"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c

:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Section_commands.html#comm)

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improper_style ring command :h3
improper_style ring/omp command :h3

[Syntax:]

improper_style ring :pre

[Examples:]

improper_style ring
improper_coeff 1 8000 70.5 :pre

[Description:]

The {ring} improper style uses the potential

:c,image(Eqs/improper_ring.jpg)

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 "read_data"_read_data.html 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 "(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 "improper_coeff"_improper_coeff.html command as in the example
above, or in the data file or restart files read by the
"read_data"_read_data.html or "read_restart"_read_restart.html
commands:

K (energy/radian^2)
theta0 (degrees) :ul

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

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Styles with a {cuda}, {gpu}, {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 "Section_accelerate"_Section_accelerate.html 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-OMP and OPT
packages, respectively.  They are only enabled if LAMMPS was built with
those packages.  See the "Making LAMMPS"_Section_start.html#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 "-suffix command-line
switch"_Section_start.html#start_7 when you invoke LAMMPS, or you can
use the "suffix"_suffix.html command in your input script.

See "Section_accelerate"_Section_accelerate.html of the manual for
more instructions on how to use the accelerated styles effectively.

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[Restrictions:]

This improper style can only be used if LAMMPS was built with the
USER-MISC package.  See the "Making LAMMPS"_Section_start.html#start_3
section for more info on packages.

[Related commands:]

"improper_coeff"_improper_coeff.html

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

