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<li>improper_coeff command</li>
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<div class="section" id="improper-coeff-command">
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<span id="index-0"></span><h1>improper_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">improper_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 = improper type (see asterisk form below)</li>
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<li>args = coefficients for one or more improper 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">improper_coeff</span> <span class="mi">1</span> <span class="mf">300.0</span> <span class="mf">0.0</span>
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<span class="n">improper_coeff</span> <span class="o">*</span> <span class="mf">80.2</span> <span class="o">-</span><span class="mi">1</span> <span class="mi">2</span>
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<span class="n">improper_coeff</span> <span class="o">*</span><span class="mi">4</span> <span class="mf">80.2</span> <span class="o">-</span><span class="mi">1</span> <span class="mi">2</span>
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</pre></div>
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<div class="section" id="description">
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<h2>Description</h2>
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<p>Specify the improper force field coefficients for one or more improper
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types. The number and meaning of the coefficients depends on the
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improper style. Improper coefficients can also be set in the data
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file read by the <a class="reference internal" href="read_data.html"><span class="doc">read_data</span></a> command or in a restart
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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 improper types. This takes
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the form “*” or “<em>n” or “n</em>” or “m*n”. If N = the number of improper
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types, then an asterisk with no numeric values means all types from 1
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to N. A leading asterisk means all types from 1 to n (inclusive). A
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trailing asterisk means all types from n to N (inclusive). A middle
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asterisk means all types from m to n (inclusive).</p>
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<p>Note that using an improper_coeff command can override a previous
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setting for the same improper type. For example, these commands set
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the coeffs for all improper types, then overwrite the coeffs for just
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improper type 2:</p>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">improper_coeff</span> <span class="o">*</span> <span class="mf">300.0</span> <span class="mf">0.0</span>
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<span class="n">improper_coeff</span> <span class="mi">2</span> <span class="mf">50.0</span> <span class="mf">0.0</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 improper coefficients uses the
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exact same format as the arguments of the improper_coeff command in an
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input 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 “Improper 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">300.0</span> <span class="mf">0.0</span>
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</pre></div>
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</div>
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<p>The <a class="reference internal" href="improper_class2.html"><span class="doc">improper_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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<hr class="docutils" />
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<p>Here is an alphabetic list of improper 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">improper_coeff</span></a> command.</p>
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<p>Note that there are also additional improper 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 improper 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="improper_none.html"><span class="doc">improper_style none</span></a> - turn off improper interactions</li>
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<li><a class="reference internal" href="improper_hybrid.html"><span class="doc">improper_style hybrid</span></a> - define multiple styles of improper interactions</li>
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<li><a class="reference internal" href="improper_class2.html"><span class="doc">improper_style class2</span></a> - COMPASS (class 2) improper</li>
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<li><a class="reference internal" href="improper_cvff.html"><span class="doc">improper_style cvff</span></a> - CVFF improper</li>
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<li><a class="reference internal" href="improper_harmonic.html"><span class="doc">improper_style harmonic</span></a> - harmonic improper</li>
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<li><a class="reference internal" href="improper_umbrella.html"><span class="doc">improper_style umbrella</span></a> - DREIDING improper</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>An improper style must be defined before any improper 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="improper_style.html"><span class="doc">improper_style</span></a></p>
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<p><strong>Default:</strong> none</p>
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