73 lines
1.7 KiB
ReStructuredText
73 lines
1.7 KiB
ReStructuredText
.. index:: improper_style inversion/harmonic
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improper_style inversion/harmonic 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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improper_style inversion/harmonic
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Examples
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""""""""
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.. code-block:: LAMMPS
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improper_style inversion/harmonic
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improper_coeff 1 18.776340 0.000000
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Description
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"""""""""""
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The *inversion/harmonic* improper style follows the Wilson-Decius
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out-of-plane angle definition and uses an harmonic potential:
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.. math::
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E = K \left(\omega - \omega_0\right)^2
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where :math:`K` is the force constant and :math:`\omega` is the angle
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evaluated for all three axis-plane combinations centered around the atom I.
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For the IL axis and the IJK plane :math:`\omega` looks as follows:
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.. image:: JPG/umbrella.jpg
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:align: center
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Note that the *inversion/harmonic* angle term evaluation differs to
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the :doc:`improper_umbrella <improper_umbrella>` due to the cyclic
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evaluation of all possible angles :math:`\omega`.
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The following coefficients must be defined for each improper type via
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the :doc:`improper_coeff <improper_coeff>` command as in the example
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above, or in the data file or restart files read by the
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:doc:`read_data <read_data>` or :doc:`read_restart <read_restart>`
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commands:
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* :math:`K` (energy)
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* :math:`\omega_0` (degrees)
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If :math:`\omega_0 = 0` the potential term has a single minimum for
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the planar structure. Otherwise it has two minima at +/- :math:`\omega_0`,
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with a barrier in between.
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----------
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Restrictions
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""""""""""""
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This improper style can only be used if LAMMPS was built with the
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MOFFF 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:`improper_coeff <improper_coeff>`
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Default
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"""""""
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none
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