# OPBEND

Section can be repeated.

Specifies the out of plane bend potential of the MM system. (Only defined for atom quadruples which are also defined as an improper pattern in the topology.) [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 opbend. [Edit on GitHub]

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

  Usage: K {real}

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

KIND: enum = HARMONIC

  Usage: KIND HARMONIC

  Valid values:

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

  - `MM2` Functional Form (MM2|MM3|MM4): K * [ PHI - PHI0 ]**2

  - `MM3` Functional Form (MM2|MM3|MM4): K * [ PHI - PHI0 ]**2

  - `MM4` Functional Form (MM2|MM3|MM4): K * [ PHI - PHI0 ]**2

  Define the kind of out of plane bend potential [Edit on GitHub]

PHI0: real = [rad]

  Usage: PHI0 {real}

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