Syntax:
dihedral_style cosine/shift/exp
Examples:
dihedral_style cosine/shift/exp dihedral_coeff 1 10.0 45.0 2.0
Description:
The cosine/shift/exp dihedral style uses the potential
where Umin, theta, and a are defined for each dihedral type.
The potential is bounded between [-Umin:0] and the minimum is located at the angle theta0. The a parameter can be both positive or negative and is used to control the spring constant at the equilibrium.
The spring constant is given by k=a exp(a) Umin/ [2 (Exp(a)-1)]. For a>3 k/Umin = a/2 to better than 5% relative error. For negative values of the a parameter, the spring constant is essentially zero, and anharmonic terms takes over. The potential is furthermore well behaved in the limit a->0, where it has been implemented to linear order in a for a < 0.001.
The following coefficients must be defined for each dihedral type via the dihedral_coeff command as in the example above, or in the data file or restart files read by the read_data or read_restart commands:
Restrictions:
This dihedral style can only be used if LAMMPS was built with the USER-MISC package. See the Making LAMMPS section for more info on packages.
Related commands:
dihedral_coeff, angle_cosineshiftexp
Default: none