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<div class="section" id="improper-style-ring-command">
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<span id="index-0"></span><h1>improper_style ring command<a class="headerlink" href="#improper-style-ring-command" title="Permalink to this headline">¶</a></h1>
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<div class="section" id="improper-style-ring-omp-command">
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<h1>improper_style ring/omp command<a class="headerlink" href="#improper-style-ring-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>improper_style ring
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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>improper_style ring
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improper_coeff 1 8000 70.5
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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>ring</em> improper style uses the potential</p>
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<img alt="_images/improper_ring.jpg" class="align-center" src="_images/improper_ring.jpg" />
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<p>where K is a prefactor, theta is the angle formed by the atoms
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specified by (i,j,k,l) indices and theta0 its equilibrium value.</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"><em>read_data</em></a> command) are ordered i,j,k,l then
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theta_*ijl* is the angle between atoms i,j and l, theta_*ijk* is the
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angle between atoms i,j and k, theta_*kjl* is the angle between atoms
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j,k, and l.</p>
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<p>The “ring” improper style implements the improper potential introduced
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by Destree et al., in Equation (9) of <a class="reference internal" href="#destree"><span>(Destree)</span></a>. This
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potential does not affect small amplitude vibrations but is used in an
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ad-hoc way to prevent the onset of accidentially large amplitude
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fluctuations leading to the occurrence of a planar conformation of the
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three bonds i-j, j-k and j-l, an intermediate conformation toward the
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chiral inversion of a methine carbon. In the “Impropers” section of
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data file four atoms: i, j, k and l are specified with i,j and l lying
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on the backbone of the chain and k specifying the chirality of j.</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"><em>improper_coeff</em></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"><em>read_data</em></a> or <a class="reference internal" href="read_restart.html"><em>read_restart</em></a>
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commands:</p>
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<ul class="simple">
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<li>K (energy/radian^2)</li>
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<li>theta0 (degrees)</li>
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</ul>
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<p>theta0 is specified in degrees, but LAMMPS converts it to radians
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internally; hence the units of K are in energy/radian^2.</p>
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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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<hr class="docutils" />
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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 improper 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="improper_coeff.html"><em>improper_coeff</em></a></p>
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<p id="destree"><strong>(Destree)</strong> M. Destree, F. Laupretre, A. Lyulin, and J.-P. Ryckaert,
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J Chem Phys, 112, 9632 (2000).</p>
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