Cramer Christopher J, Włoch Marta, Piecuch Piotr, Puzzarini Cristina, Gagliardi Laura
Department of Chemistry and Supercomputer Institute, University of Minnesota, 207 Pleasant St. SE, Minneapolis, Minnesota 55455, USA.
J Phys Chem A. 2006 Feb 9;110(5):1991-2004. doi: 10.1021/jp056791e.
Accurately describing the relative energetics of alternative bis(mu-oxo) and mu-eta2:eta2 peroxo isomers of Cu2O2 cores supported by 0, 2, 4, and 6 ammonia ligands is remarkably challenging for a wide variety of theoretical models, primarily owing to the difficulty of maintaining a balanced description of rapidly changing dynamical and nondynamical electron correlation effects and a varying degree of biradical character along the isomerization coordinate. The completely renormalized coupled-cluster level of theory including triple excitations and extremely efficient pure density functional levels of theory quantitatively agree with one another and also agree qualitatively with experimental results for Cu2O2 cores supported by analogous but larger ligands. Standard coupled-cluster methods, such as CCSD(T), are in most cases considerably less accurate and exhibit poor convergence in predicted relative energies. Hybrid density functionals significantly underestimate the stability of the bis(mu-oxo) form, with the magnitude of the error being directly proportional to the percentage Hartree-Fock exchange in the functional. Single-root CASPT2 multireference second-order perturbation theory, by contrast, significantly overestimates the stability of bis(mu-oxo) isomers. Implications of these results for modeling the mechanism of C-H bond activation by supported Cu2O2 cores, like that found in the active site of oxytyrosinase, are discussed.
准确描述由0、2、4和6个氨配体支撑的Cu2O2核的替代双（μ-氧代）和μ-η2:η2过氧异构体的相对能量，对于各种各样的理论模型来说都是极具挑战性的，主要是因为难以对快速变化的动态和非动态电子相关效应以及沿异构化坐标变化程度不同的双自由基特征进行平衡描述。包括三重激发的完全重整化耦合簇理论水平和极其高效的纯密度泛函理论水平在定量上相互一致，并且在定性上也与由类似但更大的配体支撑的Cu2O2核的实验结果一致。标准的耦合簇方法，如CCSD(T)，在大多数情况下准确性要低得多，并且在预测相对能量时收敛性较差。杂化密度泛函显著低估了双（μ-氧代）形式的稳定性，误差大小与泛函中哈特里-福克交换的百分比成正比。相比之下，单根CASPT2多参考二阶微扰理论显著高估了双（μ-氧代）异构体的稳定性。讨论了这些结果对模拟由支撑的Cu2O2核（如在氧酪氨酸酶活性位点中发现的那样）激活C-H键机制的影响。
