# 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 USER-MISC package. See the Build package doc page for more info.