lammps/doc/pair_lj_smooth.txt

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

[Syntax:]

pair_style lj/smooth Rin Rc :pre

Rin = inner cutoff beyond which force smoothing will be applied (distance units)
Rc = outer 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 the inner cutoff Rin to the
outer cutoff Rc. 

At the inner cutoff the force and its 1st derivative
will match the unsmoothed LJ formula.  At the outer cutoff the force
and its 1st derivative will be 0.0.  The inner cutoff cannot 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)
innner (distance units)
outer (distance units) :ul

The last 2 coefficients are optional inner and outer cutoffs.  If not
specified, the global values for Rin and Rc are used.

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Styles with a {cuda}, {gpu}, or {opt} suffix are functionally the same
as the corresponding style without the suffix.  They have been
optimized to run faster, depending on your available hardware, as
discussed in "this section"_Section_accelerate.html of the manual.
The accelerated styles take the same arguments and should produce the
same results, except for round-off and precision issues.

These accelerated styles are part of the "user-cuda", "gpu", and "opt"
packages respectively.  They are only enabled if LAMMPS was built with
those packages.  See the "Making LAMMPS"_Section_start.html#2_3
section for more info.

You can specify the accelerated styles explicitly in your input script
by including their suffix, or you can use the "-suffix command-line
switch"_Section_start.html#2_6 when you invoke LAMMPS, or you can use
the "suffix"_suffix.html command in your input script.

See "this section"_Section_accelerate.html of the manual for more
instructions on how to use the accelerated styles effectively.

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[Mixing, shift, table, tail correction, restart, rRESPA 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 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.

This pair style can only be used via the {pair} keyword of the
"run_style respa"_run_style.html command.  It does not support the
{inner}, {middle}, {outer} keywords.

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[Restrictions:] none

[Related commands:]

"pair_coeff"_pair_coeff.html

[Default:] none