lammps/doc/pair_soft.txt

89 lines
2.6 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 soft command :h3
[Syntax:]
pair_style soft cutoff :pre
cutoff = global cutoff for soft interactions (distance units) :ul
[Examples:]
pair_style soft 2.5
pair_coeff * * 0.0 60.0
pair_coeff 1 1 0.0 60.0 3.0 :pre
[Description:]
Style {soft} computes pairwise interactions with the formula
:c,image(Eqs/pair_soft.jpg)
It is useful for pushing apart overlapping atoms, since it does not
blow up as r goes to 0. A is a pre-factor that varies in time from
the start to the end of the run. The "run"_run.html command documents
how to make the ramping take place across multiple runs. Rc is the
cutoff.
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:
Astart (energy units)
Astop (energy units)
cutoff (distance units) :ul
Astart and Astop are the values of the prefactor at the start and end
of the next run. At intermediate times the value of A will be ramped
between these 2 values. Note that before performing a 2nd run, you
will want to adjust the values of Astart and Astop for all type pairs,
or switch to a new pair style.
The last coefficient is optional. If not specified, the global soft
cutoff is used.
:line
[Mixing, shift, table, tail correction, per-atom energy/stress, and
restart info]:
For atom type pairs I,J and I != J, the Astart, Astop coefficients and
cutoff distance for this pair style can be mixed. Astart and Atop are
always mixed via a {geometric} rule. The cutoff is mixed according to
the pair_modify mix value. The default mix value is {geometric}. See
the "pair_modify" command for details.
This pair styles does not support the "pair_modify"_pair_modify.html
shift option, since the pair interaction is goes to 0.0 at the cutoff.
The "pair_modify"_pair_modify.html table and tail options are not
relevant for this pair style.
This pair style 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.
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.
:line
[Restrictions:] none
[Related commands:]
"pair_coeff"_pair_coeff.html
[Default:] none