铁卟啉02.pdf

Article

Electronic Structure, Spin-States, and Spin-Crossover Reaction of
Heme-Related Fe-Porphyrins: A Theoretical Perspective
Md. Ehesan Ali*
Centre for Theoretical Chemistry, Ruhr-Universitat,̈ D-44780 Bochum, Germany
Biplab Sanyal and Peter M. Oppeneer
Department of Physics and Astronomy, Uppsala University, Box 516, S-751 20 Uppsala, Sweden
ABSTRACT: The electronic structures, spin-states, and geometrical parameters
of tetra-, penta-, and hexa-coordinated iron-porphyrins are investigated applying
density functional theory (DFT) based calculations, utilizing the plane-wave
pseudopotential as well as localized basis set approaches. The splitting of the spin
multiplet energies are investigated applying various functionals including recently
developed hybrid meta-GGA (M06 family) functionals. Almost all of the hybrid
functionals accurately reproduce the experimental ground state spins of the
investigated Fe-porphyrins. However, the energetic ordering of the spin-states
and the energies between them are still an issue. The widely used B3LYP
provides consistent results for all chosen systems. The GGA+U functionals are
found to be equally competent. After assessing the performance of various functionals in spin-state calculations, the potential
energy surfaces of the oxygen binding process by heme is investigated. This reveals a “double spin-crossover” feature for the
lowest energy reaction path that is consistent with previous CASPT2 calculations but predicting a lowest energy singlet state. The
calculations have hence captured the spin-crossover as well as spin-flip processes. These are driven by the intra-atomic orbital
polarization on the central metal atom due to the atomic and orbitals rearrangements. The nature of the chemical bonding and a
molecular orbital analysis are also performed for the geometrically simple