Revisiting the Nature of Frequencies Shifted to Red or Blue in the <scp>LiH⋯HX</scp> Complexes (X = F, Cl, <scp>CN</scp> , and <scp>CCH</scp> ) and the Role of the Dihydrogen Bond Strength

ABSTRACT A computational study of dihydrogen‐bonded complexes formed by LiH⋯HX (X = F, Cl, CN, or CCH) at the DFT, MP2, and CCSD theoretical levels along with Pople's and Dunning's basis sets is presented. One of our main goals was to establish a direct correlation between interaction strength and the stretching frequencies of the proton donors shifted to red and blue. To this end, NBO and ChElPG atomic charge calculations were performed to quantify intermolecular charge transfers. Considering the wide range of formalisms for atomic charge calculations, the theoretical levels employed, as well as the types of intermolecular bound systems studied in this work, the application of an unsupervised statistical pattern recognition method was required. Furthermore, NCIPlot graphic visualization and QTAIM topological descriptors have characterized all dihydrogen bonds and the intermolecular covalency profile could be discussed in terms of contributions from kinetic and potential energy densities. Additionally, SAPT energy partitioning was used to evaluate the interaction strength and the trend associated with the manifestation of intermolecular covalency.