forked from lijiext/lammps
100 lines
3.1 KiB
Plaintext
100 lines
3.1 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 lj/smooth command :h3
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[Syntax:]
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pair_style lj/smooth Rin cutoff :pre
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Rin = global inner cutoff beyond which force smoothing will be applied (distance units)
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cutoff = global cutoff for lj/smooth interactions (distance units) :ul
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[Examples:]
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pair_style lj/smooth 8.0 10.0
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pair_coeff * * 10.0 1.5
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pair_coeff 1 1 20.0 1.3 7.0 9.0 :pre
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[Description:]
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Style {lj/smooth} computes a LJ interaction with a force smoothing
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applied between the inner and outer cutoff.
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:c,image(Eqs/pair_lj_smooth.jpg)
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The polynomial coefficients C1, C2, C3, C4 are computed by LAMMPS to
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cause the force to vary smoothly from Rin to Rc. At Rin the force and
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its 1st derivative will match the unsmoothed LJ formula. At Rc the
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force and its 1st derivative will be 0.0.
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IMPORTANT NOTE: this force smoothing causes the energy to be
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discontinuous both in its values and 1st derivative. This can lead to
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poor energy conservation and may require the use of a thermostat.
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Plot the energy and force resulting from this formula via the
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"pair_write"_pair_write.html command to see the effect.
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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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epsilon (energy units)
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sigma (distance units)
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Rin (distance units)
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cutoff (distance units) :ul
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The last 2 coefficients are optional. If not specified, the global
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Rin and cutoff are used. Rin cannot be 0.0. If Rin = cutoff, then no
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force smoothing is performed for this type pair; the standard LJ
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formula is used.
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:line
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[Mixing, shift, table, tail correction, per-atom energy/stress, and
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restart info]:
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For atom type pairs I,J and I != J, the epsilon, sigma, Rin
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coefficients and the cutoff distance for this pair style can be mixed.
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Rin is a cutoff value and is mixed like the cutoff. The other
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coefficients are mixed according to the pair_modify mix option. The
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default mix value is {geometric}. See the "pair_modify" command for
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details.
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This pair style supports the "pair_modify"_pair_modify.html shift
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option for the energy of the pair interaction.
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The "pair_modify"_pair_modify.html table option is not relevant
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for this pair style.
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This pair style does 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, since the energy of the pair interaction is smoothed to 0.0
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at the cutoff.
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This pair style 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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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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:line
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[Restrictions:] none
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[Related commands:]
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"pair_coeff"_pair_coeff.html
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[Default:] none
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