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<div class="section" id="improper-style-cvff-command">
<span id="index-0"></span><h1>improper_style cvff command<a class="headerlink" href="#improper-style-cvff-command" title="Permalink to this headline">¶</a></h1>
</div>
<div class="section" id="improper-style-cvff-omp-command">
<h1>improper_style cvff/omp command<a class="headerlink" href="#improper-style-cvff-omp-command" title="Permalink to this headline">¶</a></h1>
<div class="section" id="syntax">
<h2>Syntax<a class="headerlink" href="#syntax" title="Permalink to this headline">¶</a></h2>
<div class="highlight-python"><div class="highlight"><pre>improper_style cvff
</pre></div>
</div>
</div>
<div class="section" id="examples">
<h2>Examples<a class="headerlink" href="#examples" title="Permalink to this headline">¶</a></h2>
<div class="highlight-python"><div class="highlight"><pre>improper_style cvff
improper_coeff 1 80.0 -1 4
</pre></div>
</div>
</div>
<div class="section" id="description">
<h2>Description<a class="headerlink" href="#description" title="Permalink to this headline">¶</a></h2>
<p>The <em>cvff</em> improper style uses the potential</p>
<img alt="_images/improper_cvff.jpg" class="align-center" src="_images/improper_cvff.jpg" />
<p>where phi is the improper dihedral angle.</p>
<p>If the 4 atoms in an improper quadruplet (listed in the data file read
by the <a class="reference internal" href="read_data.html"><em>read_data</em></a> command) are ordered I,J,K,L then
the improper dihedral angle is between the plane of I,J,K and the
plane of J,K,L. Note that because this is effectively a dihedral
angle, the formula for this improper style is the same as for
<a class="reference internal" href="dihedral_harmonic.html"><em>dihedral_style harmonic</em></a>.</p>
<p>Note that defining 4 atoms to interact in this way, does not mean that
bonds necessarily exist between I-J, J-K, or K-L, as they would in a
linear dihedral. Normally, the bonds I-J, I-K, I-L would exist for an
improper to be defined between the 4 atoms.</p>
<p>The following coefficients must be defined for each improper type via
the <a class="reference internal" href="improper_coeff.html"><em>improper_coeff</em></a> command as in the example
above, or in the data file or restart files read by the
<a class="reference internal" href="read_data.html"><em>read_data</em></a> or <a class="reference internal" href="read_restart.html"><em>read_restart</em></a>
commands:</p>
<ul class="simple">
<li>K (energy)</li>
<li>d (+1 or -1)</li>
<li>n (0,1,2,3,4,6)</li>
</ul>
<hr class="docutils" />
<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
functionally the same as the corresponding style without the suffix.
They have been optimized to run faster, depending on your available
hardware, as discussed in <a class="reference internal" href="Section_accelerate.html"><em>Section_accelerate</em></a>
of the manual. The accelerated styles take the same arguments and
should produce the same results, except for round-off and precision
issues.</p>
<p>These accelerated styles are part of the USER-CUDA, GPU, USER-INTEL,
KOKKOS, USER-OMP and OPT packages, respectively. They are only
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>
<p>You can specify the accelerated styles explicitly in your input script
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
use the <a class="reference internal" href="suffix.html"><em>suffix</em></a> command in your input script.</p>
<p>See <a class="reference internal" href="Section_accelerate.html"><em>Section_accelerate</em></a> of the manual for
more instructions on how to use the accelerated styles effectively.</p>
</div>
<hr class="docutils" />
<div class="section" id="restrictions">
<h2>Restrictions<a class="headerlink" href="#restrictions" title="Permalink to this headline">¶</a></h2>
<p>This improper style can only be used if LAMMPS was built with the
MOLECULE package (which it is by default). See the <a class="reference internal" href="Section_start.html#start-3"><span>Making LAMMPS</span></a> section for more info on packages.</p>
</div>
<div class="section" id="related-commands">
<h2>Related commands<a class="headerlink" href="#related-commands" title="Permalink to this headline">¶</a></h2>
<p><a class="reference internal" href="improper_coeff.html"><em>improper_coeff</em></a></p>
<p><strong>Default:</strong> none</p>
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