A GSO–HDFT study of noncollinear spin structures of [2Fe–2S] cluster

Abstract

The electronic and spin structures of a [2Fe–2S] model complex: Fe 2 S 2 ( SH ) 4 3 - ( 1), were investigated by hybrid density functional theory (HDFT) calculations. Generalized spin orbital (GSO) approach has been examined to investigate the delocalization nature at the reduced form. The calculated results showed that the delocalization is largely dependent on the geometrical [2Fe–2S] core structure. At the symmetrical geometry, the GSO solution was a mixed-valence state: Fe 2.5+Fe 2.5+, with a noncollinear spin state. The energy difference between the GSO solution and an unrestricted state was extremely small (4 cm −1). On the other hand at the asymmetrical geometry, the GSO solution converged into a trapped valence state: Fe 3+Fe 2+ with a collinear spin state, which was almost the same as an unrestricted result. Natural orbital analysis was performed to elucidate the magnetic orbital interactions at the GSO and unrestricted solutions. These results indicated that the delocalization of the odd electron is largely suppressed for the strong antiferromagnetic interactions between two irons. In conclusion, the GSO descriptions were not drastically improved the ground state energies of the [2Fe–2S] cluster, however, the GSO approach has opened to investigate a variety of electronic structures in the mixed valence states, which could not be investigated by a broken symmetry (BS) approach.