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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_accelerate.html">5. Accelerating LAMMPS performance</a></li>
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<li>dihedral_style cosine/shift/exp command</li>
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<div class="section" id="dihedral-style-cosine-shift-exp-command">
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<span id="index-0"></span><h1>dihedral_style cosine/shift/exp command</h1>
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</div>
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<div class="section" id="dihedral-style-cosine-shift-exp-omp-command">
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<h1>dihedral_style cosine/shift/exp/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">dihedral_style</span> <span class="n">cosine</span><span class="o">/</span><span class="n">shift</span><span class="o">/</span><span class="n">exp</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="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">dihedral_style</span> <span class="n">cosine</span><span class="o">/</span><span class="n">shift</span><span class="o">/</span><span class="n">exp</span>
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<span class="n">dihedral_coeff</span> <span class="mi">1</span> <span class="mf">10.0</span> <span class="mf">45.0</span> <span class="mf">2.0</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>The <em>cosine/shift/exp</em> dihedral style uses the potential</p>
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<img alt="_images/dihedral_cosine_shift_exp.jpg" class="align-center" src="_images/dihedral_cosine_shift_exp.jpg" />
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<p>where Umin, theta, and a are defined for each dihedral type.</p>
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<p>The potential is bounded between [-Umin:0] and the minimum is located
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at the angle theta0. The a parameter can be both positive or negative
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and is used to control the spring constant at the equilibrium.</p>
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<p>The spring constant is given by k=a exp(a) Umin/ [2 (Exp(a)-1)].
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For a>3 k/Umin = a/2 to better than 5% relative error. For negative
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values of the a parameter, the spring constant is essentially zero,
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and anharmonic terms takes over. The potential is furthermore well
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behaved in the limit a->0, where it has been implemented to linear
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order in a for a < 0.001.</p>
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<p>The following coefficients must be defined for each dihedral type via
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the <a class="reference internal" href="dihedral_coeff.html"><span class="doc">dihedral_coeff</span></a> command as in the example
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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:</p>
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<ul class="simple">
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<li>umin (energy)</li>
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<li>theta (angle)</li>
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<li>A (real number)</li>
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</ul>
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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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</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>This dihedral style 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="dihedral_coeff.html"><span class="doc">dihedral_coeff</span></a>,
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<a class="reference internal" href="angle_cosine_shift_exp.html"><span class="doc">angle_cosine_shift_exp</span></a></p>
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<p><strong>Default:</strong> none</p>
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