<p>where Umin, theta, and a are defined for each dihedral type.</p>
<p>The potential is bounded between [-Umin:0] and the minimum is located
at the angle theta0. The a parameter can be both positive or negative
and is used to control the spring constant at the equilibrium.</p>
<p>The spring constant is given by k=a exp(a) Umin/ [2 (Exp(a)-1)].
For a>3 k/Umin = a/2 to better than 5% relative error. For negative
values of the a parameter, the spring constant is essentially zero,
and anharmonic terms takes over. The potential is furthermore well
behaved in the limit a->0, where it has been implemented to linear
order in a for a < 0.001.</p>
<p>The following coefficients must be defined for each dihedral type via
the <aclass="reference internal"href="dihedral_coeff.html"><spanclass="doc">dihedral_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>
<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 dihedral style can only be used if LAMMPS was built with the
USER-MISC package. See the <aclass="reference internal"href="Section_start.html#start-3"><spanclass="std std-ref">Making LAMMPS</span></a>
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