<p>to define a finite extensible nonlinear elastic (FENE) potential
<aclass="reference internal"href="#feneexpand-kremer"><spanclass="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
<aclass="reference internal"href="bond_coeff.html"><spanclass="doc">bond_coeff</span></a> command as in the example 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:</p>
<ulclass="simple">
<li>K (energy/distance^2)</li>
<li>R0 (distance)</li>
<li>epsilon (energy)</li>
<li>sigma (distance)</li>
<li>delta (distance)</li>
</ul>
<hrclass="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 <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 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>
</div>
<hrclass="docutils"/>
<divclass="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 <aclass="reference internal"href="Section_start.html#start-3"><spanclass="std std-ref">Making LAMMPS</span></a> section for more info on packages.</p>
<p>You typically should specify <aclass="reference external"href="special_bonds.html"">special_bonds fene</a>
or <aclass="reference internal"href="special_bonds.html"><spanclass="doc">special_bonds lj/coul 0 1 1</span></a> to use this bond
style. LAMMPS will issue a warning it that’s not the case.</p>
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