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 cluster into its surroundings is implemented at the ab initio restricted Hartree-Fock level of theory. Our procedures for handling the initial combination of fragments in a way that takes full account of overlaps, and for obtaining the transformed two-electron integrals used in the local space self-consistent field (SCF) treatment, are presented in detail. Preliminary tests on small systems give results similar to those obtained in previous semiempirical calculations; in every case, the smallest physically meaningful local space yields an energy within about 1 kcal/mol of the ''exact'' full space value.