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 MOFFF package. See the Build package doc page for more info.