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<div class="section" id="pair-style-buck-command">
<span id="index-0"></span><h1>pair_style buck command</h1>
</div>
<div class="section" id="pair-style-buck-gpu-command">
<h1>pair_style buck/gpu command</h1>
</div>
<div class="section" id="pair-style-buck-intel-command">
<h1>pair_style buck/intel command</h1>
</div>
<div class="section" id="pair-style-buck-kk-command">
<h1>pair_style buck/kk command</h1>
</div>
<div class="section" id="pair-style-buck-omp-command">
<h1>pair_style buck/omp command</h1>
</div>
<div class="section" id="pair-style-buck-coul-cut-command">
<h1>pair_style buck/coul/cut command</h1>
</div>
<div class="section" id="pair-style-buck-coul-cut-gpu-command">
<h1>pair_style buck/coul/cut/gpu command</h1>
</div>
<div class="section" id="pair-style-buck-coul-cut-intel-command">
<h1>pair_style buck/coul/cut/intel command</h1>
</div>
<div class="section" id="pair-style-buck-coul-cut-kk-command">
<h1>pair_style buck/coul/cut/kk command</h1>
</div>
<div class="section" id="pair-style-buck-coul-cut-omp-command">
<h1>pair_style buck/coul/cut/omp command</h1>
</div>
<div class="section" id="pair-style-buck-coul-long-command">
<h1>pair_style buck/coul/long command</h1>
</div>
<div class="section" id="pair-style-buck-coul-long-cs-command">
<h1>pair_style buck/coul/long/cs command</h1>
</div>
<div class="section" id="pair-style-buck-coul-long-gpu-command">
<h1>pair_style buck/coul/long/gpu command</h1>
</div>
<div class="section" id="pair-style-buck-coul-long-intel-command">
<h1>pair_style buck/coul/long/intel command</h1>
</div>
<div class="section" id="pair-style-buck-coul-long-kk-command">
<h1>pair_style buck/coul/long/kk command</h1>
</div>
<div class="section" id="pair-style-buck-coul-long-omp-command">
<h1>pair_style buck/coul/long/omp command</h1>
</div>
<div class="section" id="pair-style-buck-coul-msm-command">
<h1>pair_style buck/coul/msm command</h1>
</div>
<div class="section" id="pair-style-buck-coul-msm-omp-command">
<h1>pair_style buck/coul/msm/omp command</h1>
<div class="section" id="syntax">
<h2>Syntax</h2>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">pair_style</span> <span class="n">style</span> <span class="n">args</span>
</pre></div>
</div>
<ul class="simple">
<li>style = <em>buck</em> or <em>buck/coul/cut</em> or <em>buck/coul/long</em> or <em>buck/coul/long/cs</em> or <em>buck/coul/msm</em></li>
<li>args = list of arguments for a particular style</li>
</ul>
<pre class="literal-block">
<em>buck</em> args = cutoff
cutoff = global cutoff for Buckingham interactions (distance units)
<em>buck/coul/cut</em> args = cutoff (cutoff2)
cutoff = global cutoff for Buckingham (and Coulombic if only 1 arg) (distance units)
cutoff2 = global cutoff for Coulombic (optional) (distance units)
<em>buck/coul/long</em> or <em>buck/coul/long/cs</em> args = cutoff (cutoff2)
cutoff = global cutoff for Buckingham (and Coulombic if only 1 arg) (distance units)
cutoff2 = global cutoff for Coulombic (optional) (distance units)
<em>buck/coul/msm</em> args = cutoff (cutoff2)
cutoff = global cutoff for Buckingham (and Coulombic if only 1 arg) (distance units)
cutoff2 = global cutoff for Coulombic (optional) (distance units)
</pre>
</div>
<div class="section" id="examples">
<h2>Examples</h2>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">pair_style</span> <span class="n">buck</span> <span class="mf">2.5</span>
<span class="n">pair_coeff</span> <span class="o">*</span> <span class="o">*</span> <span class="mf">100.0</span> <span class="mf">1.5</span> <span class="mf">200.0</span>
<span class="n">pair_coeff</span> <span class="o">*</span> <span class="o">*</span> <span class="mf">100.0</span> <span class="mf">1.5</span> <span class="mf">200.0</span> <span class="mf">3.0</span>
</pre></div>
