<li>style = <em>lj/charmm/coul/charmm</em> or <em>lj/charmm/coul/charmm/implicit</em> or <em>lj/charmm/coul/long</em> or <em>lj/charmm/coul/msm</em></li>
<li>args = list of arguments for a particular style</li>
<p>The <em>lj/charmm</em> styles compute LJ and Coulombic interactions with an
additional switching function S(r) that ramps the energy and force
smoothly to zero between an inner and outer cutoff. It is a widely
used potential in the <aclass="reference external"href="http://www.scripps.edu/brooks">CHARMM</a> MD code.
See <aclass="reference internal"href="special_bonds.html#mackerell"><spanclass="std std-ref">(MacKerell)</span></a> for a description of the CHARMM force
<p>Both the LJ and Coulombic terms require an inner and outer cutoff.
They can be the same for both formulas or different depending on
whether 2 or 4 arguments are used in the pair_style command. In each
case, the inner cutoff distance must be less than the outer cutoff.
It it typical to make the difference between the 2 cutoffs about 1.0
Angstrom.</p>
<p>Style <em>lj/charmm/coul/charmm/implicit</em> computes the same formulas as
style <em>lj/charmm/coul/charmm</em> except that an additional 1/r term is
included in the Coulombic formula. The Coulombic energy thus varies
as 1/r^2. This is effectively a distance-dependent dielectric term
which is a simple model for an implicit solvent with additional
screening. It is designed for use in a simulation of an unsolvated
biomolecule (no explicit water molecules).</p>
<p>Styles <em>lj/charmm/coul/long</em> and <em>lj/charmm/coul/msm</em> compute the same
formulas as style <em>lj/charmm/coul/charmm</em> except that an additional
damping factor is applied to the Coulombic term, as described for the
<aclass="reference internal"href="pair_lj.html"><spanclass="doc">lj/cut</span></a> pair styles. Only one Coulombic cutoff is
specified for <em>lj/charmm/coul/long</em> and <em>lj/charmm/coul/msm</em>; if only
2 arguments are used in the pair_style command, then the outer LJ
cutoff is used as the single Coulombic cutoff.</p>
<p>The following coefficients must be defined for each pair of atoms
types via the <aclass="reference internal"href="pair_coeff.html"><spanclass="doc">pair_coeff</span></a> command as in the examples
above, or in the data file or restart files read by the
<aclass="reference internal"href="read_data.html"><spanclass="doc">read_data</span></a> or <aclass="reference internal"href="read_restart.html"><spanclass="doc">read_restart</span></a>
commands, or by mixing as described below:</p>
<ulclass="simple">
<li>epsilon (energy units)</li>
<li>sigma (distance units)</li>
<li>epsilon_14 (energy units)</li>
<li>sigma_14 (distance units)</li>
</ul>
<p>Note that sigma is defined in the LJ formula as the zero-crossing
distance for the potential, not as the energy minimum at 2^(1/6)
sigma.</p>
<p>The latter 2 coefficients are optional. If they are specified, they
are used in the LJ formula between 2 atoms of these types which are
also first and fourth atoms in any dihedral. No cutoffs are specified
because this CHARMM force field does not allow varying cutoffs for
individual atom pairs; all pairs use the global cutoff(s) specified in
the pair_style command.</p>
<hrclass="docutils"/>
<p>Styles with a <em>cuda</em>, <em>gpu</em>, <em>intel</em>, <em>kk</em>, <em>omp</em>, or <em>opt</em> 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 <aclass="reference internal"href="Section_accelerate.html"><spanclass="doc">Section_accelerate</span></a>
of the manual. The accelerated styles take the same arguments and
should produce the same results, except for round-off and precision
issues.</p>
<p>These accelerated styles are part of the USER-CUDA, GPU, USER-INTEL,
KOKKOS, USER-OMP and OPT packages, respectively. They are only
enabled if LAMMPS was built with those packages. See the <aclass="reference internal"href="Section_start.html#start-3"><spanclass="std std-ref">Making LAMMPS</span></a> section for more info.</p>
<p>You can specify the accelerated styles explicitly in your input script
by including their suffix, or you can use the <aclass="reference internal"href="Section_start.html#start-7"><spanclass="std std-ref">-suffix command-line switch</span></a> when you invoke LAMMPS, or you can
use the <aclass="reference internal"href="suffix.html"><spanclass="doc">suffix</span></a> command in your input script.</p>
<p>See <aclass="reference internal"href="Section_accelerate.html"><spanclass="doc">Section_accelerate</span></a> of the manual for
more instructions on how to use the accelerated styles effectively.</p>
<p>For atom type pairs I,J and I != J, the epsilon, sigma, epsilon_14,
and sigma_14 coefficients for all of the lj/charmm pair styles can be
mixed. The default mix value is <em>arithmetic</em> to coincide with the
usual settings for the CHARMM force field. See the “pair_modify”
command for details.</p>
<p>None of the lj/charmm pair styles support the
<aclass="reference internal"href="pair_modify.html"><spanclass="doc">pair_modify</span></a> shift option, since the Lennard-Jones
portion of the pair interaction is smoothed to 0.0 at the cutoff.</p>
<p>The <em>lj/charmm/coul/long</em> style supports the
<aclass="reference internal"href="pair_modify.html"><spanclass="doc">pair_modify</span></a> table option since it can tabulate the
short-range portion of the long-range Coulombic interaction.</p>
<p>None of the lj/charmm pair styles support the
<aclass="reference internal"href="pair_modify.html"><spanclass="doc">pair_modify</span></a> tail option for adding long-range tail
corrections to energy and pressure, since the Lennard-Jones portion of
the pair interaction is smoothed to 0.0 at the cutoff.</p>
<p>All of the lj/charmm pair styles write their information to <aclass="reference internal"href="restart.html"><spanclass="doc">binary restart files</span></a>, so pair_style and pair_coeff commands do
not need to be specified in an input script that reads a restart file.</p>
<p>The lj/charmm/coul/long pair style supports the use of the <em>inner</em>,
<em>middle</em>, and <em>outer</em> keywords of the <aclass="reference internal"href="run_style.html"><spanclass="doc">run_style respa</span></a>
command, meaning the pairwise forces can be partitioned by distance at
different levels of the rRESPA hierarchy. The other styles only
support the <em>pair</em> keyword of run_style respa. See the
<aclass="reference internal"href="run_style.html"><spanclass="doc">run_style</span></a> command for details.</p>
</div>
<hrclass="docutils"/>
<divclass="section"id="restrictions">
<h2>Restrictions</h2>
<p>The <em>lj/charmm/coul/charmm</em> and <em>lj/charmm/coul/charmm/implicit</em>
styles are part of the MOLECULE package. The <em>lj/charmm/coul/long</em>
style is part of the KSPACE package. They are only enabled if LAMMPS
was built with those packages. See the <aclass="reference internal"href="Section_start.html#start-3"><spanclass="std std-ref">Making LAMMPS</span></a> section for more info. Note that
the MOLECULE and KSPACE packages are installed by default.</p>
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