72 lines
1.5 KiB
ReStructuredText
72 lines
1.5 KiB
ReStructuredText
.. index:: angle_style quartic
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.. index:: angle_style quartic/omp
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angle_style quartic command
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===========================
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Accelerator Variants: *quartic/omp*
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Syntax
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""""""
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.. code-block:: LAMMPS
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angle_style quartic
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Examples
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""""""""
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.. code-block:: LAMMPS
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angle_style quartic
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angle_coeff 1 129.1948 56.8726 -25.9442 -14.2221
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Description
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"""""""""""
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The *quartic* angle style uses the potential
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.. math::
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E = K_2 (\theta - \theta_0)^2 + K_3 (\theta - \theta_0)^3 + K_4 (\theta - \theta_0)^4
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where :math:`\theta_0` is the equilibrium value of the angle, and :math:`K` is a
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prefactor. Note that the usual 1/2 factor is included in :math:`K`.
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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:`\theta_0` (degrees)
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* :math:`K_2` (energy)
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* :math:`K_3` (energy)
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* :math:`K_4` (energy)
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:math:`\theta_0` is specified in degrees, but LAMMPS converts it to
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radians internally; hence the various :math:`K` are effectively energy
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per radian\^2 or radian\^3 or radian\^4.
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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
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page 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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