FeP(Im)-AB bonding energies evaluated with a large number of density functionals (P = porphine, Im = imidazole, AB = CO, NO, and O2)

Sixty-four 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 other system(s). Relatively satisfactory results for the various FeP(Im)-AB bonding energies are obtained with the meta-GGA functionals BLAP3 and Bm tau 1; 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.