63 lines
1.5 KiB
ReStructuredText
63 lines
1.5 KiB
ReStructuredText
.. index:: angle_style mm3
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angle_style mm3 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 mm3
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Examples
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""""""""
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.. code-block:: LAMMPS
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angle_style mm3
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angle_coeff 1 100.0 107.0
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Description
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"""""""""""
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The *mm3* angle style uses the potential that is anharmonic in the angle
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as defined in :ref:`(Allinger) <mm3-allinger1989>`
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.. math::
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E = K (\theta - \theta_0)^2 \left[ 1 - 0.014(\theta - \theta_0) + 5.6(10)^{-5} (\theta - \theta_0)^2 - 7.0(10)^{-7} (\theta - \theta_0)^3 + 9(10)^{-10} (\theta - \theta_0)^4 \right]
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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. The anharmonic prefactors have units :math:`\deg^{-n}`, for example
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:math:`-0.014 \deg^{-1}`, :math:`5.6 \cdot 10^{-5} \deg^{-2}`, ...
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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` (energy/radian\^2)
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* :math:`\theta_0` (degrees)
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:math:`\theta_0` is specified in degrees, but LAMMPS converts it to radians
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internally; hence the units of :math:`K` are in energy/radian\^2.
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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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USER\_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:** none
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