$$

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)

$$E=K(\theta -{\theta }_0{)}^2[1-0.014(\theta -{\theta }_0)+5.6(10{)}^{-5}(\theta -{\theta }_0{)}^2-7.0(10{)}^{-7}(\theta -{\theta }_0{)}^3+9(10{)}^{-10}(\theta -{\theta }_0{)}^4]$$

where ${\theta }_0$ is the equilibrium value of the angle, and $K$ is a prefactor. The anharmonic prefactors have units ${\mathrm{deg}}^{-n}$, for example $-0.014{\mathrm{deg}}^{-1}$, $5.6\cdot {10}^{-5}{\mathrm{deg}}^{-2}$, …

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