class Potential:

    def __init__( self ):
        pass

class PairPotential:

    def __init__( self, alpha, b, c6, c8, f6, f8 ):
        self.alpha = alpha
        self.b     = b
        self.c6    = c6
        self.c8    = c8
        self.f6    = f6
        self.f8    = f8 
