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<title>angle_style cosine/shift/exp command — LAMMPS 15 May 2015 version documentation</title>
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<li>angle_style cosine/shift/exp command</li>
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<div class="section" id="angle-style-cosine-shift-exp-command">
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<span id="index-0"></span><h1>angle_style cosine/shift/exp command<a class="headerlink" href="#angle-style-cosine-shift-exp-command" title="Permalink to this headline">¶</a></h1>
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<div class="section" id="angle-style-cosine-shift-exp-omp-command">
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<h1>angle_style cosine/shift/exp/omp command<a class="headerlink" href="#angle-style-cosine-shift-exp-omp-command" title="Permalink to this headline">¶</a></h1>
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<div class="section" id="syntax">
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<h2>Syntax<a class="headerlink" href="#syntax" title="Permalink to this headline">¶</a></h2>
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<div class="highlight-python"><div class="highlight"><pre>angle_style cosine/shift/exp
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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<a class="headerlink" href="#examples" title="Permalink to this headline">¶</a></h2>
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<div class="highlight-python"><div class="highlight"><pre>angle_style cosine/shift/exp
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angle_coeff * 10.0 45.0 2.0
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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<a class="headerlink" href="#description" title="Permalink to this headline">¶</a></h2>
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<p>The <em>cosine/shift/exp</em> angle style uses the potential</p>
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<img alt="_images/angle_cosine_shift_exp.jpg" class="align-center" src="_images/angle_cosine_shift_exp.jpg" />
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<p>where Umin, theta, and a are defined for each angle type.</p>
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<p>The potential is bounded between [-Umin:0] and the minimum is
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located at the angle theta0. The a parameter can be both positive or
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negative and is used to control the spring constant at the
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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. In this limit the potential reduces to the
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cosineshifted potential.</p>
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<p>The following coefficients must be defined for each angle type via the
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<a class="reference internal" href="angle_coeff.html"><em>angle_coeff</em></a> command as in the example above, or in
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the data file or restart files read by the <a class="reference internal" href="read_data.html"><em>read_data</em></a>
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or <a class="reference internal" href="read_restart.html"><em>read_restart</em></a> 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>cuda</em>, <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"><em>Section_accelerate</em></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 USER-CUDA, GPU, USER-INTEL,
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KOKKOS, USER-OMP and OPT packages, respectively. They are only
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enabled if LAMMPS was built with those packages. See the <a class="reference internal" href="Section_start.html#start-3"><span>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>-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"><em>suffix</em></a> command in your input script.</p>
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<p>See <a class="reference internal" href="Section_accelerate.html"><em>Section_accelerate</em></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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<div class="section" id="restrictions">
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<h2>Restrictions<a class="headerlink" href="#restrictions" title="Permalink to this headline">¶</a></h2>
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<p>This angle 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>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<a class="headerlink" href="#related-commands" title="Permalink to this headline">¶</a></h2>
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<p><a class="reference internal" href="angle_coeff.html"><em>angle_coeff</em></a>,
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<code class="xref doc docutils literal"><span class="pre">angle_cosineshift</span></code>,
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<code class="xref doc docutils literal"><span class="pre">dihedral_cosineshift</span></code></p>
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<p><strong>Default:</strong> none</p>
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