Correlated Ab Initio and Density Functional Studies on H2 Activation by FeO(.).

The reaction FeO+ + H2 → Fe+ + H2O is a simple model for hydrogen abstraction processes in biologically important heme systems. The geometries of all relevant stationary points on the lowest sextet and quartet surfaces were optimized using several density functionals as well as the CASSCF method. The corresponding energy profiles were computed at the following levels: density functional theory using gradient-corrected, hybrid, meta, hybrid-meta, and perturbatively corrected double hybrid functionals; single-reference coupled cluster theory including up to single, double, triple, and perturbative quadruple excitations [CCSDT(Q)]; correlated multireference ab initio methods (MRCI, MRAQCC, SORCI, SORCP, MRMP2, NEVPT2, and CASPT2). The calculated energies were corrected for scalar relativistic effects, zero-point vibrational energies, and core–valence correlation effects. MRCI and SORCI energies were corrected for size-consistency errors using an a posteriori Davidson correction (+Q) leading to MRCI+Q and SOR...