LOCAL QUANTUM-CHEMISTRY - IMPLEMENTATION OF THE LOCAL SPACE APPROXIMATION AT THE AB-INITIO HARTREE-FOCK LEVEL

The local space approximation (LSA) method for embedding a finite clus ter into its surroundings is implemented at the ab initio restricted H artree-Fock level of theory. Our procedures for handling the initial c ombination of fragments in a way that takes full account of overlaps, and for obtaining the transformed two-electron integrals used in the l ocal space self-consistent field (SCF) treatment, are presented in det ail. Preliminary tests on small systems give results similar to those obtained in previous semiempirical calculations; in every case, the sm allest physically meaningful local space yields an energy within about 1 kcal/mol of the ''exact'' full space value.