Kurashige Yuki, Saitow Masaaki, Chalupský Jakub, Yanai Takeshi
Department of Theoretical and Computational Molecular Science, Institute for Molecular Science, Okazaki, Aichi 444-8585, Japan.
Phys Chem Chem Phys. 2014 Jun 28;16(24):11988-99. doi: 10.1039/c3cp55225j.
The O-O (oxygen-oxygen) bond formation is widely recognized as a key step of the catalytic reaction of dioxygen evolution from water. Recently, the water oxidation catalyzed by potassium ferrate (K2FeO4) was investigated on the basis of experimental kinetic isotope effect analysis assisted by density functional calculations, revealing the intramolecular oxo-coupling mechanism within a di-iron(vi) intermediate, or diferrate [Sarma et al., J. Am. Chem. Soc., 2012, 134, 15371]. Here, we report a detailed examination of this diferrate-mediated O-O bond formation using scalable multireference electronic structure theory. High-dimensional correlated many-electron wave functions beyond the one-electron picture were computed using the ab initio density matrix renormalization group (DMRG) method along the O-O bond formation pathway. The necessity of using large active space arises from the description of complex electronic interactions and varying redox states both associated with two-center antiferromagnetic multivalent iron-oxo coupling. Dynamic correlation effects on top of the active space DMRG wave functions were additively accounted for by complete active space second-order perturbation (CASPT2) and multireference configuration interaction (MRCI) based methods, which were recently introduced by our group. These multireference methods were capable of handling the double shell effects in the extended active space treatment. The calculations with an active space of 36 electrons in 32 orbitals, which is far over conventional limitation, provide a quantitatively reliable prediction of potential energy profiles and confirmed the viability of the direct oxo coupling. The bonding nature of Fe-O and dual bonding character of O-O are discussed using natural orbitals.
氧-氧（O-O）键的形成被广泛认为是水氧化生成氧气催化反应的关键步骤。最近，基于密度泛函计算辅助的实验动力学同位素效应分析，对高铁酸钾（K2FeO4）催化的水氧化反应进行了研究，揭示了二价铁（VI）中间体或高铁酸盐内的分子内氧偶联机制[萨尔马等人，《美国化学会志》，2012年，134卷，15371页]。在此，我们报告使用可扩展多参考电子结构理论对这种高铁酸盐介导的O-O键形成进行的详细研究。沿着O-O键形成途径，使用从头算密度矩阵重整化群（DMRG）方法计算了超越单电子图像的高维相关多电子波函数。使用大活性空间的必要性源于对与双中心反铁磁多价铁-氧偶联相关的复杂电子相互作用和变化的氧化还原状态的描述。我们小组最近引入的基于完全活性空间二阶微扰（CASPT2）和多参考组态相互作用（MRCI）的方法，在活性空间DMRG波函数之上累加考虑了动态相关效应。这些多参考方法能够处理扩展活性空间处理中的双壳层效应。在32个轨道中包含36个电子的活性空间的计算，远远超出了传统限制，对势能面提供了定量可靠的预测，并证实了直接氧偶联的可行性。使用自然轨道讨论了Fe-O的键合性质和O-O的双重键合特征。
