angle_style cosine/buck6d command
angle_style cosine/buck6d angle_coeff 1 cosine/buck6d 1.978350 4 180.000000
The cosine/buck6d angle style uses the potential
where \(K\) is the energy constant, \(n\) is the periodic multiplicity and \(\theta_0\) is the equilibrium angle.
The 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 in the following order:
\(\theta_0\) is specified in degrees, but LAMMPS converts it to radians internally.
Additional to the cosine term the cosine/buck6d angle style computes the short range (vdW) interaction belonging to the pair_style buck6d between the end atoms of the angle. For this reason this angle style only works in combination with the pair_style buck6d styles and needs the special_bonds 1-3 interactions to be weighted 0.0 to prevent double counting.
This angle style can only be used if LAMMPS was built with the USER-MOFFF package. See the Build package doc page for more info.