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<title>pair_style lj/smooth command — LAMMPS documentation</title>
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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 class="toctree-l1"><a class="reference internal" href="Section_start.html">2. Getting Started</a></li>
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<li class="toctree-l1"><a class="reference internal" href="Section_accelerate.html">5. Accelerating LAMMPS performance</a></li>
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<li>pair_style lj/smooth command</li>
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<div class="section" id="pair-style-lj-smooth-command">
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<span id="index-0"></span><h1>pair_style lj/smooth command</h1>
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</div>
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<div class="section" id="pair-style-lj-smooth-omp-command">
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<h1>pair_style lj/smooth/omp 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">lj</span><span class="o">/</span><span class="n">smooth</span> <span class="n">Rin</span> <span class="n">Rc</span>
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</pre></div>
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</div>
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<ul class="simple">
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<li>Rin = inner cutoff beyond which force smoothing will be applied (distance units)</li>
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<li>Rc = outer cutoff for lj/smooth interactions (distance units)</li>
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</ul>
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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">smooth</span> <span class="mf">8.0</span> <span class="mf">10.0</span>
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<span class="n">pair_coeff</span> <span class="o">*</span> <span class="o">*</span> <span class="mf">10.0</span> <span class="mf">1.5</span>
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<span class="n">pair_coeff</span> <span class="mi">1</span> <span class="mi">1</span> <span class="mf">20.0</span> <span class="mf">1.3</span> <span class="mf">7.0</span> <span class="mf">9.0</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>Style <em>lj/smooth</em> computes a LJ interaction with a force smoothing
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applied between the inner and outer cutoff.</p>
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<img alt="_images/pair_lj_smooth.jpg" class="align-center" src="_images/pair_lj_smooth.jpg" />
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<p>The polynomial coefficients C1, C2, C3, C4 are computed by LAMMPS to
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cause the force to vary smoothly from the inner cutoff Rin to the
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outer cutoff Rc.</p>
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<p>At the inner cutoff the force and its 1st derivative
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will match the unsmoothed LJ formula. At the outer cutoff the force
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and its 1st derivative will be 0.0. The inner cutoff cannot be 0.0.</p>
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<div class="admonition note">
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<p class="first admonition-title">Note</p>
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<p class="last">this force smoothing causes the energy to be discontinuous both
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in its values and 1st derivative. This can lead to poor energy
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conservation and may require the use of a thermostat. Plot the energy
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and force resulting from this formula via the
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<a class="reference internal" href="pair_write.html"><span class="doc">pair_write</span></a> command to see the effect.</p>
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</div>
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<p>The following coefficients must be defined for each pair of atoms
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types via the <a class="reference internal" href="pair_coeff.html"><span class="doc">pair_coeff</span></a> command as in the examples
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above, or in the data file or restart files read by the
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<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>
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commands, or by mixing as described 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>innner (distance units)</li>
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<li>outer (distance units)</li>
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</ul>
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<p>The last 2 coefficients are optional inner and outer cutoffs. If not
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specified, the global values for Rin and Rc are used.</p>
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<hr class="docutils" />
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<p>Styles with a <em>gpu</em>, <em>intel</em>, <em>kk</em>, <em>omp</em>, or <em>opt</em> suffix are
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functionally the same as the corresponding style without the suffix.
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They have been optimized to run faster, depending on your available
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hardware, as discussed in <a class="reference internal" href="Section_accelerate.html"><span class="doc">Section_accelerate</span></a>
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of the manual. The accelerated styles take the same arguments and
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should produce the same results, except for round-off and precision
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issues.</p>
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<p>These accelerated styles are part of the GPU, USER-INTEL, KOKKOS,
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USER-OMP and OPT packages, respectively. They are only enabled if
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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>
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<p>You can specify the accelerated styles explicitly in your input script
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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
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use the <a class="reference internal" href="suffix.html"><span class="doc">suffix</span></a> command in your input script.</p>
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<p>See <a class="reference internal" href="Section_accelerate.html"><span class="doc">Section_accelerate</span></a> of the manual for
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more instructions on how to use the accelerated styles effectively.</p>
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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, sigma, Rin
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coefficients and the cutoff distance for this pair style can be mixed.
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Rin is a cutoff value and is mixed like the cutoff. The other
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coefficients are mixed according to the pair_modify mix option. The
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default mix value is <em>geometric</em>. See the “pair_modify” command for
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details.</p>
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<p>This pair style supports the <a class="reference internal" href="pair_modify.html"><span class="doc">pair_modify</span></a> shift
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option for the energy of the pair interaction.</p>
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<p>The <a class="reference internal" href="pair_modify.html"><span class="doc">pair_modify</span></a> table option is not relevant
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for this pair style.</p>
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<p>This pair style does not support the <a class="reference internal" href="pair_modify.html"><span class="doc">pair_modify</span></a>
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tail option for adding long-range tail corrections to energy and
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pressure, since the energy of the pair interaction is smoothed to 0.0
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at the cutoff.</p>
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<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
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to be specified in an input script that reads a restart file.</p>
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<p>This pair style can only be used via the <em>pair</em> keyword of the
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<a class="reference internal" href="run_style.html"><span class="doc">run_style respa</span></a> command. It does not support the
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<em>inner</em>, <em>middle</em>, <em>outer</em> keywords.</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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<blockquote>
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<div>none</div></blockquote>
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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>, <a class="reference internal" href="pair_lj_smooth_linear.html"><span class="doc">pair lj/smooth/linear</span></a></p>
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<p><strong>Default:</strong> none</p>
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