# improper_style distance command

## Syntax

``` LAMMPS
improper_style distance
```

## Examples

``` LAMMPS
improper_style distance
improper_coeff 1 80.0 100.0
```

## Description

The *distance* improper style uses the potential

$$E = K_2 d^2 + K_4 d^4$$

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](read_data) command) are
ordered I,J,K,L then the I-atom is assumed to be the central atom.

![image](JPG/improper_distance.jpg){.align-center}

Note that defining 4 atoms to interact in this way, does not mean that
bonds necessarily exist between I-J, J-K, or K-L, as they would in a
linear dihedral. Normally, the bonds I-J, I-K, I-L would exist for an
improper to be defined between the 4 atoms.

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:

-   $K_2$ (energy/distance\^2)
-   $K_4$ (energy/distance\^4)

------------------------------------------------------------------------

## Restrictions

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

## Related commands

[improper_coeff](improper_coeff)

## Default

none