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<li class="toctree-l1"><a class="reference internal" href="Section_intro.html">1. Introduction</a></li>
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<li>dihedral_style spherical command</li>
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<div class="section" id="dihedral-style-spherical-command">
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<span id="index-0"></span><h1>dihedral_style spherical 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">dihedral_style</span> <span class="n">spherical</span>
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</pre></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">dihedral_coeff</span> <span class="mi">1</span> <span class="mi">1</span> <span class="mf">286.1</span> <span class="mi">1</span> <span class="mi">124</span> <span class="mi">1</span> <span class="mi">1</span> <span class="mf">90.0</span> <span class="mi">0</span> <span class="mi">1</span> <span class="mf">90.0</span> <span class="mi">0</span>
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<span class="n">dihedral_coeff</span> <span class="mi">1</span> <span class="mi">3</span> <span class="mf">286.1</span> <span class="mi">1</span> <span class="mi">114</span> <span class="mi">1</span> <span class="mi">1</span> <span class="mi">90</span> <span class="mi">0</span> <span class="mi">1</span> <span class="mf">90.0</span> <span class="mi">0</span> <span class="o">&</span>
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<span class="mf">17.3</span> <span class="mi">0</span> <span class="mf">0.0</span> <span class="mi">0</span> <span class="mi">1</span> <span class="mi">158</span> <span class="mi">1</span> <span class="mi">0</span> <span class="mf">0.0</span> <span class="mi">0</span> <span class="o">&</span>
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<span class="mf">15.1</span> <span class="mi">0</span> <span class="mf">0.0</span> <span class="mi">0</span> <span class="mi">0</span> <span class="mf">0.0</span> <span class="mi">0</span> <span class="mi">1</span> <span class="mf">167.3</span> <span class="mi">1</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>spherical</em> dihedral style uses the potential:</p>
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<img alt="_images/dihedral_spherical_angles.jpg" class="align-center" src="_images/dihedral_spherical_angles.jpg" />
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<img alt="_images/dihedral_spherical.jpg" class="align-center" src="_images/dihedral_spherical.jpg" />
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<p>For this dihedral style, the energy can be any function that combines the
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4-body dihedral-angle (phi) and the two 3-body bond-angles (theta1, theta2).
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For this reason, there is usually no need to define 3-body “angle” forces
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separately for the atoms participating in these interactions.
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It is probably more efficient to incorporate 3-body angle forces into
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the dihedral interaction even if it requires adding additional terms to
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the expansion (as was done in the second example). A careful choice of
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parameters can prevent singularities that occur with traditional
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force-fields whenever theta1 or theta2 approach 0 or 180 degrees.
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The last example above corresponds to an interaction with a single energy
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minima located at phi=114, theta1=158, theta2=167.3 degrees, and it remains
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numerically stable at all angles (phi, theta1, theta2). In this example,
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the coefficients 17.3, and 15.1 can be physically interpreted as the
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harmonic spring constants for theta1 and theta2 around their minima.
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The coefficient 286.1 is the harmonic spring constant for phi after
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division by sin(158)*sin(167.3) (the minima positions for theta1 and theta2).</p>
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<p>The following coefficients must be defined for each dihedral type via the
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<a class="reference internal" href="dihedral_coeff.html"><span class="doc">dihedral_coeff</span></a> command as in the example above, or in
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the Dihedral Coeffs section of a data file file read by the
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<a class="reference internal" href="read_data.html"><span class="doc">read_data</span></a> command:</p>
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<ul class="simple">
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<li>n (integer >= 1)</li>
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<li>C1 (energy)</li>
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<li>K1 (typically an integer)</li>
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<li>a1 (degrees)</li>
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<li>u1 (typically 0.0 or 1.0)</li>
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<li>L1 (typically an integer)</li>
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<li>b1 (degrees, typically 0.0 or 90.0)</li>
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<li>v1 (typically 0.0 or 1.0)</li>
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<li>M1 (typically an integer)</li>
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<li>c1 (degrees, typically 0.0 or 90.0)</li>
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<li>w1 (typically 0.0 or 1.0)</li>
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<li></li>
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<li>Cn (energy)</li>
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<li>Kn (typically an integer)</li>
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<li>an (degrees)</li>
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<li>un (typically 0.0 or 1.0)</li>
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<li>Ln (typically an integer)</li>
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<li>bn (degrees, typically 0.0 or 90.0)</li>
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<li>vn (typically 0.0 or 1.0)</li>
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<li>Mn (typically an integer)</li>
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<li>cn (degrees, typically 0.0 or 90.0)</li>
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<li>wn (typically 0.0 or 1.0)</li>
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</ul>
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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 dihedral 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 class="std std-ref">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</h2>
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<p><a class="reference internal" href="dihedral_coeff.html"><span class="doc">dihedral_coeff</span></a></p>
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<p><strong>Default:</strong> none</p>
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