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<div class="section" id="pair-style-lj-class2-command">
<span id="index-0"></span><h1>pair_style lj/class2 command</h1>
</div>
<div class="section" id="pair-style-lj-class2-gpu-command">
<h1>pair_style lj/class2/gpu command</h1>
</div>
<div class="section" id="pair-style-lj-class2-kk-command">
<h1>pair_style lj/class2/kk command</h1>
</div>
<div class="section" id="pair-style-lj-class2-omp-command">
<h1>pair_style lj/class2/omp command</h1>
</div>
<div class="section" id="pair-style-lj-class2-coul-cut-command">
<h1>pair_style lj/class2/coul/cut command</h1>
</div>
<div class="section" id="pair-style-lj-class2-coul-cut-kk-command">
<h1>pair_style lj/class2/coul/cut/kk command</h1>
</div>
<div class="section" id="pair-style-lj-class2-coul-cut-omp-command">
<h1>pair_style lj/class2/coul/cut/omp command</h1>
</div>
<div class="section" id="pair-style-lj-class2-coul-long-command">
<h1>pair_style lj/class2/coul/long command</h1>
</div>
<div class="section" id="pair-style-lj-class2-coul-long-gpu-command">
<h1>pair_style lj/class2/coul/long/gpu command</h1>
</div>
<div class="section" id="pair-style-lj-class2-coul-long-kk-command">
<h1>pair_style lj/class2/coul/long/kk command</h1>
</div>
<div class="section" id="pair-style-lj-class2-coul-long-omp-command">
<h1>pair_style lj/class2/coul/long/omp command</h1>
<div class="section" id="syntax">
<h2>Syntax</h2>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">pair_style</span> <span class="n">style</span> <span class="n">args</span>
</pre></div>
</div>
<ul class="simple">
<li>style = <em>lj/class2</em> or <em>lj/class2/coul/cut</em> or <em>lj/class2/coul/long</em></li>
<li>args = list of arguments for a particular style</li>
</ul>
<pre class="literal-block">
<em>lj/class2</em> args = cutoff
cutoff = global cutoff for class 2 interactions (distance units)
<em>lj/class2/coul/cut</em> args = cutoff (cutoff2)
cutoff = global cutoff for class 2 (and Coulombic if only 1 arg) (distance units)
cutoff2 = global cutoff for Coulombic (optional) (distance units)
<em>lj/class2/coul/long</em> args = cutoff (cutoff2)
cutoff = global cutoff for class 2 (and Coulombic if only 1 arg) (distance units)
cutoff2 = global cutoff for Coulombic (optional) (distance units)
</pre>
</div>
<div class="section" id="examples">
<h2>Examples</h2>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">pair_style</span> <span class="n">lj</span><span class="o">/</span><span class="n">class2</span> <span class="mf">10.0</span>
<span class="n">pair_coeff</span> <span class="o">*</span> <span class="o">*</span> <span class="mf">100.0</span> <span class="mf">2.5</span>
<span class="n">pair_coeff</span> <span class="mi">1</span> <span class="mi">2</span><span class="o">*</span> <span class="mf">100.0</span> <span class="mf">2.5</span> <span class="mf">9.0</span>
</pre></div>
</div>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">pair_style</span> <span class="n">lj</span><span class="o">/</span><span class="n">class2</span><span class="o">/</span><span class="n">coul</span><span class="o">/</span><span class="n">cut</span> <span class="mf">10.0</span>
<span class="n">pair_style</span> <span class="n">lj</span><span class="o">/</span><span class="n">class2</span><span class="o">/</span><span class="n">coul</span><span class="o">/</span><span class="n">cut</span> <span class="mf">10.0</span> <span class="mf">8.0</span>
<span class="n">pair_coeff</span> <span class="o">*</span> <span class="o">*</span> <span class="mf">100.0</span> <span class="mf">3.0</span>
<span class="n">pair_coeff</span> <span class="mi">1</span> <span class="mi">1</span> <span class="mf">100.0</span> <span class="mf">3.5</span> <span class="mf">9.0</span>
<span class="n">pair_coeff</span> <span class="mi">1</span> <span class="mi">1</span> <span class="mf">100.0</span> <span class="mf">3.5</span> <span class="mf">9.0</span> <span class="mf">9.0</span>
</pre></div>
</div>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">pair_style</span> <span class="n">lj</span><span class="o">/</span><span class="n">class2</span><span class="o">/</span><span class="n">coul</span><span class="o">/</span><span class="n">long</span> <span class="mf">10.0</span>
<span class="n">pair_style</span> <span class="n">lj</span><span class="o">/</span><span class="n">class2</span><span class="o">/</span><span class="n">coul</span><span class="o">/</span><span class="n">long</span> <span class="mf">10.0</span> <span class="mf">8.0</span>
<span class="n">pair_coeff</span> <span class="o">*</span> <span class="o">*</span> <span class="mf">100.0</span> <span class="mf">3.0</span>
<span class="n">pair_coeff</span> <span class="mi">1</span> <span class="mi">1</span> <span class="mf">100.0</span> <span class="mf">3.5</span> <span class="mf">9.0</span>
</pre></div>
</div>
</div>
<div class="section" id="description">
<h2>Description</h2>
<p>The <em>lj/class2</em> styles compute a 6/9 Lennard-Jones potential given by</p>
<img alt="_images/pair_class2.jpg" class="align-center" src="_images/pair_class2.jpg" />
<p>Rc is the cutoff.</p>
<p>The <em>lj/class2/coul/cut</em> and <em>lj/class2/coul/long</em> styles add a
Coulombic term as described for the <a class="reference internal" href="pair_lj.html"><span class="doc">lj/cut</span></a> pair styles.</p>
<p>See <a class="reference internal" href="#pair-sun"><span class="std std-ref">(Sun)</span></a> for a description of the COMPASS class2 force field.</p>
<p>The following coefficients must be defined for each pair of atoms
types via the <a class="reference internal" href="pair_coeff.html"><span class="doc">pair_coeff</span></a> command as in the examples
above, or in the data file or restart files read by the
<a class="reference internal" href="read_data.html"><span class="doc">read_data</span></a> or <a class="reference internal" href="read_restart.html"><span class="doc">read_restart</span></a>
commands, or by mixing as described below:</p>
<ul class="simple">
<li>epsilon (energy units)</li>
<li>sigma (distance units)</li>
<li>cutoff1 (distance units)</li>
<li>cutoff2 (distance units)</li>
</ul>
<p>The latter 2 coefficients are optional. If not specified, the global
class 2 and Coulombic cutoffs are used. If only one cutoff is
specified, it is used as the cutoff for both class 2 and Coulombic
interactions for this type pair. If both coefficients are specified,
they are used as the class 2 and Coulombic cutoffs for this type pair.
