Theoretical study of the electronic ground state of iron(II) porphine

Abstract

Ten low-lying electronic states of Fe(II)-porphine, the 5 A 1 g , 5 E g , 5 B 2 g , 3 A 2 g , 3 B 2 g , 3 E g ( A) , 3 E g ( B) , 1 A 1 g , 1 B 2 g and 1 E g states, are studied with multireference Møller–Plesset perturbation theory with complete active space self-consistent field (CASSCF) reference functions. Triplet and singlet states are significantly multiconfigurational in character. The ten low-lying states are computed to be within a 2 eV span and the 5 A 1 g state is predicted to be the lowest. At the CASSCF level, all the quintet states are lower in energy than the triplets. This tendency is reversed, except for the 5 A 1 g state, after perturbation theory is applied. Among controversial candidates for the triplet ground state, the 3 E g state is computed to be more stable, by 0.18∼0.23 eV, than the 3 A 2 g and 3 B 2 g states.