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<div class="section" id="improper-style-cvff-command">
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<span id="index-0"></span><h1>improper_style cvff command</h1>
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</div>
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<div class="section" id="improper-style-cvff-intel-command">
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<h1>improper_style cvff/intel command</h1>
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</div>
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<div class="section" id="improper-style-cvff-omp-command">
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<h1>improper_style cvff/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">improper_style</span> <span class="n">cvff</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">improper_style</span> <span class="n">cvff</span>
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<span class="n">improper_coeff</span> <span class="mi">1</span> <span class="mf">80.0</span> <span class="o">-</span><span class="mi">1</span> <span class="mi">4</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>cvff</em> improper style uses the potential</p>
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<img alt="_images/improper_cvff.jpg" class="align-center" src="_images/improper_cvff.jpg" />
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<p>where phi is the improper dihedral angle.</p>
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<p>If the 4 atoms in an improper quadruplet (listed in the data file read
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by the <a class="reference internal" href="read_data.html"><span class="doc">read_data</span></a> command) are ordered I,J,K,L then
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the improper dihedral angle is between the plane of I,J,K and the
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plane of J,K,L. Note that because this is effectively a dihedral
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angle, the formula for this improper style is the same as for
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<a class="reference internal" href="dihedral_harmonic.html"><span class="doc">dihedral_style harmonic</span></a>.</p>
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<p>Note that defining 4 atoms to interact in this way, does not mean that
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bonds necessarily exist between I-J, J-K, or K-L, as they would in a
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linear dihedral. Normally, the bonds I-J, I-K, I-L would exist for an
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improper to be defined between the 4 atoms.</p>
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<p>The following coefficients must be defined for each improper type via
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the <a class="reference internal" href="improper_coeff.html"><span class="doc">improper_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>K (energy)</li>
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<li>d (+1 or -1)</li>
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<li>n (0,1,2,3,4,6)</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"><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 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 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 improper style can only be used if LAMMPS was built with the
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MOLECULE package (which it is by default). 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 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="improper_coeff.html"><span class="doc">improper_coeff</span></a></p>
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<p><strong>Default:</strong> none</p>
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