Due to the principle lack of systematic improvement possibilities of density functional theory, careful assessment of the performance of density functional approximations (DFAs) on well-designed benchmark sets, for example, for reaction energies and barrier heights, is crucial. While main-group chemistry is well covered by several available sets, benchmark data for transition metal chemistry is sparse. This is especially the case for larger, chemically relevant molecules. Addressing this issue, we recently introduced the MOR41 benchmark which covers chemically relevant reactions of closed-shell complexes. In this work, we extend these efforts to single-reference open-shell systems and introduce the “reactions of open-shell single-reference transition metal complexes” (ROST61) benchmark set. ROST61 includes accurate coupled-cluster reference values for 61 reaction energies with a mean reaction energy of −42.8 kcal mol^–1. Complexes with 13–93 atoms covering 20 d-block elements are included, but due to the restriction to single-reference open-shell systems, important elements such as iron or platinum could not be taken into account, or only to a small extent. We assess the performance of 31 DFAs in combination with three London dispersion (LD) correction schemes. Further, DFT-based composite methods, MP2, and a few semiempirical quantum chemical methods are evaluated. Consistent with the results for the MOR41 closed-shell benchmark, we find that the ordering of DFAs according to Jacob’s ladder is preserved and that adding an LD correction is crucial, clearly improving almost all tested methods. The recently introduced r²SCAN-3c composite method stands out with a remarkable mean absolute deviation (MAD) of only 2.9 kcal mol^–1, which is surpassed only by hybrid DFAs with low amounts of Fock exchange (e.g., 2.3 kcal mol^–1 for TPSS0-D4/def2-QZVPP) and double-hybrid (DH) DFAs but at a significantly higher computational cost. The lowest MAD of only 1.6 kcal mol^–1 is obtained with the DH DFA PWPB95-D4 in the def2-QZVPP basis set approaching the estimated accuracy of the reference method. Overall, the ROST61 set adds important reference data to a sparsely sampled but practically relevant area of chemistry. At this point, it provides valuable orientation for the application and development of new DFAs and electronic structure methods in general.

中文翻译：

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评估化学相关开壳过渡金属反应的密度泛函理论

由于密度泛函理论缺乏系统改进可能性的原则，仔细评估密度泛函近似 (DFA) 在精心设计的基准集上的性能，例如反应能和势垒高度，是至关重要的。虽然几个可用的集合很好地涵盖了主族化学，但过渡金属化学的基准数据很少。对于较大的化学相关分子尤其如此。为了解决这个问题，我们最近推出了 MOR41 基准，它涵盖了闭壳复合物的化学相关反应。在这项工作中，我们将这些努力扩展到单参考开壳系统，并介绍了“开壳单参考过渡金属配合物的反应”（ROST61）基准集。^–1。包含 13-93 个原子覆盖 20 个 d 区元素的配合物被包括在内，但由于受单参考开壳系统的限制，铁或铂等重要元素无法考虑，或仅在很小程度上考虑。我们结合三个伦敦色散 (LD) 校正方案评估了 31 个 DFA 的性能。此外，还评估了基于 DFT 的复合方法、MP2 和一些半经验量子化学方法。与 MOR41 闭壳基准测试的结果一致，我们发现根据 Jacob 阶梯的 DFA 排序得以保留，并且添加 LD 校正至关重要，这显然改进了几乎所有测试方法。最近推出的 r ²SCAN-3c 复合方法以显着的平均绝对偏差 (MAD) 仅 2.9 kcal mol ^–1脱颖而出，只有具有少量 Fock 交换的混合 DFA（例如，TPSS0-D4/ 的2.3 kcal mol ^–1 def2-QZVPP) 和双杂交 (DH) DFA，但计算成本要高得多。使用def2-QZVPP 基组中的 DH DFA PWPB95-D4 获得的最低 MAD 仅为 1.6 kcal mol ^–1，接近参考方法的估计精度。总体而言，ROST61 集为采样稀疏但实际相关的化学领域添加了重要的参考数据。在这一点上，它为新的 DFA 和电子结构方法的应用和发展提供了有价值的方向。