forked from lijiext/lammps
137 lines
4.8 KiB
Plaintext
137 lines
4.8 KiB
Plaintext
"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
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:link(lws,http://lammps.sandia.gov)
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:link(ld,Manual.html)
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:link(lc,Section_commands.html#comm)
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:line
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pair_style soft command :h3
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pair_style soft/gpu command :h3
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pair_style soft/omp command :h3
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[Syntax:]
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pair_style soft cutoff :pre
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cutoff = global cutoff for soft interactions (distance units) :ul
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[Examples:]
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pair_style soft 2.5
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pair_coeff * * 10.0
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pair_coeff 1 1 10.0 3.0 :pre
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pair_style soft 2.5
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pair_coeff * * 0.0
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variable prefactor equal ramp(0,30)
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fix 1 all adapt 1 pair soft a * * v_prefactor :pre
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[Description:]
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Style {soft} computes pairwise interactions with the formula
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:c,image(Eqs/pair_soft.jpg)
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It is useful for pushing apart overlapping atoms, since it does not
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blow up as r goes to 0. A is a pre-factor that can be made to vary in
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time from the start to the end of the run (see discussion below),
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e.g. to start with a very soft potential and slowly harden the
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interactions over time. Rc is the cutoff. See the "fix
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nve/limit"_fix_nve_limit.html command for another way to push apart
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overlapping atoms.
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The following coefficients must be defined for each pair of atom types
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via the "pair_coeff"_pair_coeff.html command as in the examples above,
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or in the data file or restart files read by the
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"read_data"_read_data.html or "read_restart"_read_restart.html
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commands, or by mixing as described below:
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A (energy units)
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cutoff (distance units) :ul
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The last coefficient is optional. If not specified, the global soft
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cutoff is used.
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IMPORTANT NOTE: The syntax for "pair_coeff"_pair_coeff.html with a
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single A coeff is different in the current version of LAMMPS than in
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older versions which took two values, Astart and Astop, to ramp
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between them. This functionality is now available in a more general
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form through the "fix adapt"_fix_adapt.html command, as explained
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below. Note that if you use an old input script and specify Astart
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and Astop without a cutoff, then LAMMPS will interpret that as A and a
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cutoff, which is probabably not what you want.
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The "fix adapt"_fix_adapt.html command can be used to vary A for one
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or more pair types over the course of a simulation, in which case
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pair_coeff settings for A must still be specified, but will be
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overridden. For example these commands will vary the prefactor A for
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all pairwise interactions from 0.0 at the beginning to 30.0 at the end
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of a run:
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variable prefactor equal ramp(0,30)
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fix 1 all adapt 1 pair soft a * * v_prefactor :pre
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Note that a formula defined by an "equal-style variable"_variable.html
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can use the current timestep, elapsed time in the current run, elapsed
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time since the beginning of a series of runs, as well as access other
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variables.
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:line
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Styles with a {cuda}, {gpu}, {intel}, {kk}, {omp}, or {opt} suffix are
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functionally the same as the corresponding style without the suffix.
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They have been optimized to run faster, depending on your available
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hardware, as discussed in "Section_accelerate"_Section_accelerate.html
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of the manual. The accelerated styles take the same arguments and
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should produce the same results, except for round-off and precision
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issues.
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These accelerated styles are part of the USER-CUDA, GPU, USER-INTEL,
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KOKKOS, USER-OMP and OPT packages, respectively. They are only
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enabled if LAMMPS was built with those packages. See the "Making
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LAMMPS"_Section_start.html#start_3 section for more info.
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You can specify the accelerated styles explicitly in your input script
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by including their suffix, or you can use the "-suffix command-line
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switch"_Section_start.html#start_7 when you invoke LAMMPS, or you can
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use the "suffix"_suffix.html command in your input script.
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See "Section_accelerate"_Section_accelerate.html of the manual for
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more instructions on how to use the accelerated styles effectively.
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:line
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[Mixing, shift, table, tail correction, restart, rRESPA info]:
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For atom type pairs I,J and I != J, the A coefficient and cutoff
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distance for this pair style can be mixed. A is always mixed via a
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{geometric} rule. The cutoff is mixed according to the pair_modify
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mix value. The default mix value is {geometric}. See the
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"pair_modify" command for details.
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This pair style does not support the "pair_modify"_pair_modify.html
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shift option, since the pair interaction goes to 0.0 at the cutoff.
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The "pair_modify"_pair_modify.html table and tail options are not
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relevant for this pair style.
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This pair style writes its information to "binary restart
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files"_restart.html, so pair_style and pair_coeff commands do not need
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to be specified in an input script that reads a restart file.
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This pair style can only be used via the {pair} keyword of the
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"run_style respa"_run_style.html command. It does not support the
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{inner}, {middle}, {outer} keywords.
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:line
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[Restrictions:] none
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[Related commands:]
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"pair_coeff"_pair_coeff.html, "fix nve/limit"_fix_nve_limit.html, "fix
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adapt"_fix_adapt.html
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[Default:] none
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