"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 umbrella command :h3

[Syntax:]

improper_style umbrella :pre

[Examples:]

improper_style umbrella
improper_coeff 1 100.0 180.0 :pre

[Description:]

The {umbrella} improper style uses the following potential, which is
commonly referred to as a classic inversion and used in the
"DREIDING"_Section_howto.html#4_4 force field:

:c,image(Eqs/improper_umbrella.jpg)

where K is the force constant and omega is the angle between the IL
axis and the IJK plane:

:c,image(Eqs/umbrella.jpg)

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.

See "(Mayo)"_#Mayo for a description of the DREIDING force field.

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

[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#2_3 section for more info on packages.

[Related commands:]

"improper_coeff"_improper_coeff.html

[Default:] none

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:link(Mayo)
[(Mayo)] Mayo, Olfason, Goddard III, J Phys Chem, 94, 8897-8909
(1990),
