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<li class="toctree-l1"><a class="reference internal" href="Section_intro.html">1. Introduction</a></li>
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<li>pair_style lj/mdf command</li>
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<div class="section" id="pair-style-lj-mdf-command">
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<span id="index-0"></span><h1>pair_style lj/mdf command</h1>
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</div>
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<div class="section" id="pair-style-buck-mdf-command">
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<h1>pair_style buck/mdf command</h1>
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</div>
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<div class="section" id="pair-style-lennard-mdf-command">
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<h1>pair_style lennard/mdf command</h1>
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<div class="section" id="syntax">
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<h2>Syntax</h2>
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<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>
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</pre></div>
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</div>
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<ul class="simple">
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<li>style = <em>lj/mdf</em> or <em>buck/mdf</em> or <em>lennard/mdf</em></li>
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<li>args = list of arguments for a particular style</li>
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</ul>
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<pre class="literal-block">
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<em>lj/mdf</em> args = cutoff1 cutoff2
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cutoff1 = inner cutoff for the start of the tapering function
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cutoff1 = out cutoff for the end of the tapering function
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<em>buck/mdf</em> args = cutoff1 cutoff2
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cutoff1 = inner cutoff for the start of the tapering function
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cutoff1 = out cutoff for the end of the tapering function
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<em>lennard/mdf</em> args = cutoff1 cutoff2
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cutoff1 = inner cutoff for the start of the tapering function
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cutoff1 = out cutoff for the end of the tapering function
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</pre>
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</div>
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<div class="section" id="examples">
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<h2>Examples</h2>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">pair_style</span> <span class="n">lj</span><span class="o">/</span><span class="n">mdf</span> <span class="mf">2.5</span> <span class="mf">3.0</span>
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<span class="n">pair_coeff</span> <span class="o">*</span> <span class="o">*</span> <span class="mi">1</span> <span class="mi">1</span>
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<span class="n">pair_coeff</span> <span class="mi">1</span> <span class="mi">1</span> <span class="mi">1</span> <span class="mf">1.1</span> <span class="mf">2.8</span> <span class="mf">3.0</span> <span class="mf">3.2</span>
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</pre></div>
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</div>
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<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="mf">3.0</span>
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<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>
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<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> <span class="mf">3.5</span>
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</pre></div>
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</div>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">pair_style</span> <span class="n">lennard</span><span class="o">/</span><span class="n">mdf</span> <span class="mf">2.5</span> <span class="mf">3.0</span>
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<span class="n">pair_coeff</span> <span class="o">*</span> <span class="o">*</span> <span class="mi">1</span> <span class="mi">1</span>
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<span class="n">pair_coeff</span> <span class="mi">1</span> <span class="mi">1</span> <span class="mi">1</span> <span class="mf">1.1</span> <span class="mf">2.8</span> <span class="mf">3.0</span> <span class="mf">3.2</span>
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</pre></div>
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</div>
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</div>
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<div class="section" id="description">
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<h2>Description</h2>
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<p>The <em>lj/mdf</em>, <em>buck/mdf</em> and <em>lennard/mdf</em> compute the standard 12-6
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Lennard-Jones and Buckingham potential with the addition of a taper
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function that ramps the energy and force smoothly to zero between an
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inner and outer cutoff.</p>
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<img alt="_images/pair_mdf-1.jpg" class="align-center" src="_images/pair_mdf-1.jpg" />
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<p>The tapering, <em>f(r)</em>, is done by using the Mei, Davenport, Fernando
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function <a class="reference internal" href="#mei"><span class="std std-ref">(Mei)</span></a>.</p>
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<img alt="_images/pair_mdf-2.jpg" class="align-center" src="_images/pair_mdf-2.jpg" />
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<p>where</p>
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<img alt="_images/pair_mdf-3.jpg" class="align-center" src="_images/pair_mdf-3.jpg" />
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<p>Here <em>r_m</em> is the inner cutoff radius and <em>r_cut</em> is the outer cutoff
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radius.</p>
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<hr class="docutils" />
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<p>For the <em>lj/mdf</em> pair_style, the potential energy, <em>E(r)</em>, is the
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standard 12-6 Lennard-Jones written in the epsilon/sigma form:</p>
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<img alt="_images/pair_mdf-4.jpg" class="align-center" src="_images/pair_mdf-4.jpg" />
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<p>The following coefficients must be defined for each pair of atoms
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types via the pair_coeff command as in the examples above, or in the
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data file or restart files read by the <a class="reference internal" href="read_data.html"><span class="doc">read_data</span></a> or
