Some remarks on the calculation and use of retarded and static dipole sums in molecular exciton theory

Retardation corrections to the static dipole sums used in molecular exciton theory are calculated by an Ewald summation procedure. The corrections are found to be negligible thereby confirming conclusions of several earlier investigations. A description is given of the correct method of using retarded dipole sums in molecular exciton theory and some of the misuses pointed out. The widespread abuse of static dipole sums in molecular exciton theory is discussed and attributed to a misunderstanding of the k=0 selection rule and the shape dependence of static dipole sums.