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improper_ring.txt
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.. 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 *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
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
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