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

Ten low-lying electronic states of Fe(II) porphine, (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 multiconfigurational second-order perturbation (CASPT2) calculations with complete active space self-consistent field (CASSCF) reference functions with larger active space and basis sets. The enlargement of active space and basis sets has no influence on the conclusion of a previous multireference Moller-Plesset perturbation (MRMP) study. The present CASPT2 calculation concludes that the (5)A(1g) state is the ground state. A relativistic correction has been performed by the relativistic scheme of eliminating small components (RESC). For energetics, no significant contribution from the relativistic correction was found. The relative energies and orbital energies are not changed appreciably by the introduction of a relativistic correction. The present result does not agree with all the spectroscopic observations, but is consistent with a magnetic moment study. (C) 1999 American Institute of Physics. [S0021-9606(99)30233-6].