Open-shell localized Hartree–Fock approach for an efficient effective exact-exchange Kohn–Sham treatment of open-shell atoms and molecules

Abstract

Within the framework of the symmetrized Kohn–Sham (KS) formalism an effective exact-exchange approach, the open-shell localized Hartree–Fock (OSLHF) method, is derived. The derivation relies on an approximation of energy denominators in KS one-particle Greens functions, the approximation of average magnitudes of eigenvalue differences, which is introduced. With the OSLHF method open-shell molecules can be treated efficiently and numerically stable without running into the symmetry problem encountered in conventional KS methods. The self-interaction free Hamiltonian operator of the OSLHF approach is in all cases non-spin-polarized and exhibits the full molecular point group symmetry in real space. Results for atoms as well as small and medium size molecules are presented. A procedure is introduced which yields special basis sets required for an efficient construction of the Slater potential which enters the effective KS potential of localized Hartree–Fock methods.