SEMI-CANONICAL MO IN THE VARIED OPEN SHELL METHOD AND RELATED APPROACHES
A. V. Luzanov
Institute for Single Crystals, National Academy of Sciences of Ukrainian, Kharkov
Keywords: restricted Hartree-Fock method, Roothaan theory, canonical MOs, Koopmans theorem, Aufbau principle
Abstract
The self-consistency schemes previously developed in J. Struct. Chem ., 30, N 5, p. 3 (1986) are shown to belong to the class of semi-canonical orbital schemes. In the derivation they explicitly involve only a part of canonical Koopmans orbitals in the iteration process. In particular, within the restricted Hartree-Fock method for a non-degenerate case a semi-canonical variational scheme based on the matrix elements of the unrestricted Hartree-Fock method is studied. Errors present in the above mentioned work in the description of the scheme of a varied open shell are corrected. A possible generalization for the case of Roothaan type degeneration is proposed and specific examples of low-spin and high-spin states with a violated Aufbau filling principle are considered.
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