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  <div class="section" id="pair-style-lj-class2-command">
<span id="index-0"></span><h1>pair_style lj/class2 command<a class="headerlink" href="#pair-style-lj-class2-command" title="Permalink to this headline">¶</a></h1>
</div>
<div class="section" id="pair-style-lj-class2-cuda-command">
<h1>pair_style lj/class2/cuda command<a class="headerlink" href="#pair-style-lj-class2-cuda-command" title="Permalink to this headline">¶</a></h1>
</div>
<div class="section" id="pair-style-lj-class2-gpu-command">
<h1>pair_style lj/class2/gpu command<a class="headerlink" href="#pair-style-lj-class2-gpu-command" title="Permalink to this headline">¶</a></h1>
</div>
<div class="section" id="pair-style-lj-class2-kk-command">
<h1>pair_style lj/class2/kk command<a class="headerlink" href="#pair-style-lj-class2-kk-command" title="Permalink to this headline">¶</a></h1>
</div>
<div class="section" id="pair-style-lj-class2-omp-command">
<h1>pair_style lj/class2/omp command<a class="headerlink" href="#pair-style-lj-class2-omp-command" title="Permalink to this headline">¶</a></h1>
</div>
<div class="section" id="pair-style-lj-class2-coul-cut-command">
<h1>pair_style lj/class2/coul/cut command<a class="headerlink" href="#pair-style-lj-class2-coul-cut-command" title="Permalink to this headline">¶</a></h1>
</div>
<div class="section" id="pair-style-lj-class2-coul-cut-cuda-command">
<h1>pair_style lj/class2/coul/cut/cuda command<a class="headerlink" href="#pair-style-lj-class2-coul-cut-cuda-command" title="Permalink to this headline">¶</a></h1>
</div>
<div class="section" id="pair-style-lj-class2-coul-cut-kk-command">
<h1>pair_style lj/class2/coul/cut/kk command<a class="headerlink" href="#pair-style-lj-class2-coul-cut-kk-command" title="Permalink to this headline">¶</a></h1>
</div>
<div class="section" id="pair-style-lj-class2-coul-cut-omp-command">
<h1>pair_style lj/class2/coul/cut/omp command<a class="headerlink" href="#pair-style-lj-class2-coul-cut-omp-command" title="Permalink to this headline">¶</a></h1>
</div>
<div class="section" id="pair-style-lj-class2-coul-long-command">
<h1>pair_style lj/class2/coul/long command<a class="headerlink" href="#pair-style-lj-class2-coul-long-command" title="Permalink to this headline">¶</a></h1>
</div>
<div class="section" id="pair-style-lj-class2-coul-long-cuda-command">
<h1>pair_style lj/class2/coul/long/cuda command<a class="headerlink" href="#pair-style-lj-class2-coul-long-cuda-command" title="Permalink to this headline">¶</a></h1>
</div>
<div class="section" id="pair-style-lj-class2-coul-long-gpu-command">
<h1>pair_style lj/class2/coul/long/gpu command<a class="headerlink" href="#pair-style-lj-class2-coul-long-gpu-command" title="Permalink to this headline">¶</a></h1>
</div>
<div class="section" id="pair-style-lj-class2-coul-long-kk-command">
<h1>pair_style lj/class2/coul/long/kk command<a class="headerlink" href="#pair-style-lj-class2-coul-long-kk-command" title="Permalink to this headline">¶</a></h1>
</div>
<div class="section" id="pair-style-lj-class2-coul-long-omp-command">
<h1>pair_style lj/class2/coul/long/omp command<a class="headerlink" href="#pair-style-lj-class2-coul-long-omp-command" title="Permalink to this headline">¶</a></h1>
<div class="section" id="syntax">
<h2>Syntax<a class="headerlink" href="#syntax" title="Permalink to this headline">¶</a></h2>
<div class="highlight-python"><div class="highlight"><pre>pair_style style args
</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<a class="headerlink" href="#examples" title="Permalink to this headline">¶</a></h2>
<div class="highlight-python"><div class="highlight"><pre>pair_style lj/class2 10.0
pair_coeff * * 100.0 2.5
pair_coeff 1 2* 100.0 2.5 9.0
</pre></div>
</div>
<div class="highlight-python"><div class="highlight"><pre>pair_style lj/class2/coul/cut 10.0
pair_style lj/class2/coul/cut 10.0 8.0
pair_coeff * * 100.0 3.0
pair_coeff 1 1 100.0 3.5 9.0
pair_coeff 1 1 100.0 3.5 9.0 9.0
</pre></div>
</div>
<div class="highlight-python"><div class="highlight"><pre>pair_style lj/class2/coul/long 10.0
pair_style lj/class2/coul/long 10.0 8.0
pair_coeff * * 100.0 3.0
pair_coeff 1 1 100.0 3.5 9.0
</pre></div>
</div>
</div>
<div class="section" id="description">
<h2>Description<a class="headerlink" href="#description" title="Permalink to this headline">¶</a></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"><em>lj/cut</em></a> pair styles.</p>
<p>See <a class="reference internal" href="pair_modify.html#sun"><span>(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"><em>pair_coeff</em></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"><em>read_data</em></a> or <a class="reference internal" href="read_restart.html"><em>read_restart</em></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"><em>pair_modify</em></a> command.  The <a class="reference internal" href="pair_modify.html"><em>pair_modify mix</em></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>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 <a class="reference internal" href="Section_accelerate.html"><em>Section_accelerate</em></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 <a class="reference internal" href="Section_start.html#start-3"><span>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>-suffix command-line switch</span></a> when you invoke LAMMPS, or you can
use the <a class="reference internal" href="suffix.html"><em>suffix</em></a> command in your input script.</p>
<p>See <a class="reference internal" href="Section_accelerate.html"><em>Section_accelerate</em></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"><em>pair_modify</em></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"><em>pair_modify</em></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"><em>pair_modify</em></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"><em>binary restart files</em></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"><em>run_style respa</em></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<a class="headerlink" href="#restrictions" title="Permalink to this headline">¶</a></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>Making LAMMPS</span></a> section for more info.</p>
</div>
<div class="section" id="related-commands">
<h2>Related commands<a class="headerlink" href="#related-commands" title="Permalink to this headline">¶</a></h2>
<p><a class="reference internal" href="pair_coeff.html"><em>pair_coeff</em></a></p>
<p><strong>Default:</strong> none</p>
<hr class="docutils" />
<p id="sun"><strong>(Sun)</strong> Sun, J Phys Chem B 102, 7338-7364 (1998).</p>
</div>
</div>


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