Intermolecular interactions in an equimolar methanol-water mixture: Neutron scattering, DFT, NBO, AIM, and MD investigations

Abstract

A detailed analysis of equimolar methanol–water (MeW) liquid structure at 298 K and atmospheric pressure is performed using neutron scattering, Density Functional Theory (DFT) calculation and Molecular Dynamics (MD) simulations. New neutron scattering data at large scattering wave vectors were explored to determine the structure factor SMq , the molecular form factor F1q and the intermolecular pair correlation function gLr . To describe the local order of the mixture, a large variety of H-bonded clusters has been optimized using DFT calculation with the 6–311++ G(d, p) basis. Experimental data were interpreted in terms of two cyclic trimers involving respectively 2Me-1W and 2W-1Me molecules. A detailed study of the H-bond interactions in the most probable clusters in the mixture was performed using Natural Bond orbital (NBO) and Atomsin Molecules (AIM) analyses. To have more structural information about the mixture at medium and large distances as well as the dynamic of molecules in solution, MD simulations were performed using three force fields. Our results show that several H-bonds between water molecules and between methanol ones are broken in favor of the formation of water-methanol H-bonded clusters. The self-diffusion coefficients of monomers decrease when going from the pure to the mixed states.