Each of the bond interaction classes defines a potential 
as a function of the separation 
between a pair of covalently bonded atoms. Each bond is assigned a bond type index, and different values of the parameters in the bond potential function are used for different bond types.
All of the bond interaction classes implement a common interfaces, which is described here.
Bond Interaction Classes
- HarmonicBond - harmonic bond
- HarmonicL0Bond - harmonic bond with zero rest length (i.e., a Gaussian spring)
- FeneBond - finitely extensible bond