</div>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">pair_style</span> <span class="n">buck</span><span class="o">/</span><span class="n">coul</span><span class="o">/</span><span class="n">cut</span> <span class="mf">10.0</span>
<span class="n">pair_style</span> <span class="n">buck</span><span class="o">/</span><span class="n">coul</span><span class="o">/</span><span class="n">cut</span> <span class="mf">10.0</span> <span class="mf">8.0</span>
<span class="n">pair_coeff</span> <span class="o">*</span> <span class="o">*</span> <span class="mf">100.0</span> <span class="mf">1.5</span> <span class="mf">200.0</span>
<span class="n">pair_coeff</span> <span class="mi">1</span> <span class="mi">1</span> <span class="mf">100.0</span> <span class="mf">1.5</span> <span class="mf">200.0</span> <span class="mf">9.0</span>
<span class="n">pair_coeff</span> <span class="mi">1</span> <span class="mi">1</span> <span class="mf">100.0</span> <span class="mf">1.5</span> <span class="mf">200.0</span> <span class="mf">9.0</span> <span class="mf">8.0</span>
</pre></div>
</div>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">pair_style</span> <span class="n">buck</span><span class="o">/</span><span class="n">coul</span><span class="o">/</span><span class="n">long</span> <span class="mf">10.0</span>
<span class="n">pair_style</span> <span class="n">buck</span><span class="o">/</span><span class="n">coul</span><span class="o">/</span><span class="n">long</span><span class="o">/</span><span class="n">cs</span> <span class="mf">10.0</span>
<span class="n">pair_style</span> <span class="n">buck</span><span class="o">/</span><span class="n">coul</span><span class="o">/</span><span class="n">long</span> <span class="mf">10.0</span> <span class="mf">8.0</span>
<span class="n">pair_style</span> <span class="n">buck</span><span class="o">/</span><span class="n">coul</span><span class="o">/</span><span class="n">long</span><span class="o">/</span><span class="n">cs</span> <span class="mf">10.0</span> <span class="mf">8.0</span>
<span class="n">pair_coeff</span> <span class="o">*</span> <span class="o">*</span> <span class="mf">100.0</span> <span class="mf">1.5</span> <span class="mf">200.0</span>
<span class="n">pair_coeff</span> <span class="mi">1</span> <span class="mi">1</span> <span class="mf">100.0</span> <span class="mf">1.5</span> <span class="mf">200.0</span> <span class="mf">9.0</span>
</pre></div>
</div>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">pair_style</span> <span class="n">buck</span><span class="o">/</span><span class="n">coul</span><span class="o">/</span><span class="n">msm</span> <span class="mf">10.0</span>
<span class="n">pair_style</span> <span class="n">buck</span><span class="o">/</span><span class="n">coul</span><span class="o">/</span><span class="n">msm</span> <span class="mf">10.0</span> <span class="mf">8.0</span>
<span class="n">pair_coeff</span> <span class="o">*</span> <span class="o">*</span> <span class="mf">100.0</span> <span class="mf">1.5</span> <span class="mf">200.0</span>
<span class="n">pair_coeff</span> <span class="mi">1</span> <span class="mi">1</span> <span class="mf">100.0</span> <span class="mf">1.5</span> <span class="mf">200.0</span> <span class="mf">9.0</span>
</pre></div>
</div>
</div>
<div class="section" id="description">
<h2>Description</h2>
<p>The <em>buck</em> style computes a Buckingham potential (exp/6 instead of
Lennard-Jones 12/6) given by</p>
<img alt="_images/pair_buck.jpg" class="align-center" src="_images/pair_buck.jpg" />
<p>where rho is an ionic-pair dependent length parameter, and Rc is the
cutoff on both terms.</p>
<p>The styles with <em>coul/cut</em> or <em>coul/long</em> or <em>coul/msm</em> add a
Coulombic term as described for the <a class="reference internal" href="pair_lj.html"><span class="doc">lj/cut</span></a> pair styles.
