.. index:: improper_style ring

improper_style ring command
===========================

improper_style ring/omp command
===============================

Syntax
""""""

.. parsed-literal::

   improper_style ring

Examples
""""""""

.. parsed-literal::

   improper_style ring
   improper_coeff 1 8000 70.5

Description
"""""""""""

The *ring* improper style uses the potential

.. image:: Eqs/improper_ring.jpg
   :align: center

where K is a prefactor, theta is the angle formed by the atoms
specified by (i,j,k,l) indices and theta0 its equilibrium value.

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
theta_\ *ijl* is the angle between atoms i,j and l, theta_\ *ijk* is the
angle between atoms i,j and k, theta_\ *kjl* is the angle between atoms
j,k, and l.

The "ring" improper style implements the improper potential introduced
by Destree et al., in Equation (9) of :ref:`(Destree) <Destree>`.  This
potential does not affect small amplitude vibrations but is used in an
ad-hoc way to prevent the onset of accidentially large amplitude
fluctuations leading to the occurrence of a planar conformation of the
three bonds i-j, j-k and j-l, an intermediate conformation toward the
chiral inversion of a methine carbon.  In the "Impropers" section of
data file four atoms: i, j, k and l are specified with i,j and l lying
on the backbone of the chain and k specifying the chirality of j.

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/radian^2)
* theta0 (degrees)

theta0 is specified in degrees, but LAMMPS converts it to radians
internally; hence the units of K are in energy/radian^2.


----------


Styles with a *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 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
USER-MISC package.  See the :ref:`Making LAMMPS <start_3>`
section for more info on packages.

Related commands
""""""""""""""""

:doc:`improper_coeff <improper_coeff>`

.. _Destree:



**(Destree)** M. Destree, F. Laupretre, A. Lyulin, and J.-P.  Ryckaert,
J Chem Phys, 112, 9632 (2000).


.. _lws: http://lammps.sandia.gov
.. _ld: Manual.html
.. _lc: Section_commands.html#comm