lammps/doc/angle_cosine_shift_exp.txt

"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c

:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Section_commands.html#comm)

:line

angle_style cosine/shift/exp command :h3
angle_style cosine/shift/exp/omp command :h3

[Syntax:]

angle_style cosine/shift/exp :pre

[Examples:]

angle_style cosine/shift/exp
angle_coeff * 10.0 45.0 2.0 :pre

[Description:]

The {cosine/shift/exp} angle style uses the potential

:c,image(Eqs/angle_cosine_shift_exp.jpg)

where Umin, theta, and a are defined for each angle type.

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.

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. In this limit the potential reduces to the
cosineshifted potential.

The following coefficients must be defined for each angle type via the
"angle_coeff"_angle_coeff.html command as in the example above, or in
the data file or restart files read by the "read_data"_read_data.html
or "read_restart"_read_restart.html commands:

umin (energy)
theta (angle)
A (real number) :ul

:line

Styles with a {cuda}, {gpu}, {intel}, {kk}, {omp}, or {opt} 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 "Section_accelerate"_Section_accelerate.html
of the manual.  The accelerated styles take the same arguments and
should produce the same results, except for round-off and precision
issues.

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 "Making
LAMMPS"_Section_start.html#start_3 section for more info.

You can specify the accelerated styles explicitly in your input script
by including their suffix, or you can use the "-suffix command-line
switch"_Section_start.html#start_7 when you invoke LAMMPS, or you can
use the "suffix"_suffix.html command in your input script.

See "Section_accelerate"_Section_accelerate.html of the manual for
more instructions on how to use the accelerated styles effectively.

:line

[Restrictions:]

This angle style can only be used if LAMMPS was built with the
USER-MISC package.  See the "Making LAMMPS"_Section_start.html#start_3
section for more info on packages.

[Related commands:]

"angle_coeff"_angle_coeff.html,
"angle_cosineshift"_angle_cosineshift.html,
"dihedral_cosineshift"_dihedral_cosineshift.html

[Default:] none