forked from lijiext/lammps
139 lines
4.7 KiB
Plaintext
139 lines
4.7 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 dsmc command :h3
|
|
|
|
[Syntax:]
|
|
|
|
pair_style dsmc max_cell_size seed weighting Tref Nrecompute Nsample :pre
|
|
|
|
max_cell_size = global maximum cell size for DSMC interactions (distance units)
|
|
seed = random # seed (positive integer)
|
|
weighting = macroparticle weighting
|
|
Tref = reference temperature (temperature units)
|
|
Nrecompute = recompute v*sigma_max every this many timesteps (timesteps)
|
|
Nsample = sample this many times in recomputing v*sigma_max :ul
|
|
|
|
[Examples:]
|
|
|
|
pair_style dsmc 2.5 34387 10 1.0 100 20
|
|
pair_coeff * * 1.0
|
|
pair_coeff 1 1 1.0 :pre
|
|
|
|
[Description:]
|
|
|
|
Style {dsmc} computes collisions between pairs of particles for a
|
|
direct simulation Monte Carlo (DSMC) model following the exposition in
|
|
"(Bird)"_#Bird. Each collision resets the velocities of the two
|
|
particles involved. The number of pairwise collisions for each pair
|
|
or particle types and the length scale within which they occur are
|
|
determined by the parameters of the pair_style and pair_coeff
|
|
commands.
|
|
|
|
Stochastic collisions are performed using the variable hard sphere
|
|
(VHS) approach, with the user-defined {max_cell_size} value used as
|
|
the maximum DSMC cell size, and reference cross-sections for
|
|
collisions given using the pair_coeff command.
|
|
|
|
There is no pairwise energy or virial contributions associated with
|
|
this pair style.
|
|
|
|
The following coefficient 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:
|
|
|
|
sigma (area units, i.e. distance-squared) :ul
|
|
|
|
The global DSMC {max_cell_size} determines the maximum cell length
|
|
used in the DSMC calculation. A structured mesh is overlayed on the
|
|
simulation box such that an integer number of cells are created in
|
|
each direction for each processor's sub-domain. Cell lengths are
|
|
adjusted up to the user-specified maximum cell size.
|
|
|
|
:line
|
|
|
|
To perform a DSMC simulation with LAMMPS, several additional options
|
|
should be set in your input script, though LAMMPS does not check for
|
|
these settings.
|
|
|
|
Since this pair style does not compute particle forces, you should use
|
|
the "fix nve/noforce" time integration fix for the DSMC particles,
|
|
e.g.
|
|
|
|
fix 1 all nve/noforce :pre
|
|
|
|
This pair style assumes that all particles will communicated to
|
|
neighboring processors every timestep as they move. This makes it
|
|
possible to perform all collisions between pairs of particles that are
|
|
on the same processor. To ensure this occurs, you should use
|
|
these commands:
|
|
|
|
neighbor 0.0 bin
|
|
neigh_modify every 1 delay 0 check no
|
|
communicate single cutoff 0.0 :pre
|
|
|
|
These commands insure that LAMMPS communicates particles to
|
|
neighboring processors every timestep and that no ghost atoms are
|
|
created. The output statistics for a simulation run should indicate
|
|
there are no ghost particles or neighbors.
|
|
|
|
:line
|
|
|
|
[Mixing, shift, table, tail correction, restart, rRESPA info]:
|
|
|
|
This pair style does 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
|
|
shift option for the energy of the pair interaction.
|
|
|
|
The "pair_modify"_pair_modify.html table option is not relevant
|
|
for this pair style.
|
|
|
|
This pair style does 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
|
|
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
|
|
{inner}, {middle}, {outer} keywords.
|
|
|
|
:line
|
|
|
|
[Restrictions:]
|
|
|
|
This style is part of the MC 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.
|
|
|
|
[Related commands:]
|
|
|
|
"pair_coeff"_pair_coeff.html, "fix nve/noforce"_fix_nve_noforce.html,
|
|
"neigh_modify"_neigh_modify.html, "neighbor"_neighbor.html,
|
|
"communicate"_communicate.html
|
|
|
|
[Default:] none
|
|
|
|
:line
|
|
|
|
:link(Bird)
|
|
[(Bird)] G. A. Bird, "Molecular Gas Dynamics and the Direct Simulation
|
|
of Gas Flows" (1994).
|