74 lines
1.7 KiB
ReStructuredText
74 lines
1.7 KiB
ReStructuredText
.. index:: angle_style cosine/periodic
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.. index:: angle_style cosine/periodic/omp
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angle_style cosine/periodic command
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===================================
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Accelerator Variants: *cosine/periodic/omp*
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Syntax
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""""""
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.. code-block:: LAMMPS
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angle_style cosine/periodic
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Examples
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""""""""
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.. code-block:: LAMMPS
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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 may be
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particularly used for organometallic systems where :math:`n` = 4 might be used
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for an octahedral complex and :math:`n` = 3 might be used for a trigonal
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center:
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.. math::
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E = \frac{2.0}{n^2} * C \left[ 1 - B(-1)^n\cos\left( n\theta\right) \right]
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where :math:`C`, :math:`B` and :math:`n` are coefficients defined for each angle type.
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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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* :math:`C` (energy)
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* :math:`B` = 1 or -1
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* :math:`n` = 1, 2, 3, 4, 5 or 6 for periodicity
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Note that the prefactor :math:`C` is specified as coefficient and not the overall force
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constant :math:`K = \frac{2 C}{n^2}`. When :math:`B = 1`, it leads to a minimum for the
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linear geometry. When :math:`B = -1`, it leads to a maximum for the linear geometry.
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----------
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.. include:: accel_styles.rst
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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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EXTRA-MOLECULE package. See the :doc:`Build package <Build_package>` doc page
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for more info.
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Related commands
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""""""""""""""""
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:doc:`angle_coeff <angle_coeff>`
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Default
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"""""""
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none
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