<p>where Ed is the dihedral term, Embt is a middle-bond-torsion term,
Eebt is an end-bond-torsion term, Eat is an angle-torsion term, Eaat
is an angle-angle-torsion term, and Ebb13 is a bond-bond-13 term.</p>
<p>Theta1 and theta2 are equilibrium angles and r1 r2 r3 are equilibrium
bond lengths.</p>
<p>See <a class="reference internal" href="pair_modify.html#sun"><span class="std std-ref">(Sun)</span></a> for a description of the COMPASS class2 force field.</p>
<p>Coefficients for the Ed, Embt, Eebt, Eat, Eaat, and Ebb13 formulas
must be defined for each dihedral type via the
<a class="reference internal" href="dihedral_coeff.html"><span class="doc">dihedral_coeff</span></a> command as in the example above,
<p>These are the 6 coefficients for the Ed formula:</p>
<ul class="simple">
<li>K1 (energy)</li>
<li>phi1 (degrees)</li>
<li>K2 (energy)</li>
<li>phi2 (degrees)</li>
<li>K3 (energy)</li>
<li>phi3 (degrees)</li>
</ul>
<p>For the Embt formula, each line in a
<a class="reference internal" href="dihedral_coeff.html"><span class="doc">dihedral_coeff</span></a> command in the input script lists
5 coefficients, the first of which is “mbt” to indicate they are
MiddleBondTorsion coefficients. In a data file, these coefficients
should be listed under a “MiddleBondTorsion Coeffs” heading and you
must leave out the “mbt”, i.e. only list 4 coefficients after the
dihedral type.</p>
<ul class="simple">
<li>mbt</li>
<li>A1 (energy/distance)</li>
<li>A2 (energy/distance)</li>
<li>A3 (energy/distance)</li>
<li>r2 (distance)</li>
</ul>
<p>For the Eebt formula, each line in a
<a class="reference internal" href="dihedral_coeff.html"><span class="doc">dihedral_coeff</span></a> command in the input script lists
9 coefficients, the first of which is “ebt” to indicate they are
EndBondTorsion coefficients. In a data file, these coefficients
should be listed under a “EndBondTorsion Coeffs” heading and you must
leave out the “ebt”, i.e. only list 8 coefficients after the dihedral
type.</p>
<ul class="simple">
<li>ebt</li>
<li>B1 (energy/distance)</li>
<li>B2 (energy/distance)</li>
<li>B3 (energy/distance)</li>
<li>C1 (energy/distance)</li>
<li>C2 (energy/distance)</li>
<li>C3 (energy/distance)</li>
<li>r1 (distance)</li>
<li>r3 (distance)</li>
</ul>
<p>For the Eat formula, each line in a
<a class="reference internal" href="dihedral_coeff.html"><span class="doc">dihedral_coeff</span></a> command in the input script lists
9 coefficients, the first of which is “at” to indicate they are
AngleTorsion coefficients. In a data file, these coefficients should
be listed under a “AngleTorsion Coeffs” heading and you must leave out
the “at”, i.e. only list 8 coefficients after the dihedral type.</p>
<ul class="simple">
<li>at</li>
<li>D1 (energy/radian)</li>
<li>D2 (energy/radian)</li>
<li>D3 (energy/radian)</li>
<li>E1 (energy/radian)</li>
<li>E2 (energy/radian)</li>
<li>E3 (energy/radian)</li>
<li>theta1 (degrees)</li>
<li>theta2 (degrees)</li>
</ul>
<p>Theta1 and theta2 are specified in degrees, but LAMMPS converts them
to radians internally; hence the units of D and E are in
energy/radian.</p>
<p>For the Eaat formula, each line in a
<a class="reference internal" href="dihedral_coeff.html"><span class="doc">dihedral_coeff</span></a> command in the input script lists
4 coefficients, the first of which is “aat” to indicate they are
AngleAngleTorsion coefficients. In a data file, these coefficients
should be listed under a “AngleAngleTorsion Coeffs” heading and you
must leave out the “aat”, i.e. only list 3 coefficients after the
dihedral type.</p>
<ul class="simple">
<li>aat</li>
<li>M (energy/radian^2)</li>
<li>theta1 (degrees)</li>
<li>theta2 (degrees)</li>
</ul>
<p>Theta1 and theta2 are specified in degrees, but LAMMPS converts them
to radians internally; hence the units of M are in energy/radian^2.</p>
<p>For the Ebb13 formula, each line in a
<a class="reference internal" href="dihedral_coeff.html"><span class="doc">dihedral_coeff</span></a> command in the input script lists
4 coefficients, the first of which is “bb13” to indicate they are
BondBond13 coefficients. In a data file, these coefficients should be
listed under a “BondBond13 Coeffs” heading and you must leave out the
“bb13”, i.e. only list 3 coefficients after the dihedral type.</p>
<ul class="simple">
<li>bb13</li>
<li>N (energy/distance^2)</li>
<li>r1 (distance)</li>
<li>r3 (distance)</li>
</ul>
<hr class="docutils" />
<p>Styles with a <em>cuda</em>, <em>gpu</em>, <em>intel</em>, <em>kk</em>, <em>omp</em>, or <em>opt</em> suffix are
functionally the same as the corresponding style without the suffix.
They have been optimized to run faster, depending on your available
hardware, as discussed in <a class="reference internal" href="Section_accelerate.html"><span class="doc">Section_accelerate</span></a>
of the manual. The accelerated styles take the same arguments and
should produce the same results, except for round-off and precision
issues.</p>
<p>These accelerated styles are part of the USER-CUDA, GPU, USER-INTEL,
KOKKOS, USER-OMP and OPT packages, respectively. They are only
enabled if LAMMPS was built with those packages. See the <a class="reference internal" href="Section_start.html#start-3"><span class="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 <a class="reference internal" href="Section_start.html#start-7"><span class="std std-ref">-suffix command-line switch</span></a> when you invoke LAMMPS, or you can
use the <a class="reference internal" href="suffix.html"><span class="doc">suffix</span></a> command in your input script.</p>
<p>See <a class="reference internal" href="Section_accelerate.html"><span class="doc">Section_accelerate</span></a> of the manual for
more instructions on how to use the accelerated styles effectively.</p>
</div>
<hr class="docutils" />
<div class="section" id="restrictions">
<h2>Restrictions</h2>
<p>This dihedral style can only be used if LAMMPS was built with the
CLASS2 package. See the <a class="reference internal" href="Section_start.html#start-3"><span class="std std-ref">Making LAMMPS</span></a>
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