Spin-inversion mechanisms in O 2 binding to a model heme complex revisited by density function theory calculations

• Published in: Journal of computational chemistry Vol. 41; no. 11; pp. 1130 - 1138
• Main Authors: Saito, Kohei, Watabe, Yuya, Fujihara, Takashi, Takayanagi, Toshiyuki, Hasegawa, Jun-Ya
• Format: Journal Article
• Language: English
• Published: United States 30.04.2020
• Subjects: spin crossover; spin inversion; spin-forbidden
• ISSN: 0192-8651; 1096-987X
• DOI: 10.1002/jcc.26159

Spin-inversion mechanisms in O binding to a model heme complex, consisting of Fe(II)-porphyrin and imidazole, were investigated using density-functional theory calculations. First, we applied the recently proposed mixed-spin Hamiltonian method to locate spin-inversion structures between different total spin multiplicities. Nine spin-inversion structures were successfully optimized for the singlet-triplet, singlet-quintet, triplet-quintet, and quintet-septet spin-inversion processes. We found that the singlet-triplet spin-inversion points are located around the potential energy surface region at short Fe-O distances, whereas the singlet-quintet and quintet-septet spin-inversion points are located at longer Fe-O distances. This suggests that both narrow and broad crossing models play roles in O binding to the Fe-porphyrin complex. To further understand spin-inversion mechanisms, we performed on-the-fly Born-Oppenheimer molecular dynamics calculations. The reaction coordinates, which are correlated to the spin-inversion dynamics between different spin multiplicities, are also discussed.