Syntax:
angle_style cosine/shift/exp
Examples:
angle_style cosine/shift/exp angle_coeff * 10.0 45.0 2.0
Description:
The cosine/shift/exp angle style uses the potential
where Umin, theta, and a are defined for each angle 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. In this limit the potential reduces to the cosineshifted potential.
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:
Restrictions:
This angle 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:
angle_coeff, angle_cosineshift, dihedral_cosineshift
Default: none