improper_style sqdistharm command — LAMMPS documentation

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# improper_style sqdistharm command

## Syntax

    improper_style sqdistharm

## Examples

    improper_style sqdistharm
    improper_coeff 1 50.0 0.1

## Description

The sqdistharm improper style uses the potential

\[E = K (d^2 - {d_0}^2)^2\]

where \(d\) is the distance between the central atom and the plane formed by the other three atoms. If the 4 atoms in an improper quadruplet (listed in the data file read by the read_data command) are ordered I,J,K,L then the L-atom is assumed to be the central atom. Note that this is different from the convention used in the improper_style distance.

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/distance^4)

- \({d_0}^2\) (distance^2)

Note that \({d_0}^2\) (in units distance^2) has be provided and not \(d_0\).

## Restrictions

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

## Related commands

improper_coeff

## Default

none