lammps/doc/pair_lj_smooth.txt

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:link(ld,Manual.html)
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pair_style lj/smooth command :h3

[Syntax:]

pair_style lj/smooth Rin cutoff :pre

Rin = global inner cutoff beyond which force smoothing will be applied (distance units)
cutoff = global cutoff for lj/smooth interactions (distance units) :ul

[Examples:]

pair_style lj/smooth 8.0 10.0
pair_coeff * * 10.0 1.5
pair_coeff 1 1 20.0 1.3 7.0 9.0 :pre

[Description:]

Style {lj/smooth} computes a LJ interaction with a force smoothing
applied between the inner and outer cutoff.

:c,image(Eqs/pair_lj_smooth.jpg)

The polynomial coefficients C1, C2, C3, C4 are computed by LAMMPS to
cause the force to vary smoothly from Rin to Rc.  At Rin the force and
its 1st derivative will match the unsmoothed LJ formula.  At Rc the
force and its 1st derivative will be 0.0.

IMPORTANT NOTE: this force smoothing causes the energy to be
discontinuous both in its values and 1st derivative.  This can lead to
poor energy conservation and may require the use of a thermostat.
Plot the energy and force resulting from this formula via the
"pair_write"_pair_write.html command to see the effect.

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:

epsilon (energy units)
sigma (distance units)
Rin (distance units)
cutoff (distance units) :ul

The last 2 coefficients are optional.  If not specified, the global
Rin and cutoff are used.  Rin cannot be 0.0.  If Rin = cutoff, then no
force smoothing is performed for this type pair; the standard LJ
formula is used.

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[Mixing, shift, table, tail correction, per-atom energy/stress, and
restart info]:

For atom type pairs I,J and I != J, the epsilon, sigma, Rin
coefficients and the cutoff distance for this pair style can be mixed.
Rin is a cutoff value and is mixed like the cutoff.  The other
coefficients are mixed according to the pair_modify mix option.  The
default mix value is {geometric}.  See the "pair_modify" command for
details.

This pair style supports the "pair_modify"_pair_modify.html shift
option for the energy of the pair interaction.

The "pair_modify"_pair_modify.html table option is not relevant
for this pair style.

This pair style does not support the "pair_modify"_pair_modify.html
tail option for adding long-range tail corrections to energy and
pressure, since the energy of the pair interaction is smoothed to 0.0
at the cutoff.

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.

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[Restrictions:] none

[Related commands:]

"pair_coeff"_pair_coeff.html

[Default:] none