95 lines
2.8 KiB
ReStructuredText
95 lines
2.8 KiB
ReStructuredText
.. index:: improper_style cvff
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improper_style cvff command
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===========================
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improper_style cvff/intel command
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=================================
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improper_style cvff/omp 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 cvff
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Examples
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""""""""
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.. code-block:: LAMMPS
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improper_style cvff
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improper_coeff 1 80.0 -1 4
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Description
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"""""""""""
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The *cvff* improper style uses the potential
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.. math::
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E = K [1 + d \cos (n \phi) ]
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where phi is the improper dihedral angle.
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If the 4 atoms in an improper quadruplet (listed in the data file read
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by the :doc:`read_data <read_data>` command) are ordered I,J,K,L then
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the improper dihedral angle is between the plane of I,J,K and the
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plane of J,K,L. Note that because this is effectively a dihedral
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angle, the formula for this improper style is the same as for
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:doc:`dihedral_style harmonic <dihedral_harmonic>`.
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Note that defining 4 atoms to interact in this way, does not mean that
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bonds necessarily exist between I-J, J-K, or K-L, as they would in a
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linear dihedral. Normally, the bonds I-J, I-K, I-L would exist for an
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improper to be defined between the 4 atoms.
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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:`d` (+1 or -1)
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* :math:`n` (0,1,2,3,4,6)
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----------
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Styles with a *gpu*\ , *intel*\ , *kk*\ , *omp*\ , or *opt* suffix are
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functionally the same as the corresponding style without the suffix.
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They have been optimized to run faster, depending on your available
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hardware, as discussed on the :doc:`Speed packages <Speed_packages>` doc
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page. The accelerated styles take the same arguments and should
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produce the same results, except for round-off and precision issues.
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These accelerated styles are part of the GPU, USER-INTEL, KOKKOS,
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USER-OMP and OPT packages, respectively. They are only enabled if
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LAMMPS was built with those packages. See the :doc:`Build package <Build_package>` doc page for more info.
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You can specify the accelerated styles explicitly in your input script
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by including their suffix, or you can use the :doc:`-suffix command-line switch <Run_options>` when you invoke LAMMPS, or you can use the
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:doc:`suffix <suffix>` command in your input script.
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See the :doc:`Speed packages <Speed_packages>` doc page for more
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instructions on how to use the accelerated styles effectively.
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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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MOLECULE package. See the :doc:`Build package <Build_package>` doc page
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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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