Theoretical foundations of purely semi-empirical quantum chemistry. II. Molecular properties

Abstract

Explicit expressions are presented enabling the ab initio evaluation of the true effective operators for molecular properties that are customarily only empirically determined in purely semi-empirical quantum chemical theories of molecular electronic structure. These true effective operators are obtained under the condition that they reproduce exact expectation values and transition matrix elements when used in conjunction with the eigenfunctions of the true effective valence shell hamiltonian which operates solely in the space spanned by a minimum basis set of valence shell orbitals. Properties of these true effective operators and the methods currently available for their computation from first principles are briefly discussed.