Electronic Structure, Spin-States, and Spin-Crossover Reaction of Heme-Related Fe-Porphyrins: A Theoretical Perspective
2012 (English)In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 116, no 20, 5849-5859 p.Article in journal (Refereed) Published
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 but electronic structurally complicated system tetra-coordinated planar Fe porphyrin in comparison to the penta-coordinated systems. This analysis explains the observed paradoxical appearance of certain peaks in the local density of states (DOS).
Place, publisher, year, edition, pages
2012. Vol. 116, no 20, 5849-5859 p.
IdentifiersURN: urn:nbn:se:uu:diva-253290DOI: 10.1021/jp3021563ISI: 000304338300006PubMedID: 22512398OAI: oai:DiVA.org:uu-253290DiVA: diva2:813991