The CosineSqAngle interaction implements a potential that depends quadratically on the cosine $\cos(\theta)$ of the bend angle. The energy is given by

$V(\theta) = \frac{\kappa}{2} [ \cos(\theta) - \cos(\theta_0)]^{2}$

Different values are defined for the parameters $\kappa$ and $\theta_{0}$ for each angle type.

The parameter file format is:

kappa Array<float>

theta0 Array<float>

The kappa array is entered in column form, with one entry per line. The parameter theta0 is entered in degrees in the input file, but is then immediately converted to radians. The angle interaction parameter block for a system with two angle types (nAngleType=2) might thus look like:

kappa     50.0
          40.0
theta0    81.0
          81.0

where $ $\theta_{0}$ is 81 degrees for both angle types.