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

Ten low-lying electronic states of Fe(II)-porphine, the (5)A(1g), E-5(g), B-5(2g), (3)A(2g), B-3(2g), E-3(g)(A), E-3(g)(B), (1)A(1g), B-1(2g) and E-1(g) states, are studied with multireference Moler-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(1g) 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(1g) state, after perturbation theory is applied. Among controversial candidates for the triplet ground state, the E-3(g) State is computed to be more stable, by 0.18 similar to 0.23 eV, than the (3)A(2g) and B-3(2g) states. (C) 1998 Elsevier Science B.V. All rights reserved.