You cannot specify 2 cutoffs for style <em>lj/class2</em>, since it has no
Coulombic terms.</p>
<p>For <em>lj/class2/coul/long</em> only the class 2 cutoff can be specified
since a Coulombic cutoff cannot be specified for an individual I,J
type pair. All type pairs use the same global Coulombic cutoff
specified in the pair_style command.</p>
<hr class="docutils" />
<p>If the pair_coeff command is not used to define coefficients for a
particular I != J type pair, the mixing rule for epsilon and sigma for
all class2 potentials is to use the <em>sixthpower</em> formulas documented
by the <a class="reference internal" href="pair_modify.html"><span class="doc">pair_modify</span></a> command. The <a class="reference internal" href="pair_modify.html"><span class="doc">pair_modify mix</span></a> setting is thus ignored for class2 potentials
for epsilon and sigma. However it is still followed for mixing the
cutoff distance.</p>
<hr class="docutils" />
<p>Styles with a <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 <a class="reference internal" href="Section_accelerate.html"><span class="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 GPU, USER-INTEL, KOKKOS,
USER-OMP and OPT packages, respectively. They are only enabled if
LAMMPS was built with those packages. See the <a class="reference internal" href="Section_start.html#start-3"><span class="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 <a class="reference internal" href="Section_start.html#start-7"><span class="std std-ref">-suffix command-line switch</span></a> when you invoke LAMMPS, or you can
use the <a class="reference internal" href="suffix.html"><span class="doc">suffix</span></a> command in your input script.</p>
<p>See <a class="reference internal" href="Section_accelerate.html"><span class="doc">Section_accelerate</span></a> of the manual for
more instructions on how to use the accelerated styles effectively.</p>
<hr class="docutils" />
<p><strong>Mixing, shift, table, tail correction, restart, rRESPA info</strong>:</p>
<p>For atom type pairs I,J and I != J, the epsilon and sigma coefficients
and cutoff distance for all of the lj/class2 pair styles can be mixed.
Epsilon and sigma are always mixed with the value <em>sixthpower</em>. The
cutoff distance is mixed by whatever option is set by the pair_modify
command (default = geometric). See the &#8220;pair_modify&#8221; command for
details.</p>
<p>All of the lj/class2 pair styles support the
<a class="reference internal" href="pair_modify.html"><span class="doc">pair_modify</span></a> shift option for the energy of the
Lennard-Jones portion of the pair interaction.</p>
<p>The <em>lj/class2/coul/long</em> pair style does not support the
<a class="reference internal" href="pair_modify.html"><span class="doc">pair_modify</span></a> table option since a tabulation
capability has not yet been added to this potential.</p>
<p>All of the lj/class2 pair styles support the
<a class="reference internal" href="pair_modify.html"><span class="doc">pair_modify</span></a> tail option for adding a long-range
tail correction to the energy and pressure of the Lennard-Jones
portion of the pair interaction.</p>
<p>All of the lj/class2 pair styles write their information to <a class="reference internal" href="restart.html"><span class="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>All of the lj/class2 pair styles can only be used via the <em>pair</em>
keyword of the <a class="reference internal" href="run_style.html"><span class="doc">run_style respa</span></a> command. They do not
support the <em>inner</em>, <em>middle</em>, <em>outer</em> keywords.</p>
</div>
<div class="section" id="restrictions">
<h2>Restrictions</h2>
<p>These styles are part of the CLASS2 package. They are only enabled if
LAMMPS was built with that package. See the <a class="reference internal" href="Section_start.html#start-3"><span class="std std-ref">Making LAMMPS</span></a> section for more info.</p>
</div>
<div class="section" id="related-commands">
<h2>Related commands</h2>
<p><a class="reference internal" href="pair_coeff.html"><span class="doc">pair_coeff</span></a></p>
<p><strong>Default:</strong> none</p>
<hr class="docutils" />
<p id="pair-sun"><strong>(Sun)</strong> Sun, J Phys Chem B 102, 7338-7364 (1998).</p>
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