Exploring the Effect of External Electric Field on the Hydrogen Bonding of Methanol Dimer and Fluorinated Methanol Dimer: A Quantum Chemical Investigation

It is well established that external electric fields (EEFs) influence the H-bond network of liquid methanol and methanol clusters and induce proton transfer reactions. In this paper, a detailed ab initio study of the structural changes and energetics in the methanol dimer and its fluorine substituted dimers under the influence of EEFs of varying strengths is performed by employing density functional theory (DFT) and coupled-cluster with singles and doubles (CCSD) theory. The geometries are optimized using a wide variety of DFT functionals, spanning from the GGA (revPBE) functional to hybrid GGA (B3LYP, revPBE0) to meta-GGA (M06-2X) and double-hybrid functionals (B2PLYP). The structures and energy values from these calculations are benchmarked against the CCSD results. Furthermore, QTAIM calculation is performed on the methanol dimer to get insights into the nature of the H-bonding interactions. The H-bonds are observed to strengthen in the presence of EEFs, as demonstrated by other studies. It is shown that all DFT functionals overestimate the H-bond distance by 18-20%. This shows a strong dependence of the methanol dimer under the electric field at the DFT level. Furthermore, QTAIM predicts an increase in H-bonding energy under the influence of the electric field. The fluorine-substituted methanol dimers exhibit the same picture of structure and energetics. Overall, this study provides a deeper understanding of the H-bonding interaction under the electric field of methanol and its substituted systems.