计算化学的金属氢化物问题：起源与后果,The Journal of Physical Chemistry A

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计算化学的金属氢化物问题：起源与后果
The Journal of Physical Chemistry A ( IF 2.7 ) Pub Date : 2019-03-18 00:00:00 , DOI: 10.1021/acs.jpca.9b02367
Klaus A. Moltved ₁ , Kasper P. Kepp ₁

Affiliation

金属氢键的形成和断裂对于许多重要的催化过程至关重要，例如过渡金属催化的氨合成，加氢反应和水分解，因此，它们需要足够的理论描述。我们研究了3d，4d和5d过渡系列的所有30 M–H和30 M ⁺ –H键的数据集；这些系统中有50个具有实验已知的键解离焓（BDE）。为了探究低和高配位数的极限，我们还研究了19 ML _n的数据集H配合物。使用Hartree-Fock（HF），MP2，CCSD，CCSD（T）和10种不同的密度函数计算BDE，包括局部，GGA，混合GGA，元混合，范围分隔和双重混合。我们的十个最重要的发现如下：（1）HF由于缺乏静态相关性而无法完全描述金属氢键；（2）这使得诸如MP2甚至CCSD（T）之类的HF后方法比许多密度函数的性能更差；（3）DFT描述纯的M–H键比描述其他金属配体键（0–20％）需要更多的HF交换（平均约35％）；（4）我们设计了一个测试，通过将DFT误差与单电子SIE度量相关联来确定自相互作用误差（SIE）是否重要；（5）我们证明SIE与DFT错误直接相关，从而导致了大多数问题。（6）HF-DFT无法处理这些系统，因为HF方法在密度级别上已经太病理了；（7）相反，我们定义并应用一个简单的电子异常度量，作为在自洽PBE0和SVWN密度下计算出的PBE能量差，该度量给出了适当的扩展并有效地捕获了由密度引起的误差；（8）金属的低电负性会导致类似氢化物的电子密度增加，这使金属氢化物成为已经在平衡几何结构上表现出SIE的多电子系统的主要例子；（9）在协调饱和的ML中我们定义并应用一个简单的电子异常度量，作为在自洽PBE0和SVWN密度下计算出的PBE能量差，该度量给出了适当的分布并有效地捕获了密度派生的误差。（8）金属的低电负性会导致类似氢化物的电子密度增大，这使金属氢化物成为已经在平衡几何条件下表现出SIE的多电子系统的主要例子；（9）在协调饱和的ML中我们定义并应用一个简单的电子异常度量，作为在自洽PBE0和SVWN密度下计算出的PBE能量差，该度量给出了适当的分布并有效地捕获了密度派生的误差。（8）金属的低电负性会导致类似氢化物的电子密度增加，这使金属氢化物成为已经在平衡几何结构上表现出SIE的多电子系统的主要例子；（9）在协调饱和的ML中_n H系统，所需的HF交换少得多；也就是说，HF交换要求随协调数而变化很大。因此，对于涉及MH键和ML键以及配位数不断变化的任何催化过程，DFT都是不平衡的。（10）重要的是，单独的范围分隔和双混合功能CAM-B3LYP和B2PLYP在M–H和M–L系统中以及在低和高配位数以及至少CCSD方面均表现良好（T）。这给希望以真实催化反应所需的平衡配位数对所有类型的M-L键的计算化学进行平衡处理的希望。

"点击查看英文标题和摘要"

The Metal Hydride Problem of Computational Chemistry: Origins and Consequences

Formation and breaking of metal–hydrogen bonds are central to many important catalytic processes such as transition-metal catalyzed ammonia synthesis, hydrogenation reactions, and water splitting, and thus, they require an adequate theoretical description. We studied a data set of all 30 M–H and 30 M⁺–H bonds of the 3d, 4d, and 5d transition series; 50 of these systems have experimentally known bond dissociation enthalpies (BDE). To probe both the limit of low and high coordination number, we also studied a data set of 19 ML_nH complexes. The BDEs were computed using Hartree–Fock (HF), MP2, CCSD, CCSD(T), and 10 diverse density functionals including local, GGA, hybrid GGA, meta hybrid, range-separated, and double hybrids. Our ten most important findings are as follows: (1) HF fails completely to describe the metal hydrogen bond due to its lack of static correlation; (2) this makes post-HF methods such as MP2 and even CCSD(T) perform worse than many density functionals; (3) DFT requires much more HF exchange (∼35% on average) to describe the pure M–H bonds than to describe other metal ligand bonds (0–20%); (4) we design a test to determine if self-interaction error (SIE) is important by correlating DFT errors against a one-electron SIE metric; (5) we show that SIE correlates directly with the DFT errors and thus causes most of the problem; (6) HF-DFT cannot handle these systems because the HF method is too pathological already at the density level; (7) instead, we define and apply a simple metric of electronic abnormality as the difference in PBE energy computed at the self-consistent PBE0 and SVWN densities, and this metric gives appropriate spread and effectively captures density-derived errors; (8) the low electronegativity of the metal enforces a diffuse hydride-like electron density, which make the metal hydrides primary examples of many-electron systems exhibiting SIE already at equilibrium geometries; (9) in the coordinatively saturated ML_nH systems, much less HF exchange is required; i.e., the HF exchange requirements vary drastically with coordination number. Accordingly, DFT is unbalanced for any catalytic process involving both M–H and M–L bonds and changing coordination numbers; (10) importantly, the range-separated and double-hybrid functionals CAM-B3LYP and B2PLYP alone perform well for both M–H and M–L systems and in both limits of low and high coordination number, and at least as well as CCSD(T). This lends hope to a balanced treatment of computational chemistry for all types of M–L bonds at variable coordination number, as required for real catalytic reactions.

更新日期：2019-03-18

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