def yield_pair_energies(self, index1, index2):
A = self.As[index1, index2]<EOL>B = self.Bs[index1, index2]<EOL>distance = self.distances[index1, index2]<EOL>yield A*np.exp(-B*distance), <NUM_LIT:1><EOL>
Yields pairs ((s(r_ij), v(bar{r}_ij))