<p>See <aclass="reference internal"href="#improper-sun"><spanclass="std std-ref">(Sun)</span></a> for a description of the COMPASS class2 force field.</p>
<p>Coefficients for the Ei and Eaa formulas must be defined for each
improper type via the <aclass="reference internal"href="improper_coeff.html"><spanclass="doc">improper_coeff</span></a> command as
in the example above, or in the data file or restart files read by the
<aclass="reference internal"href="read_data.html"><spanclass="doc">read_data</span></a> or <aclass="reference internal"href="read_restart.html"><spanclass="doc">read_restart</span></a>
commands.</p>
<p>These are the 2 coefficients for the Ei formula:</p>
<ulclass="simple">
<li>K (energy/radian^2)</li>
<li>X0 (degrees)</li>
</ul>
<p>X0 is specified in degrees, but LAMMPS converts it to radians
internally; hence the units of K are in energy/radian^2.</p>
<p>For the Eaa formula, each line in a
<aclass="reference internal"href="improper_coeff.html"><spanclass="doc">improper_coeff</span></a> command in the input script lists
7 coefficients, the first of which is “aa” to indicate they are
AngleAngle coefficients. In a data file, these coefficients should be
listed under a “AngleAngle Coeffs” heading and you must leave out the
“aa”, i.e. only list 6 coefficients after the improper type.</p>
<ulclass="simple">
<li>aa</li>
<li>M1 (energy/distance)</li>
<li>M2 (energy/distance)</li>
<li>M3 (energy/distance)</li>
<li>theta1 (degrees)</li>
<li>theta2 (degrees)</li>
<li>theta3 (degrees)</li>
</ul>
<p>The theta values are specified in degrees, but LAMMPS converts them to
radians internally; hence the units of M are in energy/radian^2.</p>
<p>These accelerated styles are part of the GPU, USER-INTEL, KOKKOS,
USER-OMP and OPT packages, respectively. They are only enabled if
LAMMPS was built with those packages. See the <aclass="reference internal"href="Section_start.html#start-3"><spanclass="std std-ref">Making LAMMPS</span></a> section for more info.</p>
<p>You can specify the accelerated styles explicitly in your input script
by including their suffix, or you can use the <aclass="reference internal"href="Section_start.html#start-7"><spanclass="std std-ref">-suffix command-line switch</span></a> when you invoke LAMMPS, or you can
use the <aclass="reference internal"href="suffix.html"><spanclass="doc">suffix</span></a> command in your input script.</p>
<p>See <aclass="reference internal"href="Section_accelerate.html"><spanclass="doc">Section_accelerate</span></a> of the manual for
more instructions on how to use the accelerated styles effectively.</p>
</div>
<hrclass="docutils"/>
<divclass="section"id="restrictions">
<h2>Restrictions</h2>
<p>This improper style can only be used if LAMMPS was built with the
CLASS2 package. See the <aclass="reference internal"href="Section_start.html#start-3"><spanclass="std std-ref">Making LAMMPS</span></a>
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