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<div class="section" id="pair-style-lj-smooth-command">
<span id="index-0"></span><h1>pair_style lj/smooth command</h1>
</div>
<div class="section" id="pair-style-lj-smooth-omp-command">
<h1>pair_style lj/smooth/omp command</h1>
<div class="section" id="syntax">
<h2>Syntax</h2>
<pre class="literal-block">
pair_style lj/smooth Rin Rc
</pre>
<ul class="simple">
<li>Rin = inner cutoff beyond which force smoothing will be applied (distance units)</li>
<li>Rc = outer cutoff for lj/smooth interactions (distance units)</li>
</ul>
</div>
<div class="section" id="examples">
<h2>Examples</h2>
<pre class="literal-block">
pair_style lj/smooth 8.0 10.0
pair_coeff * * 10.0 1.5
pair_coeff 1 1 20.0 1.3 7.0 9.0
</pre>
</div>
<div class="section" id="description">
<h2>Description</h2>
<p>Style <em>lj/smooth</em> computes a LJ interaction with a force smoothing
applied between the inner and outer cutoff.</p>
<img alt="_images/pair_lj_smooth.jpg" class="align-center" src="_images/pair_lj_smooth.jpg" />
<p>The polynomial coefficients C1, C2, C3, C4 are computed by LAMMPS to
cause the force to vary smoothly from the inner cutoff Rin to the
outer cutoff Rc.</p>
<p>At the inner cutoff the force and its 1st derivative
will match the unsmoothed LJ formula. At the outer cutoff the force
and its 1st derivative will be 0.0. The inner cutoff cannot be 0.0.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">this force smoothing causes the energy to be discontinuous both
in its values and 1st derivative. This can lead to poor energy
conservation and may require the use of a thermostat. Plot the energy
and force resulting from this formula via the
<a class="reference internal" href="pair_write.html"><span class="doc">pair_write</span></a> command to see the effect.</p>
</div>
<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>innner (distance units)</li>
<li>outer (distance units)</li>
</ul>
<p>The last 2 coefficients are optional inner and outer cutoffs. If not
specified, the global values for Rin and Rc are used.</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, sigma, Rin
coefficients and the cutoff distance for this pair style can be mixed.
Rin is a cutoff value and is mixed like the cutoff. The other
coefficients are mixed according to the pair_modify mix option. The
default mix value is <em>geometric</em>. See the &#8220;pair_modify&#8221; command for
details.</p>
<p>This pair style supports the <a class="reference internal" href="pair_modify.html"><span class="doc">pair_modify</span></a> shift
option for the energy of the pair interaction.</p>
<p>The <a class="reference internal" href="pair_modify.html"><span class="doc">pair_modify</span></a> table option is not relevant
for this pair style.</p>
<p>This pair style does not support the <a class="reference internal" href="pair_modify.html"><span class="doc">pair_modify</span></a>
tail option for adding long-range tail corrections to energy and
pressure, since the energy of the pair interaction is smoothed to 0.0
at the cutoff.</p>
<p>This pair style writes its 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>This pair style 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. It does not support the
<em>inner</em>, <em>middle</em>, <em>outer</em> keywords.</p>
</div>
<hr class="docutils" />
<div class="section" id="restrictions">
<h2>Restrictions</h2>
<blockquote>
<div>none</div></blockquote>
</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>, <a class="reference internal" href="pair_lj_smooth_linear.html"><span class="doc">pair lj/smooth/linear</span></a></p>
<p><strong>Default:</strong> none</p>
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