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<div class="section" id="dihedral-style-command">
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<span id="index-0"></span><h1>dihedral_style command<a class="headerlink" href="#dihedral-style-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>dihedral_style style
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</pre></div>
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</div>
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<ul class="simple">
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<li>style = <em>none</em> or <em>hybrid</em> or <em>charmm</em> or <em>class2</em> or <em>harmonic</em> or <em>helix</em> or <em>multi/harmonic</em> or <em>opls</em></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<a class="headerlink" href="#examples" title="Permalink to this headline">¶</a></h2>
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<div class="highlight-python"><div class="highlight"><pre>dihedral_style harmonic
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dihedral_style multi/harmonic
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dihedral_style hybrid harmonic charmm
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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>Set the formula(s) LAMMPS uses to compute dihedral interactions
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between quadruplets of atoms, which remain in force for the duration
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of the simulation. The list of dihedral quadruplets is read in by a
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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> command
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from a data or restart file.</p>
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<p>Hybrid models where dihedrals are computed using different dihedral
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potentials can be setup using the <em>hybrid</em> dihedral style.</p>
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<p>The coefficients associated with a dihedral style can be specified in
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a data or restart file or via the <a class="reference internal" href="dihedral_coeff.html"><em>dihedral_coeff</em></a>
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command.</p>
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<p>All dihedral potentials store their coefficient data in binary restart
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files which means dihedral_style and
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<a class="reference internal" href="dihedral_coeff.html"><em>dihedral_coeff</em></a> commands do not need to be
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re-specified in an input script that restarts a simulation. See the
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<a class="reference internal" href="read_restart.html"><em>read_restart</em></a> command for details on how to do
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this. The one exception is that dihedral_style <em>hybrid</em> only stores
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the list of sub-styles in the restart file; dihedral coefficients need
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to be re-specified.</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 both a dihedral and pair style is defined, the
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<a class="reference internal" href="special_bonds.html"><em>special_bonds</em></a> command often needs to be used to
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turn off (or weight) the pairwise interaction that would otherwise
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exist between 4 bonded atoms.</p>
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</div>
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<p>In the formulas listed for each dihedral style, <em>phi</em> is the torsional
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angle defined by the quadruplet of atoms. This angle has a sign
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convention as shown in this diagram:</p>
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<img alt="_images/dihedral_sign.jpg" class="align-center" src="_images/dihedral_sign.jpg" />
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<p>where the I,J,K,L ordering of the 4 atoms that define the dihedral
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is from left to right.</p>
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<p>This sign convention effects several of the dihedral styles listed
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below (e.g. charmm, helix) in the sense that the energy formula
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depends on the sign of phi, which may be reflected in the value of the
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coefficients you specify.</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 via the
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<a class="reference internal" href="dihedral_coeff.html"><em>dihedral_coeff</em></a> command to account for this
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difference if 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="dihedral_coeff.html"><em>dihedral_coeff</em></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>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"><em>dihedral_style none</em></a> - turn off dihedral interactions</li>
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<li><a class="reference internal" href="dihedral_hybrid.html"><em>dihedral_style hybrid</em></a> - define multiple styles of dihedral interactions</li>
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<li><a class="reference internal" href="dihedral_charmm.html"><em>dihedral_style charmm</em></a> - CHARMM dihedral</li>
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<li><a class="reference internal" href="dihedral_class2.html"><em>dihedral_style class2</em></a> - COMPASS (class 2) dihedral</li>
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<li><a class="reference internal" href="dihedral_harmonic.html"><em>dihedral_style harmonic</em></a> - harmonic dihedral</li>
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<li><a class="reference internal" href="dihedral_helix.html"><em>dihedral_style helix</em></a> - helix dihedral</li>
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<li><a class="reference internal" href="dihedral_multi_harmonic.html"><em>dihedral_style multi/harmonic</em></a> - multi-harmonic dihedral</li>
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<li><a class="reference internal" href="dihedral_opls.html"><em>dihedral_style opls</em></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<a class="headerlink" href="#restrictions" title="Permalink to this headline">¶</a></h2>
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<p>Dihedral styles can only be set for atom styles that allow dihedrals
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to be defined.</p>
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<p>Most dihedral styles are part of the MOLECULE package. They are only
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enabled if LAMMPS was built with that package. See the <a class="reference internal" href="Section_start.html#start-3"><span>Making LAMMPS</span></a> section for more info on packages.
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The doc pages for individual dihedral potentials tell if it is part of
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a package.</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="dihedral_coeff.html"><em>dihedral_coeff</em></a></p>
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</div>
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<div class="section" id="default">
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<h2>Default<a class="headerlink" href="#default" title="Permalink to this headline">¶</a></h2>
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<p>dihedral_style none</p>
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