def __init__(self, scaling, strengths, coordinates=None):
PairFF.__init__(self, scaling, coordinates)<EOL>self.strengths = strengths<EOL>
Initialize a DispersionFF object

           Arguments:
             scaling  --  symmetric NxN array with pairwise scaling factors.
                          When an element is set to zero, it will be excluded.
             strengths  --  a symmetric with linear coefficients in front of
                            r**-6 for each atom pair

           Optional arguments:
             coordinates  --  the initial Cartesian coordinates of the system,
                              which can be updated with the update_coordinates
                              method