Fine tuning the intermolecular interactions of water clusters using dispersion-corrected density functional theory

Dispersion-inclusive density functional theory (DFT) methods have unequivocally demonstrated improved performances with respect to standard DFT approximations for modeling large and extended molecular systems at quantum mechanical level. Yet, in some cases, disagreements with highly accurate reference calculations, such as CCSD(T) and quantum Monte Carlo (MC) calculations, still remain. Besides, the application of general-purpose corrections, such as the popular Grimme’s semi-classical models (DFT-D), to different Kohn-Sham exchangecorrelation functionals sometimes leads to variable and inconsistent results, which recommend a careful prior evaluation. In a recent study, we proposed a simple optimization protocol for enhancing the accuracy of DFT-D methods by following an alternative and system-specific approach. Here, adopting the same computational strategy, we show how accurate MC intermolecular interactions of a large set of water clusters of variable size (i.e., 300 (H2O)n structures, n = 9, 15, 27, taken from J. Chem. Phys. 141, 014104 (2014)) can be reproduced remarkably well by dispersion-corrected DFT models (i.e., B3LYP-D4, PBE-D4, revPBE(0)-D4) upon reoptimization, reaching a mean absolute error per monomer of ~0.1 kcal/mol. Hence, the obtained results support the use of this procedure for fine-tuning tailored DFT-D models for the accurate description of targeted molecular systems.