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Chemical Bond Energies of 3d Transition Metals Studied by Density Functional Theory
Journal of Chemical Theory and Computation ( IF 5.5 ) Pub Date : 2018-05-29 00:00:00 , DOI: 10.1021/acs.jctc.8b00143
Klaus A. Moltved 1 , Kasper P. Kepp 1
Affiliation  

Despite their vast importance to inorganic chemistry, materials science, and catalysis, the accuracy of modeling the formation or cleavage of metal–ligand (M–L) bonds depends greatly on the chosen functional and the type of bond in a way that is not systematically understood. In order to approach a state of high-accuracy DFT for rational prediction of chemistry and catalysis, such system-dependencies need to be resolved. We studied 30 different density functionals applied to a “balanced data set” of 60 experimental diatomic M–L bond energies; this data set has no bias toward any dq configuration, metal, bond type, or ligand as all of these occur to the same extent, and we can therefore identify accuracy bottlenecks. We show that the performance of a functional is very dependent on data set choice, and we dissect these effects into system type. In addition to the use of balanced data sets, we also argue that the precision (rather than just accuracy) of a functional is of interest, measured by standard deviations of the errors. There are distinct system dependencies both in the ligand and metal series: Hydrides are best described by a very large HF exchange percentage, possibly due to self-interaction error, whereas halides are best described by very small (0–10%) HF exchange fractions, and double-bond enforcing oxides and sulfides favor 10–25% HF exchange, as is also average for the full data set. Thus, average HF requirements hide major system-dependent requirements. For late transition metals Co–Zn, HF percentage of 0–10% is favored, whereas for the early transition metals Sc–Fe hybrid functionals with 20% HF exchange or higher are commonly favored. Accordingly, B3LYP is an excellent choice for early d-block but a poor choice for late transition metals. We conclude that DFT intrinsically underestimates the bond strengths of late vs early transition metals, correlating with increased effective nuclear charge. Thus, the revised RPBE, which reduces the overbinding tendency of PBE, is mainly an advantage for the early and mid transition metals and not very much for the late transition metals, i.e. there is a metal-dependent effect of the relative performance of RPBE vs PBE, which are widely used to study adsorption energetics on metal surfaces. Overall, the best performing functionals are PW6B95, the MN15 and MN15-L functionals, and the double hybrid B2PLYP.

中文翻译:

密度泛函理论研究3d过渡金属的化学键能

尽管它们对无机化学,材料科学和催化非常重要,但对金属-配体(ML)形成或裂解的模型进行建模的准确性在很大程度上取决于所选择的功能和键的类型,而并非系统地了解。为了接近高精度DFT的状态以合理预测化学反应和催化反应,需要解决此类系统依赖性。我们研究了应用于60个实验性双原子M–L键能的“平衡数据集”的30种不同的密度泛函。该数据集对任何d q都没有偏见构型,金属,键类型或配体都以相同的程度出现,因此我们可以确定准确性瓶颈。我们证明了功能的性能非常依赖于数据集的选择,并且将这些影响分解为系统类型。除了使用平衡数据集外,我们还认为,通过误差的标准偏差来衡量功能的精度(而不只是精度)是很重要的。在配体和金属系列中都有明显的系统依赖性:最好用很大的HF交换百分比来描述氢化物,这可能是由于自相互作用误差引起的;而最好用很小的(0-10%)HF交换分数来描述卤化物。 ,以及双键增强的氧化物和硫化物有利于10%至25%的HF交换,这也是整个数据集的平均值。因此,HF的平均需求掩盖了与系统相关的主要需求。对于较晚过渡的金属Co-Zn,HF百分比优选为0-10%,而对于较早过渡金属的Sc-Fe杂化官能团,HF交换率通常为20%或更高。因此,B3LYP是早期d嵌段的极佳选择,但对于晚期过渡金属则是较差的选择。我们得出的结论是,DFT本质上低估了后期过渡金属与早期过渡金属的结合强度,与有效核电荷增加有关。因此,降低了PBE过度结合趋势的修订版RPBE主要是对早期和中期过渡金属具有优势,而对于后期过渡金属则没有太大优势,即RPBE与PBE,广泛用于研究金属表面的吸附能。
更新日期:2018-05-29
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