forked from lijiext/lammps
123 lines
4.0 KiB
Plaintext
123 lines
4.0 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 coul/cut command :h3
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pair_style coul/long command :h3
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[Syntax:]
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pair_style coul/cut cutoff
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pair_style coul/long cutoff :pre
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cutoff = global cutoff for Coulombic interactions :ul
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[Examples:]
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pair_style coul/cut 2.5
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pair_coeff * *
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pair_coeff 2 2 3.5 :pre
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pair_style coul/long 10.0
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pair_coeff * * :pre
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[Description:]
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The {coul/cut} style computes the standard Coulombic interaction
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potential given by
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:c,image(Eqs/pair_coulomb.jpg)
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where C is an energy-conversion constant, Qi and Qj are the charges on
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the 2 atoms, and epsilon is the dielectric constant which can be set
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by the "dielectric"_dielectric.html command. The cutoff Rc truncates
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the interaction distance.
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Style {coul/long} computes the same Coulombic interactions as style
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{coul/cut} except that an additional damping factor is applied so it
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can be used in conjunction with the "kspace_style"_kspace_style.html
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command and its {ewald} or {pppm} option. The Coulombic cutoff
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specified for this style means that pairwise interactions within this
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distance are computed directly; interactions outside that distance are
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computed in reciprocal space.
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These potentials are designed to be combined with other pair
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potentials via the "pair_style hybrid/overlay"_pair_hybrid.html
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command. This is because they have no repulsive core. Hence if they
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are used by themselves, there will be no repulsion to keep two
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oppositely charged particles from overlapping each other.
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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, or by mixing as described below:
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cutoff (distance units) :ul
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For {coul/cut}, the cutoff coefficient is optional. If it is not used
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(as in som of the examples above), the default global value specified
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in the pair_style command is used.
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For {coul/long} no cutoff can be specified for an individual I,J type
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pair via the pair_coeff command. All type pairs use the same global
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Coulombic cutoff specified in the pair_style command.
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:line
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[Mixing, shift, table, tail correction, per-atom energy/stress,
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restart, rRESPA info]:
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For atom type pairs I,J and I != J, the cutoff distance for the
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{coul/cut} style can be mixed. The default mix value is {geometric}.
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See the "pair_modify" command for details.
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The "pair_modify"_pair_modify.html shift option is not relevant
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for these pair styles.
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The {coul/long} style supports the "pair_modify"_pair_modify.html
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table option for tabulation of the short-range portion of the
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long-range Coulombic interaction.
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These pair styles do not support the "pair_modify"_pair_modify.html
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tail option for adding long-range tail corrections to energy and
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pressure.
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These pair styles can calculate per-atom energy and stress, as used by
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the "compute epair/atom"_compute_epair_atom.html, "compute
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stress/atom"_compute_stress_atom.html, and "dump custom"_dump.html
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commands.
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These pair 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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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:]
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The {coul/long} style is part of the "kspace" package. It is only
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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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On some 64-bit machines, compiling with -O3 appears to break the
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Coulombic tabling option used by the {coul/long} style. See the
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"Additional build tips" section of the Making LAMMPS documentation
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pages for workarounds on this issue.
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[Related commands:]
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"pair_coeff"_pair_coeff.html, "pair_style
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hybrid/overlay"_pair_hybrid.html
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[Default:] none
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