Semianalytic Method for Four-Center Molecular Integrals Over Slater-Type Orbitals

摘要

A strategy for the evaluation of four-center molecular integrals over Slater-typeorbitals is developed using the Lowdin a-function approach in which displaced orbitals are expanded in spherical harmonies. The harmonic potentials are produced analytically and evaluated along a grid, The harmonic charge distributions are given an analytical formulation and are evaluated over the common grid, and the numerical integrations are performed for each harmonic. Using an example with ls orbitals, only nine harmonies are needed for good results. Computer algebra and integer arithmetic are used to generate C, E, and F matrices that are stored as part of the data base. One-dimensional T and X matrices are introduced as an aid in computation. The employment of look-up tables and vector and parallel processing promises to make this method, which can generalized, practical.