forked from lijiext/lammps
110 lines
2.9 KiB
Plaintext
110 lines
2.9 KiB
Plaintext
.. index:: angle_style cosine/periodic
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angle_style cosine/periodic command
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===================================
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angle_style cosine/periodic/omp command
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=======================================
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Syntax
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""""""
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.. parsed-literal::
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angle_style cosine/periodic
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Examples
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""""""""
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.. parsed-literal::
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angle_style cosine/periodic
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angle_coeff * 75.0 1 6
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Description
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"""""""""""
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The *cosine/periodic* angle style uses the following potential, which
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is commonly used in the :ref:`DREIDING <howto_4>` force
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field, particularly for organometallic systems where *n* = 4 might be
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used for an octahedral complex and *n* = 3 might be used for a
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trigonal center:
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.. image:: Eqs/angle_cosine_periodic.jpg
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:align: center
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where C, B and n are coefficients defined for each angle type.
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See :ref:`(Mayo) <cosine-Mayo>` for a description of the DREIDING force field
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The following coefficients must be defined for each angle type via the
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:doc:`angle_coeff <angle_coeff>` command as in the example above, or in
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the data file or restart files read by the :doc:`read_data <read_data>`
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or :doc:`read_restart <read_restart>` commands:
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* C (energy)
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* B = 1 or -1
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* n = 1, 2, 3, 4, 5 or 6 for periodicity
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Note that the prefactor C is specified and not the overall force
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constant K = C / n^2. When B = 1, it leads to a minimum for the
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linear geometry. When B = -1, it leads to a maximum for the linear
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geometry.
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----------
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Styles with a *gpu*\ , *intel*\ , *kk*\ , *omp*\ , or *opt* suffix are
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functionally the same as the corresponding style without the suffix.
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They have been optimized to run faster, depending on your available
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hardware, as discussed in :doc:`Section_accelerate <Section_accelerate>`
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of the manual. The accelerated styles take the same arguments and
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should produce the same results, except for round-off and precision
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issues.
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These accelerated styles are part of the GPU, USER-INTEL, KOKKOS,
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USER-OMP and OPT packages, respectively. They are only enabled if
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LAMMPS was built with those packages. See the :ref:`Making LAMMPS <start_3>` section for more info.
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You can specify the accelerated styles explicitly in your input script
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by including their suffix, or you can use the :ref:`-suffix command-line switch <start_7>` when you invoke LAMMPS, or you can
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use the :doc:`suffix <suffix>` command in your input script.
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See :doc:`Section_accelerate <Section_accelerate>` of the manual for
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more instructions on how to use the accelerated styles effectively.
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----------
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Restrictions
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""""""""""""
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This angle style can only be used if LAMMPS was built with the
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MOLECULE package (which it is by default). See the :ref:`Making LAMMPS <start_3>` section for more info on packages.
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Related commands
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""""""""""""""""
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:doc:`angle_coeff <angle_coeff>`
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**Default:** none
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----------
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.. _cosine-Mayo:
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**(Mayo)** Mayo, Olfason, Goddard III, J Phys Chem, 94, 8897-8909
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(1990).
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.. _lws: http://lammps.sandia.gov
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.. _ld: Manual.html
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.. _lc: Section_commands.html#comm
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