ASSESSMENT OF SOME RECENTLY DEVELOPED DENSITY FUNCTIONALS FOR CALCULATIONS ON IRON PORPHYRINS

Abstract

The behaviors of several recently developed density functionals (M05, M05-2x, M06, M06-2x, M06-L, KT1, KT2) in describing the spin-state energetics of iron porphyrins [ FeP , FeP ( Cl ), FeP ( THF )2, FeTpivPP ] have been investigated, where KT1 and KT2 are pure GGA (generalized gradient approximation) functionals; M06-L is a meta-GGA functional that contains the kinetic-energy density τ[=∑(∇ϕi)2]; M05, M05-2x, M06, and M06-2x are hybrid meta-GGA functionals that include both the kinetic-energy density and Hartree–Fock exchange. The results reveal that KT1 and KT2 are biased toward lower-spin states and so fail to give the correct ground state for the high-spin systems, but KT2 shows a significant improvement over KT1. M05, M05-2x, M06, and M06-2x yield results which are in qualitative agreement with the experimental findings for FeP ( Cl ) and FeP ( THF )2, but their relative energies for the high-spin states are actually underestimated greatly. Among the various functionals tested here, only M06-L is able to provide a satisfactory description of the energetics of FeP , FeP ( Cl ), and FeP ( THF )2, for which the ground-state multiplicities are surely known. FeTpivPP is predicted to be high spin by the M06-L functional, in agreement with the early experimental magnetic measurement, but different from the previous results (and conclusion) obtained with other various functionals.