is
specified, it is used as the cutoff for both class 2 and Coulombic
interactions for this type pair. If both coefficients are specified,
they are used as the class 2 and Coulombic cutoffs for this type pair.
You cannot specify 2 cutoffs for style {lj/class2}, since it has no
Coulombic terms.
For {lj/class2/coul/long} only the class 2 cutoff can be specified
since a Coulombic cutoff cannot be specified for an individual I,J
type pair. All type pairs use the same global Coulombic cutoff
specified in the pair_style command.
: line
If the pair_coeff command is not used to define coefficients for a
particular I != J type pair, the mixing rule for epsilon and sigma for
all class2 potentials is to use the {sixthpower} formulas documented
by the "pair_modify"_pair_modify.html command. The "pair_modify
mix"_pair_modify.html setting is thus ignored for class2 potentials
for epsilon and sigma. However it is still followed for mixing the
cutoff distance.
[Mixing, shift, table, tail correction, per-atom energy/stress,
restart, and rRESPA info]:
For atom type pairs I,J and I != J, the epsilon and sigma coefficients
and cutoff distance for all of the lj/class2 pair styles can be mixed.
Epsilon and sigma are always mixed with the value {sixthpower}. The
cutoff distance is mixed by whatever option is set by the pair_modify
command (default = geometric). See the "pair_modify" command for
details.
All of the lj/class2 pair styles support the
"pair_modify"_pair_modify.html shift option for the energy of the
Lennard-Jones portion of the pair interaction.
The {lj/class2/coul/long} pair style does not support the
"pair_modify"_pair_modify.html table option since a tabulation
capability has not yet been added to this potential.
All of the lj/class2 pair styles support the
"pair_modify"_pair_modify.html tail option for adding a long-range
tail correction to the energy and pressure of the Lennard-Jones
portion of the pair interaction.
All of the lj/class2 pair styles can calculate per-atom energy and
stress, as used by the "compute epair/atom"_compute_epair_atom.html,
"compute stress/atom"_compute_stress_atom.html, and "dump
custom"_dump.html commands.
All of the lj/class2 pair styles write 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.
All of the lj/class2 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 of the "run_style
command"_run_style.html.
[Restrictions:]
All of these pair styles are part of the "class2" package. They are
only enabled if LAMMPS was built with that package. See the "Making
LAMMPS"_Section_start.html#2_3 section for more info.
[Related commands:]
"pair_coeff"_pair_coeff.html
[Default:] none
:line
:link(Sun)
[(Sun)] Sun, J Phys Chem B 102, 7338-7364 (1998).
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