A HYBRID METHOD FOR THE EVALUATION OF THE MATRIX-ELEMENTS OF THE COULOMB POTENTIAL

An analysis of the method of obtaining matrix elements of the Coulomb potential by numerical integration of the 'exact' potential, a strateg y proposed by Termath and Handy, reveals that this method will be inac curate in large systems because of the long-range nature of the Coulom b forces. The results can be improved substantially if one integrates the long-range part of the potential analytically. This has been achie ved - at virtually no extra cost - by introducing a simple model densi ty whose electrostatic potential has the correct long-range behaviour and whose Coulomb matrix elements can easily be evaluated analytically . The model density can be designed to reduce errors which arise in th e fully numerical method due to the electrostatic potential in the cor es of heavy atoms.