forked from lijiext/lammps
104 lines
2.9 KiB
Plaintext
104 lines
2.9 KiB
Plaintext
.. 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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.. parsed-literal::
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improper_style cvff
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Examples
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""""""""
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.. parsed-literal::
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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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.. image:: Eqs/improper_cvff.jpg
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:align: center
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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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* K (energy)
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* d (+1 or -1)
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* n (0,1,2,3,4,6)
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----------
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Styles with a *cuda*, *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 in :doc:`Section_accelerate <Section_accelerate>`
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of the manual. The accelerated styles take the same arguments and
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should produce the same results, except for round-off and precision
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issues.
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These accelerated styles are part of the USER-CUDA, GPU, USER-INTEL,
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KOKKOS, USER-OMP and OPT packages, respectively. They are only
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enabled if LAMMPS was built with those packages. See the :ref:`Making LAMMPS <start_3>` section 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 :ref:`-suffix command-line switch <start_7>` when you invoke LAMMPS, or you can
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use the :doc:`suffix <suffix>` command in your input script.
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See :doc:`Section_accelerate <Section_accelerate>` of the manual for
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more 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 (which it is by default). See the :ref:`Making LAMMPS <start_3>` section for more info on packages.
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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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.. _lws: http://lammps.sandia.gov
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.. _ld: Manual.html
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.. _lc: Section_commands.html#comm
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