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lammps/doc/improper_harmonic.txt
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"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)
:line
improper_style harmonic command :h3
improper_style harmonic/omp command :h3
[Syntax:]
improper_style harmonic :pre
[Examples:]
improper_style harmonic
improper_coeff 1 100.0 0 :pre
[Description:]
The {harmonic} improper style uses the potential
:c,image(Eqs/improper_harmonic.jpg)
where X is the improper angle, X0 is its equilibrium value, and K is a
prefactor. Note that the usual 1/2 factor is included in K.
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 X
is the angle between the plane of I,J,K and the plane of J,K,L.
Alternatively, you can think of atoms J,K,L as being in a plane, and
atom I above the plane, and X as a measure of how far out-of-plane I
is with respect to the other 3 atoms.
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 "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)
X0 (degrees) :ul
X0 is specified in degrees, but LAMMPS converts it to radians
internally; hence the units of K are in energy/radian^2.
:line
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 "this section"_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_6 when you invoke LAMMPS, or you can
use the "suffix"_suffix.html command in your input script.
See "this section"_Section_accelerate.html of the manual for more
instructions on how to use the accelerated styles effectively.
:line
[Restrictions:]
This improper style can only be used if LAMMPS was built with the
MOLECULAR package (which it is by default). See the "Making
LAMMPS"_Section_start.html#start_3 section for more info on packages.
[Related commands:]
"improper_coeff"_improper_coeff.html
[Default:] none
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