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### improper_style umbrella command

Syntax:

    improper_style umbrella

Examples:

    improper_style umbrella
    improper_coeff 1 100.0 180.0

Description:

The umbrella improper style uses the following potential, which is commonly referred to as a classic inversion and used in the DREIDING force field:

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

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) for a description of the DREIDING force field.

The following coefficients must be defined for each improper type via the improper_coeff command as in the example above, or in the data file or restart files read by the read_data or read_restart commands:

- K (energy)
- omega0 (degrees)

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 for more info on packages.

Related commands:

improper_coeff

Default: none

(Mayo) Mayo, Olfason, Goddard III, J Phys Chem, 94, 8897-8909 (1990),