I was under the impression that differences between the various long range electrostatic algorithms, ewald, PME, PPPM, to name a few, lied solely in their treatment of the reciprocal space term. Specifically, I thought all methods looped over a particles neighbor and summed q(i)*q(j)erfc(alphar)/r for the real space calculation. However, this is my impression, which I have yet to validate with others. I became confused when I recently read "Ewald summation techniques in perspective: a survey" whose equation 22 seems to have suggested a different way to calculate the short range potential. Could anyone else chime in here, and either tell me where I am wrong, or I am correct?