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<div class="section" id="pair-style-lj-mdf-command">
<span id="index-0"></span><h1>pair_style lj/mdf command<a class="headerlink" href="#pair-style-lj-mdf-command" title="Permalink to this headline">¶</a></h1>
</div>
<div class="section" id="pair-style-buck-mdf-command">
<h1>pair_style buck/mdf command<a class="headerlink" href="#pair-style-buck-mdf-command" title="Permalink to this headline">¶</a></h1>
</div>
<div class="section" id="pair-style-lennard-mdf-command">
<h1>pair_style lennard/mdf command<a class="headerlink" href="#pair-style-lennard-mdf-command" title="Permalink to this headline">¶</a></h1>
<div class="section" id="syntax">
<h2>Syntax<a class="headerlink" href="#syntax" title="Permalink to this headline">¶</a></h2>
<div class="highlight-python"><div class="highlight"><pre>pair_style style args
</pre></div>
</div>
<ul class="simple">
<li>style = <em>lj/mdf</em> or <em>buck/mdf</em> or <em>lennard/mdf</em></li>
<li>args = list of arguments for a particular style</li>
</ul>
<pre class="literal-block">
<em>lj/mdf</em> args = cutoff1 cutoff2
cutoff1 = inner cutoff for the start of the tapering function
cutoff1 = out cutoff for the end of the tapering function
<em>buck/mdf</em> args = cutoff1 cutoff2
cutoff1 = inner cutoff for the start of the tapering function
cutoff1 = out cutoff for the end of the tapering function
<em>lennard/mdf</em> args = cutoff1 cutoff2
cutoff1 = inner cutoff for the start of the tapering function
cutoff1 = out cutoff for the end of the tapering function
</pre>
</div>
<div class="section" id="examples">
<h2>Examples<a class="headerlink" href="#examples" title="Permalink to this headline">¶</a></h2>
<div class="highlight-python"><div class="highlight"><pre>pair_style lj/mdf 2.5 3.0
pair_coeff * * 1 1
pair_coeff 1 1 1 1.1 2.8 3.0 3.2
</pre></div>
</div>
<div class="highlight-python"><div class="highlight"><pre>pair_style buck 2.5 3.0
pair_coeff * * 100.0 1.5 200.0
pair_coeff * * 100.0 1.5 200.0 3.0 3.5
</pre></div>
</div>
<div class="highlight-python"><div class="highlight"><pre>pair_style lennard/mdf 2.5 3.0
pair_coeff * * 1 1
pair_coeff 1 1 1 1.1 2.8 3.0 3.2
</pre></div>
</div>
</div>
<div class="section" id="description">
<h2>Description<a class="headerlink" href="#description" title="Permalink to this headline">¶</a></h2>
<p>The <em>lj/mdf</em>, <em>buck/mdf</em> and <em>lennard/mdf</em> compute the standard 12-6
Lennard-Jones and Buckingham potential with the addition of a taper
function that ramps the energy and force smoothly to zero between an
inner and outer cutoff.</p>
<img alt="Eqs/pair_mdf-1.jpg" class="align-center" src="Eqs/pair_mdf-1.jpg" />
<p>The tapering, <em>f(r)</em>, is done by using the Mei, Davenport, Fernando
function <a class="reference internal" href="#mei"><span>(Mei)</span></a>.</p>
<img alt="Eqs/pair_mdf-2.jpg" class="align-center" src="Eqs/pair_mdf-2.jpg" />
<p>where</p>
<img alt="Eqs/pair_mdf-3.jpg" class="align-center" src="Eqs/pair_mdf-3.jpg" />
<p>Here <em>r_m</em> is the inner cutoff radius and <em>r_cut</em> is the outer cutoff
radius.</p>
<hr class="docutils" />
<p>For the <em>lj/mdf</em> pair_style, the potential energy, <em>E(r)</em>, is the
standard 12-6 Lennard-Jones written in the epsilon/sigma form:</p>
<img alt="Eqs/pair_mdf-4.jpg" class="align-center" src="Eqs/pair_mdf-4.jpg" />
<p>The following coefficients must be defined for each pair of atoms
types via the pair_coeff 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"><em>read_data</em></a> or
<a class="reference internal" href="read_restart.html"><em>read_restart commands</em></a>, or by mixing as described
below:</p>
<ul class="simple">
<li>epsilon (energy units)</li>
<li>sigma (distance units)</li>
