Mulliken Center for Theoretical Chemistry, Universität Bonn, Beringstr. 4, 53115 Bonn, Germany.
Phys Chem Chem Phys. 2021 Jan 6;23(1):287-299. doi: 10.1039/d0cp04696e.
Conformational energies are an important chemical property for which a performance assessment of theoretical methods is mandatory. Existing benchmark sets are often limited to biochemical or main group element containing molecules, while organometallic systems are generally less studied. A key problem herein is to routinely generate conformers for these molecules due to their complexity and manifold of possible coordination patterns. In this study we used our recently published CREST protocol [Pracht et al., Phys. Chem. Chem. Phys., 2020, 22, 7169-7192] to generate conformer ensembles for a variety of 40 challenging transition metal containing molecules, which were then used to form a comprehensive conformational energy benchmark set termed TMCONF40. Several low-cost semiempirical, density functional theory (DFT) and force-field methods were compared to high level DLPNO-CCSD(T1) and double-hybrid DFT reference values. Close attention was paid to the energetic ordering of the conformers in the statistical evaluation. With respect to the double-hybrid references, both tested low-cost composite DFT methods produce high Pearson correlation coefficients of rp,mean,B97-3c//B97-3c = 0.922 and rp,mean,PBEh-3c//B97-3c = 0.890, with mean absolute deviations close to or below 1 kcal mol-1. This good performance also holds for a comparison to DLPNO-CCSD(T1) reference energies for a smaller subset termed TMCONF5. Based on DFT geometries, the GFNn-xTB methods yield reasonable Pearson correlation coefficients of rp,mean,GFN1-xTB//B97-3c = 0.617 (MADmean = 2.15 kcal mol-1) and rp,mean,GFN2-xTB//B97-3c = 0.567 (MADmean = 2.68 kcal mol-1), outperforming the widely used PMx methods on the TMCONF40 test set. Employing the low-cost composite DFT method B97-3c on GFN2-xTB geometries yields an slightly improved correlation of rp,mean,B97-3c//GFN2-xTB = 0.632. Furthermore, for 68% of the investigated complexes at least one low-energy conformer was found that is more stable than the respective crystal structure conformation, which signals the importance of conformational studies. General recommendations for the application of the CREST protocol and DFT methods for transition metal conformational energies are given.
构象能是一种重要的化学性质，需要对理论方法进行性能评估。现有的基准集通常仅限于生化或主族元素含分子，而有机金属体系通常研究较少。这里的一个关键问题是由于其复杂性和可能的配位模式的多样性，通常需要为这些分子常规生成构象。在这项研究中，我们使用了我们最近发表的 CREST 协议[Pracht 等人，Phys. Chem. Chem. Phys.，2020，22，7169-7192]为各种 40 种具有挑战性的过渡金属含分子生成构象系综，然后将其用于形成一个全面的构象能基准集，称为 TMCONF40。比较了几种低成本的半经验、密度泛函理论（DFT）和力场方法与高水准的 DLPNO-CCSD(T1)和双杂交 DFT 参考值。在统计评估中，特别关注构象的能量排序。相对于双杂交参考，两种测试的低成本复合 DFT 方法都产生了高 Pearson 相关系数 rp,mean,B97-3c//B97-3c = 0.922 和 rp,mean,PBEh-3c//B97-3c = 0.890，平均绝对偏差接近或低于 1 kcal mol-1。对于一个称为 TMCONF5 的较小子集的 DLPNO-CCSD(T1)参考能量的比较，也具有良好的性能。基于 DFT 几何形状，GFNn-xTB 方法产生了合理的 Pearson 相关系数 rp,mean,GFN1-xTB//B97-3c = 0.617（MADmean = 2.15 kcal mol-1）和 rp,mean,GFN2-xTB//B97-3c = 0.567（MADmean = 2.68 kcal mol-1），在 TMCONF40 测试集上优于广泛使用的 PMx 方法。在 GFN2-xTB 几何形状上使用低成本复合 DFT 方法 B97-3c 可以得到略微改善的相关系数 rp,mean,B97-3c//GFN2-xTB = 0.632。此外，对于 68%的研究复合物，至少有一个低能量构象比各自的晶体结构构象更稳定，这表明构象研究的重要性。为过渡金属构象能的 CREST 协议和 DFT 方法的应用提供了一般建议。
