69 lines
1.9 KiB
ReStructuredText
69 lines
1.9 KiB
ReStructuredText
.. index:: angle_style cross
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angle_style cross command
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=========================
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Syntax
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""""""
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.. code-block:: LAMMPS
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angle_style cross
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Examples
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""""""""
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.. code-block:: LAMMPS
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angle_style cross
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angle_coeff 1 200.0 100.0 100.0 1.25 1.25 107.0
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Description
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"""""""""""
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The *cross* angle style uses a potential that couples the bond stretches of
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a bend with the angle stretch of that bend:
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.. math::
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E = K_{SS} \left(r_{12}-r_{12,0}\right)\left(r_{32}-r_{32,0}\right) + K_{BS0}\left(r_{12}-r_{12,0}\right)\left(\theta-\theta_0\right) + K_{BS1}\left(r_{32}-r_{32,0}\right)\left(\theta-\theta_0\right)
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where :math:`r_{12,0}` is the rest value of the bond length between atom 1 and 2,
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:math:`r_{32,0}` is the rest value of the bond length between atom 3 and 2,
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and :math:`\theta_0` is the rest value of the angle. :math:`K_{SS}` is the force constant of
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the bond stretch-bond stretch term and :math:`K_{BS0}` and :math:`K_{BS1}` are the force constants
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of the bond stretch-angle stretch terms.
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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:`K_{SS}` (energy/distance\^2)
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* :math:`K_{BS0}` (energy/distance)
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* :math:`K_{BS1}` (energy/distance)
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* :math:`r_{12,0}` (distance)
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* :math:`r_{32,0}` (distance)
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* :math:`\theta_0` (degrees)
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:math:`\theta_0` is specified in degrees, but LAMMPS converts it to
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radians internally; hence the :math:`K_{BS0}` and :math:`K_{BS1}` are
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effectively energy/distance per radian.
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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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YAFF 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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