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<a class="reference internal" href="read_restart.html"><span class="doc">read_restart commands</span></a>, or by mixing as described
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below:</p>
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<ul class="simple">
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<li>epsilon (energy units)</li>
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<li>sigma (distance units)</li>
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<li>r_m (distance units)</li>
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<li><a href="#id1"><span class="problematic" id="id2">r_</span></a><em>cut</em> (distance units)</li>
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</ul>
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<hr class="docutils" />
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<p>For the <em>buck/mdf</em> pair_style, the potential energy, <em>E(r)</em>, is the
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standard Buckingham potential:</p>
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<img alt="_images/pair_mdf-5.jpg" class="align-center" src="_images/pair_mdf-5.jpg" />
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<ul class="simple">
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<li>A (energy units)</li>
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<li>rho (distance units)</li>
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<li>C (energy-distance^6 units)</li>
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<li>r_m (distance units)</li>
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<li><a href="#id3"><span class="problematic" id="id4">r_</span></a><em>cut</em>$ (distance units)</li>
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</ul>
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<hr class="docutils" />
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<p>For the <em>lennard/mdf</em> pair_style, the potential energy, <em>E(r)</em>, is the
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standard 12-6 Lennard-Jones written in the $A/B$ form:</p>
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<img alt="_images/pair_mdf-6.jpg" class="align-center" src="_images/pair_mdf-6.jpg" />
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<p>The following coefficients must be defined for each pair of atoms
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types via the pair_coeff command as in the examples above, or in the
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data file or restart files read by the read_data or read_restart
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commands, or by mixing as described below:</p>
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<ul class="simple">
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<li>A (energy-distance^12 units)</li>
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<li>B (energy-distance^6 units)</li>
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<li>r_m (distance units)</li>
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<li><a href="#id5"><span class="problematic" id="id6">r_</span></a><em>cut</em> (distance units)</li>
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</ul>
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<hr class="docutils" />
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<p><strong>Mixing, shift, table, tail correction, restart, rRESPA info</strong>:</p>
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<p>For atom type pairs I,J and I != J, the epsilon and sigma coefficients
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and cutoff distance for all of the lj/cut pair styles can be mixed.
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The default mix value is <em>geometric</em>. See the “pair_modify” command
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for details.</p>
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<p>All of the <em>lj/cut</em> pair styles support the
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<a class="reference internal" href="pair_modify.html"><span class="doc">pair_modify</span></a> shift option for the energy of the
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Lennard-Jones portion of the pair interaction.</p>
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<p>The <em>lj/cut/coul/long</em> and <em>lj/cut/tip4p/long</em> pair styles support the
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<a class="reference internal" href="pair_modify.html"><span class="doc">pair_modify</span></a> table option since they can tabulate
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the short-range portion of the long-range Coulombic interaction.</p>
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<p>All of the <em>lj/cut</em> pair styles support the
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<a class="reference internal" href="pair_modify.html"><span class="doc">pair_modify</span></a> tail option for adding a long-range
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tail correction to the energy and pressure for the Lennard-Jones
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portion of the pair interaction.</p>
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<p>All of the <em>lj/cut</em> 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
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not need to be specified in an input script that reads a restart file.</p>
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<p>The <em>lj/cut</em> and <em>lj/cut/coul/long</em> pair styles support the use of the
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<em>inner</em>, <em>middle</em>, and <em>outer</em> keywords of the <a class="reference internal" href="run_style.html"><span class="doc">run_style respa</span></a> command, meaning the pairwise forces can be
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partitioned by distance at different levels of the rRESPA hierarchy.
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The other styles only support the <em>pair</em> keyword of run_style respa.
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See the <a class="reference internal" href="run_style.html"><span class="doc">run_style</span></a> command for details.</p>
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</div>
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<hr class="docutils" />
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<div class="section" id="restrictions">
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<h2>Restrictions</h2>
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<p>These pair styles can only be used if LAMMPS was built with the
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USER-MISC package. See the <a class="reference internal" href="Section_start.html#start-3"><span class="std std-ref">Making LAMMPS</span></a>
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section for more info on packages.</p>
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</div>
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<div class="section" id="related-commands">
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<h2>Related commands</h2>
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<p><a class="reference internal" href="pair_coeff.html"><span class="doc">pair_coeff</span></a></p>
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<p><strong>Default:</strong> none</p>
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<hr class="docutils" />
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<p id="mei"><strong>(Mei)</strong> Mei, Davenport, Fernando, Phys Rev B, 43 4653 (1991)</p>
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