Spin‐inversion mechanisms in O2 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 O2 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.

中文翻译：

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通过密度函数理论计算重新审视 O 2 与模型血红素复合物结合的自旋反转机制

使用密度泛函理论计算研究了 O2 与由 Fe(II)-卟啉和咪唑组成的模型血红素复合物结合的自旋反转机制。首先，我们应用最近提出的混合自旋哈密顿方法来定位不同总自旋多重性之间的自旋反转结构。成功地优化了九种自旋反转结构，用于单线态-三线态、单线态-五线态、三线态-五线态和五线态-七重态自旋反转过程。我们发现单重态-三重态自旋反转点位于势能面区域周围的 Fe-O 距离较短，而单重态-五重态和五重态-七重态自旋反转点位于较长的 Fe-O 距离处。这表明窄交叉和宽交叉模型在 O2 与 Fe-卟啉复合物的结合中都起作用。为了进一步了解自旋反转机制，我们进行了动态 Born-Oppenheimer 分子动力学计算。还讨论了与不同自旋多重性之间的自旋反转动力学相关的反应坐标。