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lammps/doc/angle_cosine_periodic.txt
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"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/periodic command :h3
angle_style cosine/periodic/omp command :h3
[Syntax:]
angle_style cosine/periodic :pre
[Examples:]
angle_style cosine/periodic
angle_coeff * 75.0 1 6 :pre
[Description:]
The {cosine/periodic} angle style uses the following potential, which
is commonly used in the "DREIDING"_Section_howto.html#howto_4 force
field, particularly for organometallic systems where {n} = 4 might be
used for an octahedral complex and {n} = 3 might be used for a
trigonal center:
:c,image(Eqs/angle_cosine_periodic.jpg)
where C, B and n are coefficients defined for each angle type.
See "(Mayo)"_#Mayo for a description of the DREIDING force field
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:
C (energy)
B = 1 or -1
n = 1, 2, 3, 4, 5 or 6 for periodicity :ul
Note that the prefactor C is specified and not the overall force
constant K = C / n^2. When B = 1, it leads to a minimum for the
linear geometry. When B = -1, it leads to a maximum for the linear
geometry.
:line
Styles with a {cuda}, {gpu}, {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 "this section"_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-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_6 when you invoke LAMMPS, or you can
use the "suffix"_suffix.html command in your input script.
See "this section"_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
MOLECULAR package (which it is by default). See the "Making
LAMMPS"_Section_start.html#start_3 section for more info on packages.
[Related commands:]
"angle_coeff"_angle_coeff.html
[Default:] none
:line
:link(Mayo)
[(Mayo)] Mayo, Olfason, Goddard III, J Phys Chem, 94, 8897-8909
(1990).
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