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<title>angle_style class2 command &mdash; LAMMPS 15 May 2015 version documentation</title>
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<div class="section" id="angle-style-class2-command">
<span id="index-0"></span><h1>angle_style class2 command<a class="headerlink" href="#angle-style-class2-command" title="Permalink to this headline"></a></h1>
</div>
<div class="section" id="angle-style-class2-omp-command">
<h1>angle_style class2/omp command<a class="headerlink" href="#angle-style-class2-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>angle_style class2
</pre></div>
</div>
</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>angle_style class2
angle_coeff * 75.0
angle_coeff 1 bb 10.5872 1.0119 1.5228
angle_coeff * ba 3.6551 24.895 1.0119 1.5228
</pre></div>
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<div class="section" id="description">
<h2>Description<a class="headerlink" href="#description" title="Permalink to this headline"></a></h2>
<p>The <em>class2</em> angle style uses the potential</p>
<img alt="_images/angle_class2.jpg" class="align-center" src="_images/angle_class2.jpg" />
<p>where Ea is the angle term, Ebb is a bond-bond term, and Eba is a
bond-angle term. Theta0 is the equilibrium angle and r1 and r2 are
the equilibrium bond lengths.</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>Coefficients for the Ea, Ebb, and Eba formulas must be defined for
each angle type via the <a class="reference internal" href="angle_coeff.html"><em>angle_coeff</em></a> command as in
the example 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.</p>
<p>These are the 4 coefficients for the Ea formula:</p>
<ul class="simple">
<li>theta0 (degrees)</li>
<li>K2 (energy/radian^2)</li>
<li>K3 (energy/radian^3)</li>
<li>K4 (energy/radian^4)</li>
</ul>
<p>Theta0 is specified in degrees, but LAMMPS converts it to radians
internally; hence the units of the various K are in per-radian.</p>
<p>For the Ebb formula, each line in a <a class="reference internal" href="angle_coeff.html"><em>angle_coeff</em></a>
command in the input script lists 4 coefficients, the first of which
is &#8220;bb&#8221; to indicate they are BondBond coefficients. In a data file,
these coefficients should be listed under a &#8220;BondBond Coeffs&#8221; heading
and you must leave out the &#8220;bb&#8221;, i.e. only list 3 coefficients after
the angle type.</p>
<ul class="simple">
<li>bb</li>
<li>M (energy/distance^2)</li>
<li>r1 (distance)</li>
<li>r2 (distance)</li>
</ul>
<p>For the Eba formula, each line in a <a class="reference internal" href="angle_coeff.html"><em>angle_coeff</em></a>
command in the input script lists 5 coefficients, the first of which
is &#8220;ba&#8221; to indicate they are BondAngle coefficients. In a data file,
these coefficients should be listed under a &#8220;BondAngle Coeffs&#8221; heading
and you must leave out the &#8220;ba&#8221;, i.e. only list 4 coefficients after
the angle type.</p>
<ul class="simple">
<li>ba</li>
<li>N1 (energy/distance^2)</li>
<li>N2 (energy/distance^2)</li>
<li>r1 (distance)</li>
<li>r2 (distance)</li>
</ul>
<p>The theta0 value in the Eba formula is not specified, since it is the
same value from the Ea formula.</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>
</div>
<hr class="docutils" />
<div class="section" id="restrictions">
<h2>Restrictions<a class="headerlink" href="#restrictions" title="Permalink to this headline"></a></h2>
<p>This angle style can only be used if LAMMPS was built with the CLASS2
package. See the <a class="reference internal" href="Section_start.html#start-3"><span>Making LAMMPS</span></a> section
for more info on packages.</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="angle_coeff.html"><em>angle_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>
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