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angle_cosine_periodic.txt
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.. index:: angle_style cosine/periodic
angle_style cosine/periodic command
===================================
angle_style cosine/periodic/omp command
=======================================
Syntax
""""""
.. parsed-literal::
angle_style cosine/periodic
Examples
""""""""
.. parsed-literal::
angle_style cosine/periodic
angle_coeff * 75.0 1 6
Description
"""""""""""
The *cosine/periodic* angle style uses the following potential, which
is commonly used in the :ref:`DREIDING <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:
.. image:: Eqs/angle_cosine_periodic.jpg
:align: center
where C, B and n are coefficients defined for each angle type.
See :ref:`(Mayo) <cosine-Mayo>` for a description of the DREIDING force field
The following coefficients must be defined for each angle type via the
:doc:`angle_coeff <angle_coeff>` command as in the example above, or in
the data file or restart files read by the :doc:`read_data <read_data>`
or :doc:`read_restart <read_restart>` commands:
* C (energy)
* B = 1 or -1
* n = 1, 2, 3, 4, 5 or 6 for periodicity
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.
----------
Styles with a *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 :doc:`Section_accelerate <Section_accelerate>`
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 GPU, USER-INTEL, KOKKOS,
USER-OMP and OPT packages, respectively. They are only enabled if
LAMMPS was built with those packages. See the :ref:`Making LAMMPS <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 :ref:`-suffix command-line switch <start_7>` when you invoke LAMMPS, or you can
use the :doc:`suffix <suffix>` command in your input script.
See :doc:`Section_accelerate <Section_accelerate>` of the manual for
more instructions on how to use the accelerated styles effectively.
----------
Restrictions
""""""""""""
This angle style can only be used if LAMMPS was built with the
MOLECULE package (which it is by default). See the :ref:`Making LAMMPS <start_3>` section for more info on packages.
Related commands
""""""""""""""""
:doc:`angle_coeff <angle_coeff>`
**Default:** none
----------
.. _cosine-Mayo:
**(Mayo)** Mayo, Olfason, Goddard III, J Phys Chem, 94, 8897-8909
(1990).
.. _lws: http://lammps.sandia.gov
.. _ld: Manual.html
.. _lc: Section_commands.html#comm
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