Multipole Ewald sums for the fast multipole method

A generalized Ewald summation for electric multipoles in periodic arrays is presented in the form needed for multipole transformations used in the fast multipole method. In the fast multipole method the time-consuming Ewald sums are thus eliminated in favor of a simple matrix transformation with almost no computational cost. The derivation also applies to traditional electrostatic potential calculations in periodic charged systems. A summary computational prescription is provided.