FeP(Im)-AB Bonding Energies Evaluated with A Large Number of Density Functionals (P = porphine, Im = imidazole, AB = CO, NO, and O(2)).

Sixty-four (64) density functionals, ranging from GGA, meta-GGA, hybrid GGA to hybrid meta-GGA, were tested to evaluate the FeP(Im)-AB bonding energies (E(bond)) in the heme model complexes FeP(Im)(AB) (P = porphine, Im = imidazole, AB = CO, NO, and O(2)). The results indicate that an accurate prediction of E(bond) for the various ligands to heme is difficult with the DFT methods; usually a functional successful for one system does not perform equally well for the other system(s). Relatively satisfactory results for the various FeP(Im)-AB bonding energies are obtained with the meta-GGA funtionals BLAP3 and Bmτ1; they yield E(bond) values of ca.1.1, 1.2, and 0.4 eV for AB = CO, NO, and O(2), respectively, which are in reasonable agreement with experimental data (0.78 - 0.85 eV for CO, 0.99 eV for NO, and 0.44 - 0.53 eV for O(2)). The other functionals show more or less deficiency for one or two of the systems. The performances of the various functionals in describing the spin-state energetics of the five-coordinate FeP(Im) complex were also examined.