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<div class="section" id="improper-coeff-command">
<span id="index-0"></span><h1>improper_coeff command</h1>
<div class="section" id="syntax">
<h2>Syntax</h2>
<pre class="literal-block">
improper_coeff N args
</pre>
<ul class="simple">
<li>N = improper type (see asterisk form below)</li>
<li>args = coefficients for one or more improper types</li>
</ul>
</div>
<div class="section" id="examples">
<h2>Examples</h2>
<pre class="literal-block">
improper_coeff 1 300.0 0.0
improper_coeff * 80.2 -1 2
improper_coeff *4 80.2 -1 2
</pre>
</div>
<div class="section" id="description">
<h2>Description</h2>
<p>Specify the improper force field coefficients for one or more improper
types. The number and meaning of the coefficients depends on the
improper style. Improper coefficients can also be set in the data
file read by the <a class="reference internal" href="read_data.html"><span class="doc">read_data</span></a> command or in a restart
file.</p>
<p>N can be specified in one of two ways. An explicit numeric value can
be used, as in the 1st example above. Or a wild-card asterisk can be
used to set the coefficients for multiple improper types. This takes
the form &#8220;*&#8221; or &#8220;*n&#8221; or &#8220;n*&#8221; or &#8220;m*n&#8221;. If N = the number of improper
types, then an asterisk with no numeric values means all types from 1
to N. A leading asterisk means all types from 1 to n (inclusive). A
trailing asterisk means all types from n to N (inclusive). A middle
asterisk means all types from m to n (inclusive).</p>
<p>Note that using an improper_coeff command can override a previous
setting for the same improper type. For example, these commands set
the coeffs for all improper types, then overwrite the coeffs for just
improper type 2:</p>
<pre class="literal-block">
improper_coeff * 300.0 0.0
improper_coeff 2 50.0 0.0
</pre>
<p>A line in a data file that specifies improper coefficients uses the
exact same format as the arguments of the improper_coeff command in an
input script, except that wild-card asterisks should not be used since
coefficients for all N types must be listed in the file. For example,
under the &#8220;Improper Coeffs&#8221; section of a data file, the line that
corresponds to the 1st example above would be listed as</p>
<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>
</pre></div>
</div>
<p>The <a class="reference internal" href="improper_class2.html"><span class="doc">improper_style class2</span></a> is an exception to
this rule, in that an additional argument is used in the input script
to allow specification of the cross-term coefficients. See its doc
page for details.</p>
<hr class="docutils" />
<p>Here is an alphabetic list of improper styles defined in LAMMPS. Click on
the style to display the formula it computes and coefficients
specified by the associated <a class="reference internal" href="#"><span class="doc">improper_coeff</span></a> command.</p>
<p>Note that there are also additional improper styles submitted by users
which are included in the LAMMPS distribution. The list of these with
links to the individual styles are given in the improper section of
<a class="reference internal" href="Section_commands.html#cmd-5"><span class="std std-ref">this page</span></a>.</p>
<ul class="simple">
<li><a class="reference internal" href="improper_none.html"><span class="doc">improper_style none</span></a> - turn off improper interactions</li>
<li><a class="reference internal" href="improper_hybrid.html"><span class="doc">improper_style hybrid</span></a> - define multiple styles of improper interactions</li>
<li><a class="reference internal" href="improper_class2.html"><span class="doc">improper_style class2</span></a> - COMPASS (class 2) improper</li>
<li><a class="reference internal" href="improper_cvff.html"><span class="doc">improper_style cvff</span></a> - CVFF improper</li>
<li><a class="reference internal" href="improper_harmonic.html"><span class="doc">improper_style harmonic</span></a> - harmonic improper</li>
<li><a class="reference internal" href="improper_umbrella.html"><span class="doc">improper_style umbrella</span></a> - DREIDING improper</li>
</ul>
</div>
<hr class="docutils" />
<div class="section" id="restrictions">
<h2>Restrictions</h2>
<p>This command must come after the simulation box is defined by a
<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
<a class="reference internal" href="create_box.html"><span class="doc">create_box</span></a> command.</p>
<p>An improper style must be defined before any improper coefficients are
set, either in the input script or in a data file.</p>
</div>
<div class="section" id="related-commands">
<h2>Related commands</h2>
<p><a class="reference internal" href="improper_style.html"><span class="doc">improper_style</span></a></p>
<p><strong>Default:</strong> none</p>
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