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<div class="section" id="bond-style-fene-expand-command">
<span id="index-0"></span><h1>bond_style fene/expand command</h1>
</div>
<div class="section" id="bond-style-fene-expand-omp-command">
<h1>bond_style fene/expand/omp command</h1>
<div class="section" id="syntax">
<h2>Syntax</h2>
<pre class="literal-block">
bond_style fene/expand
</pre>
</div>
<div class="section" id="examples">
<h2>Examples</h2>
<pre class="literal-block">
bond_style fene/expand
bond_coeff 1 30.0 1.5 1.0 1.0 0.5
</pre>
</div>
<div class="section" id="description">
<h2>Description</h2>
<p>The <em>fene/expand</em> bond style uses the potential</p>
<img alt="_images/bond_fene_expand.jpg" class="align-center" src="_images/bond_fene_expand.jpg" />
<p>to define a finite extensible nonlinear elastic (FENE) potential
<a class="reference internal" href="#feneexpand-kremer"><span class="std std-ref">(Kremer)</span></a>, used for bead-spring polymer models. The first
term is attractive, the 2nd Lennard-Jones term is repulsive.</p>
<p>The <em>fene/expand</em> bond style is similar to <em>fene</em> except that an extra
shift factor of delta (positive or negative) is added to <em>r</em> to
effectively change the bead size of the bonded atoms. The first term
now extends to R0 + delta and the 2nd term is cutoff at 2^(1/6) sigma
+ delta.</p>
<p>The following coefficients must be defined for each bond type via the
<a class="reference internal" href="bond_coeff.html"><span class="doc">bond_coeff</span></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"><span class="doc">read_data</span></a>
or <a class="reference internal" href="read_restart.html"><span class="doc">read_restart</span></a> commands:</p>
<ul class="simple">
<li>K (energy/distance^2)</li>
<li>R0 (distance)</li>
<li>epsilon (energy)</li>
<li>sigma (distance)</li>
<li>delta (distance)</li>
</ul>
<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 5</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 5</span></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</h2>
<p>This bond style can only be used if LAMMPS was built with the
MOLECULE package (which it is by default). 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 on packages.</p>
<p>You typically should specify <a class="reference external" href="special_bonds.html&quot;">special_bonds fene</a>
or <a class="reference internal" href="special_bonds.html"><span class="doc">special_bonds lj/coul 0 1 1</span></a> to use this bond
style. LAMMPS will issue a warning it that&#8217;s not the case.</p>
</div>
<div class="section" id="related-commands">
<h2>Related commands</h2>
<p><a class="reference internal" href="bond_coeff.html"><span class="doc">bond_coeff</span></a>, <a class="reference internal" href="delete_bonds.html"><span class="doc">delete_bonds</span></a></p>
<p><strong>Default:</strong> none</p>
<hr class="docutils" />
<p id="feneexpand-kremer"><strong>(Kremer)</strong> Kremer, Grest, J Chem Phys, 92, 5057 (1990).</p>
</div>
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