<li>r_m (distance units)</li>
<li>r_*cut* (distance units)</li>
</ul>
<hr class="docutils" />
<p>For the <em>buck/mdf</em> pair_style, the potential energy, <em>E(r)</em>, is the
standard 12-6 Lennard-Jones written in the epsilon/sigma form:</p>
<img alt="Eqs/pair_mdf-5.jpg" class="align-center" src="Eqs/pair_mdf-5.jpg" />
<ul class="simple">
<li>A (energy units)</li>
<li>rho (distance units)</li>
<li>C (energy-distance^6 units)</li>
<li>r_m (distance units)</li>
<li>r_*cut*$ (distance units)</li>
</ul>
<hr class="docutils" />
<p>For the <em>lennard/mdf</em> pair_style, the potential energy, <em>E(r)</em>, is the
standard 12-6 Lennard-Jones written in the $A/B$ form:</p>
<img alt="Eqs/pair_mdf-6.jpg" class="align-center" src="Eqs/pair_mdf-6.jpg" />
<p>The following coefficients must be defined for each pair of atoms
types via the pair_coeff command as in the examples above, or in the
data file or restart files read by the read_data or read_restart
commands, or by mixing as described below:</p>
<ul class="simple">
<li>A (energy-distance^12 units)</li>
<li>B (energy-distance^6 units)</li>
<li>r_m (distance units)</li>
<li>r_*cut* (distance units)</li>
</ul>
<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 and sigma coefficients
and cutoff distance for all of the lj/cut pair styles can be mixed.
The default mix value is <em>geometric</em>. See the &#8220;pair_modify&#8221; command
for details.</p>
<p>All of the <em>lj/cut</em> pair styles support the
<a class="reference internal" href="pair_modify.html"><em>pair_modify</em></a> shift option for the energy of the
Lennard-Jones portion of the pair interaction.</p>
<p>The <em>lj/cut/coul/long</em> and <em>lj/cut/tip4p/long</em> pair styles support the
<a class="reference internal" href="pair_modify.html"><em>pair_modify</em></a> table option since they can tabulate
the short-range portion of the long-range Coulombic interaction.</p>
<p>All of the <em>lj/cut</em> pair styles support the
<a class="reference internal" href="pair_modify.html"><em>pair_modify</em></a> tail option for adding a long-range
tail correction to the energy and pressure for the Lennard-Jones
portion of the pair interaction.</p>
<p>All of the <em>lj/cut</em> pair styles write their information to <a class="reference internal" href="restart.html"><em>binary restart files</em></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>The <em>lj/cut</em> and <em>lj/cut/coul/long</em> pair styles support the use of the
<em>inner</em>, <em>middle</em>, and <em>outer</em> keywords of the <a class="reference internal" href="run_style.html"><em>run_style respa</em></a> command, meaning the pairwise forces can be
partitioned by distance at different levels of the rRESPA hierarchy.
The other styles only support the <em>pair</em> keyword of run_style respa.
See the <a class="reference internal" href="run_style.html"><em>run_style</em></a> command for details.</p>
</div>
<hr class="docutils" />
<div class="section" id="restrictions">
<h2>Restrictions<a class="headerlink" href="#restrictions" title="Permalink to this headline">¶</a></h2>
<p>These pair styles can only be used if LAMMPS was built with the
USER-MISC package. See the <a class="reference internal" href="Section_start.html#start-3"><span>Making LAMMPS</span></a>
section for more info on packages.</p>
</div>
<div class="section" id="related-commands">
<h2>Related commands<a class="headerlink" href="#related-commands" title="Permalink to this headline">¶</a></h2>
<p><a class="reference internal" href="pair_coeff.html"><em>pair_coeff</em></a></p>
<p><strong>Default:</strong> none</p>
<hr class="docutils" />
<p id="mei"><strong>(Mei)</strong> Mei, Davenport, Fernando, Phys Rev B, 43 4653 (1991)</p>
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