Understanding structure and dynamics of organic liquid mixtures by molecular simulations

The structure and dynamics of acetonitrile and its mixtures with toluene and water in the whole composition range are investigated by molecular dynamics simulations with several combinations of empirical non polarizable force fields. The acetonitrile and toluene binary system has been theoretically studied for the first time. One existing force field combination leads to unphysical phase separation in the mixture of acetonitrile with water. Densities, excess molar volumes, dielectric constants, viscosities and self-diffusion coefficients obtained by more suitable force fields are systematically compared with experimental data. For static properties, it is possible to get nearly quantitative agreement for both kinds of mixtures. The evaluation of the dielectric constant illustrates the importance of including the purely electronic component of polarization. The right trends for dynamical properties are captured. The arrangement of the closest acetonitrile molecules is antiparallel in the neat liquid, those with slightly larger separation of molecular centers orientate with respect to each other in various ways without strong preference for any of them. The addition of toluene causes structuring of acetonitrile and enhances the preference of antiparallel arrangement Water has a smaller effect on the acetonitrile radial distribution functions, but it affects the preferences for individual arrangements. (C) 2019 Elsevier B.V. All rights reserved.