angle_style mm3 command — LAMMPS documentation

\(\renewcommand{\AA}{\text{Å}}\)

# angle_style mm3 command

## Syntax

    angle_style mm3

## Examples

    angle_style mm3
    angle_coeff 1 100.0 107.0

## Description

The mm3 angle style uses the potential that is anharmonic in the angle as defined in (Allinger)

\[E = K (\theta - \theta_0)^2 \left[ 1 - 0.014(\theta - \theta_0) + 5.6(10)^{-5} (\theta - \theta_0)^2 - 7.0(10)^{-7} (\theta - \theta_0)^3 + 9(10)^{-10} (\theta - \theta_0)^4 \right]\]

where \(\theta_0\) is the equilibrium value of the angle, and \(K\) is a prefactor. The anharmonic prefactors have units \(\deg^{-n}\), for example \(-0.014 \deg^{-1}\), \(5.6 \cdot 10^{-5} \deg^{-2}\), …

The following coefficients must be defined for each angle type via the angle_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)

- \(\theta_0\) (degrees)

\(\theta_0\) is specified in degrees, but LAMMPS converts it to radians internally; hence \(K\) is effectively energy per radian^2.

## Restrictions

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

## Related commands

angle_coeff

## Default

none