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

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

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improper_style inversion/harmonic command :h3

[Syntax:]

improper_style inversion/harmonic :pre

[Examples:]

improper_style inversion/harmonic
improper_coeff 1 18.776340 0.000000 :pre

[Description:]

The {inversion/harmonic} improper style follows the Wilson-Decius
out-of-plane angle definition and uses an harmonic potential:

:c,image(Eqs/improper_inversion_harmonic.jpg)

where K is the force constant and omega is the angle evaluated for
all three axis-plane combinations centered around the atom I.  For
the IL axis and the IJK plane omega looks as follows:

:c,image(JPG/umbrella.jpg)

Note that the {inversion/harmonic} angle term evaluation differs to
the "improper_umbrella"_improper_umbrella.html due to the cyclic
evaluation of all possible angles omega.

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)
omega0 (degrees) :ul

If omega0 = 0 the potential term has a minimum for the planar
structure.  Otherwise it has two minima at +/- omega0, with a barrier
in between.

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[Restrictions:]

This improper style can only be used if LAMMPS was built with the
USER-MOFFF package.  See the "Build package"_Build_package.html doc
page for more info.

[Related commands:]

"improper_coeff"_improper_coeff.html

[Default:] none

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