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<div class="section" id="improper-style-ring-command">
<span id="index-0"></span><h1>improper_style ring command</h1>
</div>
<div class="section" id="improper-style-ring-omp-command">
<h1>improper_style ring/omp command</h1>
<div class="section" id="syntax">
<h2>Syntax</h2>
<pre class="literal-block">
improper_style ring
</pre>
</div>
<div class="section" id="examples">
<h2>Examples</h2>
<pre class="literal-block">
improper_style ring
improper_coeff 1 8000 70.5
</pre>
</div>
<div class="section" id="description">
<h2>Description</h2>
<p>The <em>ring</em> improper style uses the potential</p>
<img alt="_images/improper_ring.jpg" class="align-center" src="_images/improper_ring.jpg" />
<p>where K is a prefactor, theta is the angle formed by the atoms
specified by (i,j,k,l) indices and theta0 its equilibrium value.</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"><span class="doc">read_data</span></a> command) are ordered i,j,k,l then
theta_<em>ijl</em> is the angle between atoms i,j and l, theta_<em>ijk</em> is the
angle between atoms i,j and k, theta_<em>kjl</em> is the angle between atoms
j,k, and l.</p>
<p>The &#8220;ring&#8221; improper style implements the improper potential introduced
by Destree et al., in Equation (9) of <a class="reference internal" href="#destree"><span class="std std-ref">(Destree)</span></a>. This
potential does not affect small amplitude vibrations but is used in an
ad-hoc way to prevent the onset of accidentially large amplitude
fluctuations leading to the occurrence of a planar conformation of the
three bonds i-j, j-k and j-l, an intermediate conformation toward the
chiral inversion of a methine carbon. In the &#8220;Impropers&#8221; section of
data file four atoms: i, j, k and l are specified with i,j and l lying
on the backbone of the chain and k specifying the chirality of j.</p>
<p>The following coefficients must be defined for each improper type via
the <a class="reference internal" href="improper_coeff.html"><span class="doc">improper_coeff</span></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"><span class="doc">read_data</span></a> or <a class="reference internal" href="read_restart.html"><span class="doc">read_restart</span></a>
commands:</p>
<ul class="simple">
<li>K (energy/radian^2)</li>
<li>theta0 (degrees)</li>
</ul>
<p>theta0 is specified in degrees, but LAMMPS converts it to radians
internally; hence the units of K are in energy/radian^2.</p>
<hr class="docutils" />
<p>Styles with a <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"><span class="doc">Section_accelerate</span></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 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 class="std std-ref">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 class="std std-ref">-suffix command-line switch</span></a> when you invoke LAMMPS, or you can
use the <a class="reference internal" href="suffix.html"><span class="doc">suffix</span></a> command in your input script.</p>
<p>See <a class="reference internal" href="Section_accelerate.html"><span class="doc">Section_accelerate</span></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</h2>
<p>This improper style can only be used if LAMMPS was built with the
USER-MISC package. 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>
</div>
<div class="section" id="related-commands">
<h2>Related commands</h2>
<p><a class="reference internal" href="improper_coeff.html"><span class="doc">improper_coeff</span></a></p>
<p id="destree"><strong>(Destree)</strong> M. Destree, F. Laupretre, A. Lyulin, and J.-P. Ryckaert,
J Chem Phys, 112, 9632 (2000).</p>
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