83 lines
1.8 KiB
ReStructuredText
83 lines
1.8 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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.. parsed-literal::
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improper_style inversion/harmonic
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Examples
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""""""""
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.. parsed-literal::
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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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.. image:: Eqs/improper_inversion_harmonic.jpg
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:align: center
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where K is the force constant and omega is the angle evaluated for
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all three axis-plane combinations centered around the atom I. For
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the IL axis and the IJK plane 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 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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* K (energy)
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* omega0 (degrees)
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If omega0 = 0 the potential term has a minimum for the planar
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structure. Otherwise it has two minima at +/- omega0, with a barrier
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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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USER-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:** none
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----------
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.. _lws: http://lammps.sandia.gov
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.. _ld: Manual.html
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.. _lc: Commands_all.html
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