64 lines
1.4 KiB
ReStructuredText
64 lines
1.4 KiB
ReStructuredText
.. index:: improper_style sqdistharm
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improper_style sqdistharm 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 sqdistharm
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Examples
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""""""""
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.. code-block:: LAMMPS
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improper_style sqdistharm
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improper_coeff 1 50.0 0.1
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Description
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"""""""""""
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The *sqdistharm* improper style uses the potential
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.. math::
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E = K (d^2 - {d_0}^2)^2
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where :math:`d` is the distance between the central atom and the plane formed
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by the other three atoms. If the 4 atoms in an improper quadruplet
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(listed in the data file read by the :doc:`read_data <read_data>`
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command) are ordered I,J,K,L then the L-atom is assumed to be the
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central atom. Note that this is different from the convention used
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in the improper_style distance.
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The following coefficients must be defined for each improper type via
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the improper_coeff command as in the example above, or in the data
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file or restart files read by the read_data or read_restart commands:
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* :math:`K` (energy/distance\^4)
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* :math:`{d_0}^2` (distance\^2)
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Note that :math:`{d_0}^2` (in units distance\^2) has be provided and not :math:`d_0`.
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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-MISC 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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