angle_style mm3 command
angle_style mm3 angle_coeff 1 100.0 107.0
The mm3 angle style uses the potential that is anharmonic in the angle as defined in (Allinger)
where theta0 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(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:
Theta0 is specified in degrees, but LAMMPS converts it to radians internally; hence the units of K are in energy/radian^2.
This angle style can only be used if LAMMPS was built with the USER_YAFF package. See the Build package doc page for more info.