Brough Harry, Cook Chris W, Griffin John M, Peach Michael J G
Department of Chemistry, Lancaster University, Lancaster, LA1 4YB, UK.
The Faraday Institution, Quad One, Didcot, OX11 0RA, UK.
Phys Chem Chem Phys. 2025 Jul 30;27(30):15906-15919. doi: 10.1039/d5cp01111f.
calculations of NMR shieldings are often used to assign spectra and help refine crystal structures in the growing field of NMR crystallography. In periodic calculations, GGA exchange-correlation functionals such as PBE and BLYP are most often used, but a "monomer correction" has recently been proposed that incorporates a "higher quality" treatment of local electronic structure into calculated shieldings. The meta-GGA functional rSCAN reportedly generates improved geometries, particularly in systems with important dispersion interactions, but has scarcely been tested for its performance in periodic shielding calculations, with or without monomer corrections. Here, the performance of rSCAN is evaluated by comparing experimental chemical shifts from 75 diverse C environments in 13 molecular solids, to chemical shifts calculated by rSCAN and PBE on geometries optimised by rSCAN, PBE and BLYP. We find rSCAN gives marginally improved geometries but produces less accurate chemical shifts than PBE. However, after a monomer correction is applied to the shieldings, corrected rSCAN consistently performs better than corrected PBE, indicating that rSCAN describes long-range contributions to shieldings more accurately than local effects. Monomer correction with a double-hybrid functional has previously been found to provide no additional benefit compared to correction with conventional hybrids. However, we show the double-hybrid mPW2PLYP predicts substantially improved chemical shifts when the monomer correction method is paired with an implicit solvation model, yielding better results than a correction with a cluster of molecules using a conventional hybrid functional. The method we find maximises agreement with experiment is a mPW2PLYP-CPCM correction to rSCAN periodic calculations on rSCAN-optimised geometries. When used on a larger set of organic crystals, with 132 C environments, this method yields unprecedented accuracy, with root-mean-square error of 0.8 ppm and mean absolute error of 0.6 ppm.
在核磁共振晶体学这一不断发展的领域中，核磁共振屏蔽计算常常用于谱图归属，并有助于优化晶体结构。在周期性计算中，最常使用的是诸如PBE和BLYP等广义梯度近似（GGA）交换关联泛函，但最近有人提出了一种“单体校正”方法，该方法将对局部电子结构的“更高质量”处理纳入到计算屏蔽中。据报道，元GGA泛函rSCAN能生成改进的几何结构，尤其是在具有重要色散相互作用的体系中，但对于其在有无单体校正的周期性屏蔽计算中的性能，几乎未进行过测试。在此，通过将13种分子固体中75个不同碳环境的实验化学位移，与在经rSCAN、PBE和BLYP优化的几何结构上由rSCAN和PBE计算得到的化学位移进行比较，来评估rSCAN的性能。我们发现rSCAN给出的几何结构略有改进，但与PBE相比，其产生的化学位移准确性较低。然而，在对屏蔽进行单体校正后，校正后的rSCAN始终比校正后的PBE表现更好，这表明rSCAN比局部效应更准确地描述了屏蔽的远程贡献。此前发现，与使用传统杂化泛函进行校正相比，使用双杂化泛函进行单体校正并没有额外的益处。然而，我们表明，当单体校正方法与隐式溶剂化模型相结合时，双杂化泛函mPW2PLYP能预测出显著改进的化学位移，其结果优于使用传统杂化泛函对分子簇进行校正的结果。我们发现与实验一致性最高的方法是对基于rSCAN优化几何结构的rSCAN周期性计算进行mPW2PLYP - CPCM校正。当应用于包含132个碳环境的更大一组有机晶体时，该方法产生了前所未有的准确性，均方根误差为0.8 ppm，平均绝对误差为0.6 ppm。
