ANALYTIC LOWDIN ALPHA-FUNCTION METHOD FOR 2-CENTER ELECTRON-REPULSION INTEGRALS OVER SLATER-TYPE ORBITALS

Using the Lowdin alpha-function method in which displaced orbitals are expanded in spherical harmonics, two-center, two-electron repulsion integrals of the Coulomb, hybrid, and exchange type are done analytically using Slater-type orbitals. Computer algebra and integer arithmetic are used to obtain analytic results and avoid cancellation errors by the generation of rational matrix elements for C, E, and F matrices that are used to express the alpha-function. The formula for the exchange integral is kept simple by reversing the order of integration over each part of a split quadrant. Only two basic integrals are used that are first efficiently evaluated by using look-up tables and then used repeatedly.