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improper_cvff.txt
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.. index:: improper_style cvff
improper_style cvff command
===========================
improper_style cvff/intel command
=================================
improper_style cvff/omp command
===============================
Syntax
""""""
.. parsed-literal::
improper_style cvff
Examples
""""""""
.. parsed-literal::
improper_style cvff
improper_coeff 1 80.0 -1 4
Description
"""""""""""
The *cvff* improper style uses the potential
.. image:: Eqs/improper_cvff.jpg
:align: center
where phi is the improper dihedral angle.
If the 4 atoms in an improper quadruplet (listed in the data file read
by the :doc:`read_data <read_data>` command) are ordered I,J,K,L then
the improper dihedral angle is between the plane of I,J,K and the
plane of J,K,L. Note that because this is effectively a dihedral
angle, the formula for this improper style is the same as for
:doc:`dihedral_style harmonic <dihedral_harmonic>`.
Note that defining 4 atoms to interact in this way, does not mean that
bonds necessarily exist between I-J, J-K, or K-L, as they would in a
linear dihedral. Normally, the bonds I-J, I-K, I-L would exist for an
improper to be defined between the 4 atoms.
The following coefficients must be defined for each improper type via
the :doc:`improper_coeff <improper_coeff>` command as in the example
above, or in the data file or restart files read by the
:doc:`read_data <read_data>` or :doc:`read_restart <read_restart>`
commands:
* K (energy)
* d (+1 or -1)
* n (0,1,2,3,4,6)
----------
Styles with a *cuda*, *gpu*, *intel*, *kk*, *omp*, or *opt* suffix are
functionally the same as the corresponding style without the suffix.
They have been optimized to run faster, depending on your available
hardware, as discussed in :doc:`Section_accelerate <Section_accelerate>`
of the manual. The accelerated styles take the same arguments and
should produce the same results, except for round-off and precision
issues.
These accelerated styles are part of the USER-CUDA, GPU, USER-INTEL,
KOKKOS, USER-OMP and OPT packages, respectively. They are only
enabled if LAMMPS was built with those packages. See the :ref:`Making LAMMPS <start_3>` section for more info.
You can specify the accelerated styles explicitly in your input script
by including their suffix, or you can use the :ref:`-suffix command-line switch <start_7>` when you invoke LAMMPS, or you can
use the :doc:`suffix <suffix>` command in your input script.
See :doc:`Section_accelerate <Section_accelerate>` of the manual for
more instructions on how to use the accelerated styles effectively.
----------
Restrictions
""""""""""""
This improper style can only be used if LAMMPS was built with the
MOLECULE package (which it is by default). See the :ref:`Making LAMMPS <start_3>` section for more info on packages.
Related commands
""""""""""""""""
:doc:`improper_coeff <improper_coeff>`
**Default:** none
.. _lws: http://lammps.sandia.gov
.. _ld: Manual.html
.. _lc: Section_commands.html#comm
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