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首页> 外文期刊>Dalton transactions: An international journal of inorganic chemistry >Does DFT-D estimate accurate energies for the binding of ligands to metal complexes?
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Does DFT-D estimate accurate energies for the binding of ligands to metal complexes?

机译：DFT-D是否能估计配体与金属络合物结合的准确能量？

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We have studied the homolytic dissociation of a methyl radical from a model of methyl cobalamin. For this reaction, density functional theory with an atom-pairwise dispersion correction (DFT-D) gives a dispersion contribution to the bond dissociation energy (BDE) of 22-51 kJ mol~(-1) depending on the functional, i.e. much more than common estimates for the total dispersion interaction energy of the methyl group in typical solvents. We show that this large energy correction results from many rather small (0-2 kJ mol~(-1)) interactions that arise between the ligand and the metal and the other ligands when a short metal-ligand bond is formed. The energy terms result mostly from atom pairs connected by two or three bonds, i.e. terms that normally are ignored or scaled down at the molecular mechanics level, and have large contributions from r~(-8) terms. The added dispersion energy diminishes the variation in the calculated BDE observed among various generalised-gradient approximation (GGA) functionals, whereas a gap still persists between the results of GGA and hybrid functionals. Model calculations at the local MP2 and CCSD (second-order perturbation theory and coupled cluster theory with single and double excitations) levels are in a similar range as the dispersion interactions estimated by DFT-D (23-29 kJ mol~(-1)). However, both the DFT-D and the wavefunction-based results include middle-range correlation effects that vary greatly between different DFT methods owing to their different density-based description in the short-range regime. Therefore, it is not meaningful to discuss which DFT method gives the most accurate estimate of the dispersion contribution to the BDE. Moreover, for a balanced treatment of dispersion during the binding reaction in solution, the dispersion energy of the ligand and the unbound complex with the surroundings needs also to be considered, which decreases the net dispersion contribution to binding by ～20 kJ mol~(-1).
机译：我们已经研究了甲基钴胺素模型的甲基自由基的均相解离。对于该反应，取决于功能的密度泛函理论（具有原子对色散校正（DFT-D））对键离解能（BDE）的色散贡献为22-51 kJ mol〜（-1），即更大。比通常估算的甲基在典型溶剂中的总分散体相互作用能高。我们表明，这种大的能量校正是由于当形成短的金属-配体键时，在配体与金属和其他配体之间产生了许多相当小的（0-2 kJ mol〜（-1））相互作用。能量项主要是由通过两个或三个键连接的原子对产生的，即通常在分子力学水平上被忽略或按比例缩小的项，并且由r〜（-8）项具有很大的贡献。增加的分散能减小了各种广义梯度逼近（GGA）功能之间观察到的BDE的变化，而GGA和混合功能的结果之间仍然存在差距。局部MP2和CCSD（二阶微扰理论和具有单和双激发的耦合簇理论）水平的模型计算与DFT-D估计的色散相互作用（23-29 kJ mol〜（-1））在相似的范围内）。但是，DFT-D和基于波函数的结果都包括中程相关效应，由于不同的DFT方法在短程范围内基于密度的描述不同，因此它们之间的差异很大。因此，讨论哪种DFT方法给出对BDE的色散贡献的最准确估计是没有意义的。此外，为了在溶液中的结合反应过程中平衡地处理分散液，还需要考虑配体和未结合的配合物与周围环境的分散能，这将使净分散度对结合的贡献降低约20 kJ mol〜（- 1）。

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