EXTENSION OF THE MNDO FORMALISM TO D-ORBITALS - INTEGRAL APPROXIMATIONS AND PRELIMINARY NUMERICAL RESULTS

The point charge model for calculating the two-center two-electron integrals in MNDO and related methods is extended to d orbitals. It is suggested to expand these integrals in terms of semiempirical multipole-multipole interactions where all monopoles, dipoles and quadrupoles are included, and all higher multipoles are neglected. The proposed scheme has been implemented, and numerical results for the integrals are reported. A preliminary MNDO parametrization for chlorine indicates that the inclusion of d orbitals improves the results significantly, compared with the original MNDO and related methods.