Applications of fourier transforms in molecular orbital theory

Fourier transform methods introduced by Harris are applied to the evaluation of Frenkel exciton lattice sums. The slowly-convergent direct lattice sum is converted into a rapidly-convergent reciprocal lattice sum which includes all orders in the multipole expansion. A simple example is discussed, and the calculated exciton energy as a function of wave number is compared with the results of the Ewald method.