For <em>buck/coul/long</em> and <em>buc/coul/msm</em>, an additional damping factor
is applied to the Coulombic term so it can be used in conjunction with
the <a class="reference internal" href="kspace_style.html"><span class="doc">kspace_style</span></a> command and its <em>ewald</em> or <em>pppm</em>
or <em>msm</em> option. The Coulombic cutoff specified for this style means
that pairwise interactions within this distance are computed directly;
interactions outside that distance are computed in reciprocal space.</p>
<p>If one cutoff is specified for the <em>born/coul/cut</em> and
<em>born/coul/long</em> and <em>born/coul/msm</em> styles, it is used for both the
A,C and Coulombic terms. If two cutoffs are specified, the first is
used as the cutoff for the A,C terms, and the second is the cutoff for
the Coulombic term.</p>
<p>Style <em>buck/coul/long/cs</em> is identical to <em>buck/coul/long</em> except that
a term is added for the <a class="reference internal" href="Section_howto.html#howto-25"><span class="std std-ref">core/shell model</span></a>
to allow charges on core and shell particles to be separated by r =
0.0.</p>
<p>Note that these potentials are related to the <a class="reference internal" href="pair_born.html"><span class="doc">Born-Mayer-Huggins potential</span></a>.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">For all these pair styles, the terms with A and C are always
cutoff. The additional Coulombic term can be cutoff or long-range (no
cutoff) depending on whether the style name includes coul/cut or
coul/long or coul/msm. If you wish the C/r^6 term to be long-range
(no cutoff), then see the <a class="reference internal" href="pair_buck_long.html"><span class="doc">pair_style buck/long/coul/long</span></a> command.</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:</p>
<ul class="simple">
<li>A (energy units)</li>
<li>rho (distance units)</li>
<li>C (energy-distance^6 units)</li>
<li>cutoff (distance units)</li>
<li>cutoff2 (distance units)</li>
</ul>
<p>The second coefficient, rho, must be greater than zero.</p>
<p>The latter 2 coefficients are optional. If not specified, the global
A,C and Coulombic cutoffs are used. If only one cutoff is specified,
it is used as the cutoff for both A,C and Coulombic interactions for
this type pair. If both coefficients are specified, they are used as
the A,C and Coulombic cutoffs for this type pair. You cannot specify
2 cutoffs for style <em>buck</em>, since it has no Coulombic terms.</p>
<p>For <em>buck/coul/long</em> only the LJ cutoff can be specified since a
Coulombic cutoff cannot be specified for an individual I,J type pair.
All type pairs use the same global Coulombic cutoff specified in the
pair_style command.</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>These pair styles do not support mixing. Thus, coefficients for all
I,J pairs must be specified explicitly.</p>
<p>These 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 exp() and 1/r^6 portion of the pair interaction.</p>
<p>The <em>buck/coul/long</em> pair style supports the
<a class="reference internal" href="pair_modify.html"><span class="doc">pair_modify</span></a> table option to tabulate the
short-range portion of the long-range Coulombic interaction.</p>
<p>These styles support the pair_modify tail option for adding long-range
tail corrections to energy and pressure for the A,C terms in the
pair interaction.</p>
<p>These 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 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>
<div class="section" id="restrictions">
<h2>Restrictions</h2>
<p>The <em>buck/coul/long</em> style is part of the KSPACE package. The
<em>buck/coul/long/cs</em> style is part of the CORESHELL package. They are
only enabled if LAMMPS was built with that 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.</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>, <a class="reference internal" href="pair_born.html"><span class="doc">pair_style born</span></a></p>
<p><strong>Default:</strong> none</p>
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