Kröger Leif C, Müller Simon, Smirnova Irina, Leonhard Kai
Institute of Technical Thermodynamics, RWTH Aachen University, 52062 Aachen, Germany.
Institute of Thermal Separation Processes, TU Hamburg, 21073 Hamburg, Germany.
J Phys Chem A. 2020 May 21;124(20):4171-4181. doi: 10.1021/acs.jpca.0c01606. Epub 2020 May 7.
The prediction of solvation free energies is essential for a variety of applications. Solvation free energies of neutral systems can be predicted quite accurately. The accuracy of predictions for solvation free energies of ionic solutes dissolved in neutral solvents, however, has been reported to be worse by at least 1 order of magnitude. In this study, the performance of three approaches for solvation free energy prediction of several hundred ions dissolved in neutral solvents is evaluated. The applied methods are COSMO-RS, cluster continuum model (CCM) together with COSMO-RS, and COSMO-RS-ES. It is emphasized that the reference data for model evaluation are subject to large uncertainties stemming from the impossibility to measure the so-called elusive absolute free energies of solvation of a single ion. Consequently, such uncertainty must be considered during the evaluation of prediction methods. Therefore, a straightforward approach to account for the underlying uncertainty is applied here. Hereby, it is revealed that the true performance of the method is better than what is often reported. The average absolute deviation (AAD) of COSMO-RS is calculated to be 2.3 kcal mol, while applying the CCM and COSMO-RS-ES each results in AADs of 2.0 kcal mol. This accuracy allows for qualitative assessment of solvation free energy-dependent quantities, such as reaction rate constants.
溶剂化自由能的预测对于各种应用至关重要。中性体系的溶剂化自由能能够被相当准确地预测。然而，据报道，溶解在中性溶剂中的离子溶质的溶剂化自由能预测准确性至少要差一个数量级。在本研究中，对三种用于预测溶解在中性溶剂中的数百种离子的溶剂化自由能的方法的性能进行了评估。所应用的方法有COSMO-RS、与COSMO-RS结合的簇连续介质模型（CCM）以及COSMO-RS-ES。需要强调的是，用于模型评估的参考数据存在很大的不确定性，这源于无法测量单个离子所谓难以捉摸的绝对溶剂化自由能。因此，在评估预测方法时必须考虑这种不确定性。所以，这里采用了一种直接的方法来考虑潜在的不确定性。由此发现，该方法的实际性能比通常报道的要好。计算得出COSMO-RS的平均绝对偏差（AAD）为2.3 kcal/mol，而应用CCM和COSMO-RS-ES时，AAD均为2.0 kcal/mol。这种准确性使得能够对依赖于溶剂化自由能的量，如反应速率常数进行定性评估。
