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 buck command :h3
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pair_style buck/coul/cut command :h3
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pair_style buck/coul/long command :h3
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[Syntax:]
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pair_style style args :pre
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style = {buck} or {buck/coul/cut} or {buck/coul/long}
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args = list of arguments for a particular style :ul
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{buck} args = cutoff
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cutoff = global cutoff for Buckingham interactions (distance units)
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{buck/coul/cut} args = cutoff (cutoff2)
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cutoff = global cutoff for Buckingham (and Coulombic if only 1 arg) (distance units)
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cutoff2 = global cutoff for Coulombic (optional) (distance units)
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{buck/coul/long} args = cutoff (cutoff2)
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cutoff = global cutoff for Buckingham (and Coulombic if only 1 arg) (distance units)
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cutoff2 = global cutoff for Coulombic (optional) (distance units) :pre
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[Examples:]
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pair_style buck 2.5
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pair_coeff * * 100.0 1.5 200.0
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pair_coeff * * 100.0 1.5 200.0 3.0 :pre
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pair_style buck/coul/cut 10.0
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pair_style buck/coul/cut 10.0 8.0
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pair_coeff * * 100.0 1.5 200.0
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pair_coeff 1 1 100.0 1.5 200.0 9.0
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pair_coeff 1 1 100.0 1.5 200.0 9.0 8.0 :pre
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pair_style buck/coul/long 10.0
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pair_style buck/coul/long 10.0 8.0
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pair_coeff * * 100.0 1.5 200.0
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pair_coeff 1 1 100.0 1.5 200.0 9.0 :pre
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[Description:]
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The {buck} style computes a Buckingham potential (exp/6 instead of
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Lennard-Jones 12/6) given by
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:c,image(Eqs/pair_buck.jpg)
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where rho is an ionic-pair dependent length parameter, and Rc is the
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cutoff.
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The {buck/coul/cut} and {buck/coul/long} styles add a Coulombic term
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as described for the "lj/cut"_pair_lj.html pair styles. For
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{buck/coul/long}, an additional damping factor is applied to the
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Coulombic term so it can be used in conjunction with the
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"kspace_style"_kspace_style.html command and its {ewald} or {pppm}
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option. The Coulombic cutoff specified for this style means that
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pairwise interactions within this distance are computed directly;
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interactions outside that distance are computed in reciprocal space.
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If one cutoff is specified for the {born/coul/cut} and
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{born/coulk/long} styles, it is used for both the A,C and Coulombic
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terms. If two cutoffs are specified, the first is used as the cutoff
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for the A,C terms, and the second is the cutoff for the Coulombic
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term.
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Note that these potentials are related to the "Born-Mayer-Huggins
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potential"_pair_born.html.
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The following coefficients must be defined for each pair of atoms
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types via the "pair_coeff"_pair_coeff.html command as in the examples
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above, 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:
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A (energy units)
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rho (distance units)
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C (energy-distance^6 units)
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cutoff (distance units)
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cutoff2 (distance units) :ul
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The second coefficient, rho, must be greater than zero.
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The latter 2 coefficients are optional. If not specified, the global
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A,C and Coulombic cutoffs are used. If only one cutoff is specified,
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it is used as the cutoff for both A,C and Coulombic interactions for
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this type pair. If both coefficients are specified, they are used as
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the A,C and Coulombic cutoffs for this type pair. You cannot specify
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2 cutoffs for style {buck}, since it has no Coulombic terms.
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For {buck/coul/long} only the LJ cutoff can be specified since a
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Coulombic cutoff cannot be specified for an individual I,J type pair.
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All type pairs use the same global Coulombic cutoff specified in the
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pair_style command.
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:line
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[Mixing, shift, table, tail correction, restart, rRESPA info]:
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These pair styles do not support mixing. Thus, coefficients for all
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I,J pairs must be specified explicitly.
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These styles support the "pair_modify"_pair_modify.html shift option
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for the energy of the exp() and 1/r^6 portion of the pair interaction.
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The {buck/coul/long} pair style does not support the
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"pair_modify"_pair_modify.html table option since a tabulation
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capability has not yet been added to this potential.
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These styles support the pair_modify tail option for adding long-range
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tail corrections to energy and pressure for the A,C terms in the
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pair interaction.
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These styles write their 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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These styles can only be used via the {pair} keyword of the "run_style
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respa"_run_style.html command. They do not support the {inner},
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{middle}, {outer} keywords.
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[Restrictions:]
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The {buck/coul/long} style is part of the "kspace" package. It is
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only enabled if LAMMPS was built with that package (which it is by
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default). See the "Making LAMMPS"_Section_start.html#2_3 section for
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more info.
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[Related commands:]
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"pair_coeff"_pair_coeff.html, "pair_style born"_pair_born.html
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[Default:] none
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