Comparison of Hartree-Fock and Kohn-Sham Determinants as Wave Functions

Abstract

Kohn-Sham (KS) and Hartree-Fock (HF) determinants were used as the true many-body wave functions for calculations of molecular energies, vibrational frequencies, and excited electronic states. The results justified common practice, encountered in the sum over states theories, in which these two determinants are used as the first-order approximation of the wave function. However, a distinct behavior with respect to the second-order perturbation calculation was observed for the two cases. The Raleigh-Schrödinger perturbation theory, which is formally identical to the Levy-Görling formalism and analogous to the usual HF/Møller-Plesset approach, leads to rather discouraging results for the KS determinant. On the other hand, the rigid KS orbitals are more suitable for modeling of excited electronic states, which was indicated by the obtained transition energies for model molecules. © 2000 John Wiley & Sons, Inc.