$$

improper_style inversion/harmonic command

Syntax

improper_style inversion/harmonic

Examples

improper_style inversion/harmonic
improper_coeff 1 18.776340 0.000000

Description

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

$$E=K{(\omega -{\omega }_0)}^2$$

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:

Note that the inversion/harmonic angle term evaluation differs to the improper_umbrella due to the cyclic evaluation of all possible angles $\omega$.

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)

• ${\omega }_0$ (degrees)

If ${\omega }_0=0$ the potential term has a single minimum for the planar structure. Otherwise it has two minima at +/- ${\omega }_0$, with a barrier in between.

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Restrictions

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

Related commands

improper_coeff

Default

none