$$\renewcommand{\AA}{\text{Å}}$$

# angle_style mm3 command¶

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.

none