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<li>dihedral_coeff command</li>
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<div class="section" id="dihedral-coeff-command">
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<span id="index-0"></span><h1>dihedral_coeff 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_coeff</span> <span class="n">N</span> <span class="n">args</span>
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</pre></div>
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</div>
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<ul class="simple">
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<li>N = dihedral type (see asterisk form below)</li>
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<li>args = coefficients for one or more dihedral types</li>
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</ul>
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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">dihedral_coeff</span> <span class="mi">1</span> <span class="mf">80.0</span> <span class="mi">1</span> <span class="mi">3</span>
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<span class="n">dihedral_coeff</span> <span class="o">*</span> <span class="mf">80.0</span> <span class="mi">1</span> <span class="mi">3</span> <span class="mf">0.5</span>
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<span class="n">dihedral_coeff</span> <span class="mi">2</span><span class="o">*</span> <span class="mf">80.0</span> <span class="mi">1</span> <span class="mi">3</span> <span class="mf">0.5</span>
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</pre></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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<hr class="docutils" />
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<p>Specify the dihedral force field coefficients for one or more dihedral types.
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The number and meaning of the coefficients depends on the dihedral style.
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Dihedral coefficients can also be set in the data file read by the
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<a class="reference internal" href="read_data.html"><span class="doc">read_data</span></a> command or in a restart file.</p>
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<p>N can be specified in one of two ways. An explicit numeric value can
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be used, as in the 1st example above. Or a wild-card asterisk can be
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used to set the coefficients for multiple dihedral types. This takes the
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form “*” or “<em>n” or “n</em>” or “m*n”. If N = the number of dihedral types,
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then an asterisk with no numeric values means all types from 1 to N. A
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leading asterisk means all types from 1 to n (inclusive). A trailing
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asterisk means all types from n to N (inclusive). A middle asterisk
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means all types from m to n (inclusive).</p>
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<p>Note that using a dihedral_coeff command can override a previous setting
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for the same dihedral type. For example, these commands set the coeffs
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for all dihedral types, then overwrite the coeffs for just dihedral type 2:</p>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">dihedral_coeff</span> <span class="o">*</span> <span class="mf">80.0</span> <span class="mi">1</span> <span class="mi">3</span>
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<span class="n">dihedral_coeff</span> <span class="mi">2</span> <span class="mf">200.0</span> <span class="mi">1</span> <span class="mi">3</span>
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</pre></div>
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</div>
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<p>A line in a data file that specifies dihedral coefficients uses the exact
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same format as the arguments of the dihedral_coeff command in an input
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script, except that wild-card asterisks should not be used since
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coefficients for all N types must be listed in the file. For example,
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under the “Dihedral Coeffs” section of a data file, the line that
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corresponds to the 1st example above would be listed as</p>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="mi">1</span> <span class="mf">80.0</span> <span class="mi">1</span> <span class="mi">3</span>
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</pre></div>
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</div>
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<p>The <a class="reference internal" href="dihedral_class2.html"><span class="doc">dihedral_style class2</span></a> is an exception to
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this rule, in that an additional argument is used in the input script
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to allow specification of the cross-term coefficients. See its doc
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page for details.</p>
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<div class="admonition note">
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<p class="first admonition-title">Note</p>
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<p class="last">When comparing the formulas and coefficients for various LAMMPS
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dihedral styles with dihedral equations defined by other force fields,
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note that some force field implementations divide/multiply the energy
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prefactor <em>K</em> by the multiple number of torsions that contain the J-K
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bond in an I-J-K-L torsion. LAMMPS does not do this, i.e. the listed
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dihedral equation applies to each individual dihedral. Thus you need
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to define <em>K</em> appropriately to account for this difference if
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necessary.</p>
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</div>
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<hr class="docutils" />
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<p>Here is an alphabetic list of dihedral styles defined in LAMMPS. Click on
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the style to display the formula it computes and coefficients
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specified by the associated <a class="reference internal" href="#"><span class="doc">dihedral_coeff</span></a> command.</p>
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<p>Note that there are also additional dihedral styles submitted by users
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which are included in the LAMMPS distribution. The list of these with
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links to the individual styles are given in the dihedral section of
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<a class="reference internal" href="Section_commands.html#cmd-5"><span class="std std-ref">this page</span></a>.</p>
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<ul class="simple">
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<li><a class="reference internal" href="dihedral_none.html"><span class="doc">dihedral_style none</span></a> - turn off dihedral interactions</li>
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<li><a class="reference internal" href="dihedral_hybrid.html"><span class="doc">dihedral_style hybrid</span></a> - define multiple styles of dihedral interactions</li>
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<li><a class="reference internal" href="dihedral_charmm.html"><span class="doc">dihedral_style charmm</span></a> - CHARMM dihedral</li>
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<li><a class="reference internal" href="dihedral_class2.html"><span class="doc">dihedral_style class2</span></a> - COMPASS (class 2) dihedral</li>
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<li><a class="reference internal" href="dihedral_harmonic.html"><span class="doc">dihedral_style harmonic</span></a> - harmonic dihedral</li>
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<li><a class="reference internal" href="dihedral_helix.html"><span class="doc">dihedral_style helix</span></a> - helix dihedral</li>
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<li><a class="reference internal" href="dihedral_multi_harmonic.html"><span class="doc">dihedral_style multi/harmonic</span></a> - multi-harmonic dihedral</li>
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<li><a class="reference internal" href="dihedral_opls.html"><span class="doc">dihedral_style opls</span></a> - OPLS dihedral</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 command must come after the simulation box is defined by a
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<a class="reference internal" href="read_data.html"><span class="doc">read_data</span></a>, <a class="reference internal" href="read_restart.html"><span class="doc">read_restart</span></a>, or
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<a class="reference internal" href="create_box.html"><span class="doc">create_box</span></a> command.</p>
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<p>A dihedral style must be defined before any dihedral coefficients are
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set, either in the input script or in a data file.</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_style.html"><span class="doc">dihedral_style</span></a></p>
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<p><strong>Default:</strong> none</p>
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