.. 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