forked from lijiext/lammps
120 lines
4.2 KiB
Plaintext
120 lines
4.2 KiB
Plaintext
"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 body command :h3
|
|
|
|
[Syntax:]
|
|
|
|
pair_style body cutoff :pre
|
|
|
|
cutoff = global cutoff for interactions (distance units)
|
|
|
|
[Examples:]
|
|
|
|
pair_style body 3.0
|
|
pair_coeff * * 1.0 1.0
|
|
pair_coeff 1 1 1.0 1.5 2.5 :pre
|
|
|
|
[Description:]
|
|
|
|
Style {body} is for use with body particles and calculates pairwise
|
|
body/body interactions as well as interactions between body and
|
|
point-particles. See "Section_howto 14"_Section_howto.html#howto_14
|
|
of the manual and the "body"_body.html doc page for more details on
|
|
using body particles.
|
|
|
|
This pair style is designed for use with the "nparticle" body style,
|
|
which is specified as an argument to the "atom-style body" command.
|
|
See the "body"_body.html doc page for more details about the body
|
|
styles LAMMPS supports. The "nparticle" style treats a body particle
|
|
as a rigid body composed of N sub-particles.
|
|
|
|
The coordinates of a body particle are its center-of-mass (COM). If
|
|
the COMs of a pair of body particles are within the cutoff (global or
|
|
type-specific, as specified above), then all interactions between
|
|
pairs of sub-particles in the two body particles are computed.
|
|
E.g. if the first body particle has 3 sub-particles, and the second
|
|
has 10, then 30 interactions are computed and summed to yield the
|
|
total force and torque on each body particle.
|
|
|
|
IMPORTANT NOTE: In the example just described, all 30 interactions are
|
|
computed even if the distance between a particular pair of
|
|
sub-particles is greater than the cutoff. Likewise, no interaction
|
|
between two body particles is computed if the two COMs are further
|
|
apart than the cutoff, even if the distance between some pairs of
|
|
their sub-particles is within the cutoff. Thus care should be used in
|
|
defining the cutoff distances for body particles, depending on their
|
|
shape and size.
|
|
|
|
Similar rules apply for a body particle interacting with a point
|
|
particle. The distance between the two particles is calculated using
|
|
the COM of the body particle and the position of the point particle.
|
|
If the distance is within the cutoff and the body particle has N
|
|
sub-particles, then N interactions with the point particle are
|
|
computed and summed. If the distance is not within the cutoff, no
|
|
interactions between the body and point particle are computed.
|
|
|
|
The interaction between two sub-particles, or a sub-particle and point
|
|
particle, or betwee two point particles is computed as a Lennard-Jones
|
|
interaction, using the standard formula
|
|
|
|
:c,image(Eqs/pair_lj.jpg)
|
|
|
|
where Rc is the cutoff. As explained above, an interaction involving
|
|
one or two body sub-particles may be computed even for r > Rc.
|
|
|
|
For style {body}, 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:
|
|
|
|
epsilon (energy units)
|
|
sigma (distance units)
|
|
cutoff (distance units) :ul
|
|
|
|
The last coefficient is optional. If not specified, the global cutoff
|
|
is used.
|
|
|
|
:line
|
|
|
|
[Mixing, shift, table, tail correction, restart, rRESPA info]:
|
|
|
|
For atom type pairs I,J and I != J, the epsilon and sigma coefficients
|
|
and cutoff distance for all of this pair style can be mixed. The
|
|
default mix value is {geometric}. See the "pair_modify" command for
|
|
details.
|
|
|
|
This pair style does not support the "pair_modify"_pair_modify.html
|
|
shift, table, and tail options.
|
|
|
|
This pair style does not write its information to "binary restart
|
|
files"_restart.html.
|
|
|
|
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
|
|
{inner}, {middle}, {outer} keywords.
|
|
|
|
:line
|
|
|
|
[Restrictions:]
|
|
|
|
This style is part of the BODY package. It is only enabled if LAMMPS
|
|
was built with that package. See the "Making
|
|
LAMMPS"_Section_start.html#2_3 section for more info.
|
|
|
|
Defining particles to be bodies so they participate in body/body or
|
|
body/particle interactions requires the use of the "atom_style
|
|
body"_atom_style.html command.
|
|
|
|
[Related commands:]
|
|
|
|
"pair_coeff"_pair_coeff.html, "fix_rigid"_fix_rigid.html
|
|
|
|
[Default:] none
|