# IMPROPER

Section can be repeated.

Specifies the improper torsion potential of the MM system. [Edit on GitHub]

## Keywords

- ATOMS

- K

- KIND

- PHI0

## Keyword descriptions

ATOMS: string[4]

  Usage: ATOMS {KIND1} {KIND2} {KIND3} {KIND4}

  Defines the atomic kinds involved in the improper tors. [Edit on GitHub]

K: real = [rad^-2*hartree]

  Usage: K {real}

  Defines the force constant of the potential [Edit on GitHub]

KIND: enum = CHARMM

  Usage: KIND CHARMM

  Valid values:

  - `CHARMM` Functional Form (CHARMM): K * [ PHI - PHI0 ]**2

  - `G87` Functional Form (G87|G96|HARMONIC): 0.5 * K * [ PHI - PHI0 ]**2

  - `G96` Functional Form (G87|G96|HARMONIC): 0.5 * K * [ PHI - PHI0 ]**2

  - `HARMONIC` Functional Form (G87|G96|HARMONIC): 0.5 * K * [ PHI - PHI0 ]**2

  Define the kind of improper torsion potential [Edit on GitHub]

PHI0: real = [rad]

  Usage: PHI0 {real}

  Defines the phase of the potential. [Edit on GitHub]