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<div class="section" id="pair-style-morse-command">
<span id="index-0"></span><h1>pair_style morse command</h1>
</div>
<div class="section" id="pair-style-morse-gpu-command">
<h1>pair_style morse/gpu command</h1>
</div>
<div class="section" id="pair-style-morse-omp-command">
<h1>pair_style morse/omp command</h1>
</div>
<div class="section" id="pair-style-morse-opt-command">
<h1>pair_style morse/opt command</h1>
</div>
<div class="section" id="pair-style-morse-smooth-linear-command">
<h1>pair_style morse/smooth/linear command</h1>
</div>
<div class="section" id="pair-style-morse-smooth-linear-omp-command">
<h1>pair_style morse/smooth/linear/omp command</h1>
</div>
<div class="section" id="pair-style-morse-soft-command">
<h1>pair_style morse/soft command</h1>
<div class="section" id="syntax">
<h2>Syntax</h2>
<pre class="literal-block">
pair_style style args
</pre>
<ul class="simple">
<li>style = <em>morse</em> or <em>morse/smooth/linear</em> or <em>morse/soft</em></li>
<li>args = list of arguments for a particular style</li>
</ul>
<pre class="literal-block">
<em>morse</em> args = cutoff
cutoff = global cutoff for Morse interactions (distance units)
<em>morse/smooth/linear</em> args = cutoff
cutoff = global cutoff for Morse interactions (distance units)
<em>morse/soft</em> args = n lf cutoff
n = soft-core parameter
lf = transformation range is lf &lt; lambda &lt; 1
cutoff = global cutoff for Morse interactions (distance units)
</pre>
</div>
<div class="section" id="examples">
<h2>Examples</h2>
<p>pair_style morse 2.5
pair_style morse/smooth/linear 2.5
pair_coeff * * 100.0 2.0 1.5
pair_coeff 1 1 100.0 2.0 1.5 3.0</p>
<pre class="literal-block">
pair_style morse/soft 4 0.9 10.0
pair_coeff * * 100.0 2.0 1.5 1.0
pair_coeff 1 1 100.0 2.0 1.5 1.0 3.0
</pre>
</div>
<div class="section" id="description">
<h2>Description</h2>
<p>Style <em>morse</em> computes pairwise interactions with the formula</p>
<img alt="_images/pair_morse.jpg" class="align-center" src="_images/pair_morse.jpg" />
<p>Rc is the cutoff.</p>
<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:</p>
<ul class="simple">
<li>D0 (energy units)</li>
<li>alpha (1/distance units)</li>
<li>r0 (distance units)</li>
<li>cutoff (distance units)</li>
</ul>
<p>The last coefficient is optional. If not specified, the global morse
cutoff is used.</p>
<hr class="docutils" />
<p>The <em>morse/smooth/linear</em> variant is similar to the lj/smooth/linear
variant in that it adds to the potential a shift and a linear term
so that both, potential energy and force, go to zero at the cut-off:</p>
<img alt="_images/pair_morse_smooth_linear.jpg" class="align-center" src="_images/pair_morse_smooth_linear.jpg" />
<p>The syntax of the pair_style and pair_coeff commands are the same for
the <em>morse</em> and <em>morse/smooth/linear</em> styles.</p>
<hr class="docutils" />
<p>The <em>morse/soft</em> variant is similar to the <em>lj/cut/soft</em> pair style
in that it modifies the potential at short range to have a soft core.
This helps to avoid singularities during free energy calculation in
which sites are created or anihilated. The formula differs from that
of <em>lj/cut/soft</em>, and is instead given by:</p>
<img alt="_images/pair_morse_soft.jpg" class="align-center" src="_images/pair_morse_soft.jpg" />
<p>The <em>morse/soft</em> style requires the following pair coefficients:</p>
<ul class="simple">
<li>D0 (energy units)</li>
<li>alpha (1/distance units)</li>
<li>r0 (distance units)</li>
<li>lamda (unitless, between 0.0 and 1.0)</li>
<li>cutoff (distance units)</li>
</ul>
<p>The last coefficient is optional. If not specified, the global morse
cutoff is 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>None of these pair styles support mixing. Thus, coefficients for all
I,J pairs must be specified explicitly.</p>
<p>All of these pair styles support 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 options is not relevant for
the Morse pair styles.</p>
<p>None of these pair styles 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.</p>
<p>All of these pair styles write their 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>These pair styles 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. They do 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>
<p>The <em>morse/smooth/linear</em> pair style is only enabled if LAMMPS was
built with the USER-MISC package. 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>The <em>morse/soft</em> pair style is only enabled if LAMMPS was built with
the USER-FEP package. 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>
</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></p>
<p><strong>Default:</strong> none</p>
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