Interplay of Correlation and Relativistic Effects in Correlated Calculations on Transition-Metal Complexes: The (Cu2O2)2+ Core Revisited
Interplay of Correlation and Relativistic Effects in Correlated Calculations on Transition-Metal Complexes: The (Cu2O2)2+ Core Revisited
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DOI：
10.1021/ct1006949
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发表时间：
2011-05-01
影响因子：
5.5
通讯作者：
Neese, Frank
中科院分区：
文献类型：
--
作者：
Liakos, Dimitrios G.;Neese, Frank
由于大规模计算设备的出现和高效新算法的发展，基于波函数的从头计算在生物无机化学中变得越来越普遍。原则上，它们提供了一条通往高精度的系统路线。然而，这些计算绝非微不足道。本文通过对[{Cu（C2 H8 N2）}（2）O-2]（2+）配合物的过氧-和双-（μ-oxo）异构体之间的平衡进行系统的理论研究，提出了一些相关的观点。虽然这个系统通常被认为是一个典型的多参考的情况下，我们对待它的单参考本地对自然轨道耦合集群方法，并重申，在这个系统中的多参考字符是非常有限的。一组中间结构，为两种异构体之间的相互转化，计算通过松弛的表面扫描，从而允许计算的能量分布，干净地连接双-（μ-氧代）和侧上过氧最小的基态势能表面。只有在最高水平的理论，涉及完整的基组外推，三重激发的贡献，以及相对论和溶剂效应，双-（μ-氧代）异构体被发现是稍微更稳定的过氧结构。这与实验结果一致。详细分析了基组、三重激发、相对论、溶剂贡献等因素对体系的影响。最后，从头计算结果进行了比较，密度泛函计算使用各种泛函。它表明，在文献中报道的结果的差异的最大部分是由于不一致的相对论效应，这是大的从头算和密度泛函理论计算的处理。
Owing to the availability of large-scale computing facilities and the development of efficient new algorithms, wave function-based ab initio calculations are becoming more common in bioinorganic chemistry. In principle they offer a systematic route toward high accuracy. However, these calculations are by no means trivial. In this contribution we address some pertinent points through a systematic theoretical study for the equilibrium between the peroxo- and bis-(mu-oxo) isomers of the [{Cu(C2H8N2)}(2)O-2](2+) complex. While this system is often regarded as a prototypical multireference case, we treat it with the single reference local-pair natural orbital coupled cluster method and reiterate that the multireference character in this system is very limited. A set of intermediate structures, for the interconversion between the two isomers, is calculated through a relaxed surface scan thus allowing the calculation of an energetic profile that cleanly connects the bis-(mu-oxo) and side-on peroxo minima on the ground-state potential energy surface. Only at the highest level of theory involving complete basis set extrapolation, triple excitation contributions as well as relativistic and solvent effects, the bis-(mu-oxo) isomer is found to be slightly more stable than the peroxo structure. This is in agreement with the experimental findings. The effects of basis set, triples excitation, relativity, and solvent contribution have all been analyzed in detail. Finally, the ab initio results are compared with density functional calculations using various functionals. It is demonstrated that the largest part of the discrepancies of the results reported in the literature are due to an inconsistent handling of relativistic effects, which are large in both ab initio and density functional theory calculations.