The Effect of Electric Fields on the Structure of Water/Acetonitrile Mixtures

We study the effect of macroscopic electric fields on the structure of water/acetonitrile mixtures at high acetonitrile content by molecular dynamics simulations. We find that the linear response regime extends up to roughly 0.1 V nm(-1) in these mixtures, then nonlinear behavior sets in. The most pronounced nonlinear effect of an electric field is a change of relative orientations of neighboring acetonitrile molecules, from predominantly antiparallel to predominantly parallel. Nevertheless, the hydrogen bond network topology remains remarkably stable and conserves its overall properties in the whole range of considered applied fields up to 0.5 V nm(-1), which is far beyond the dielectric breakdown limit of pure water. Additionally, we report on a comparison of simulation results at zero field with experimental results and available ab-initio data using four different recently proposed acetonitrile force fields, where we find that the force field by Kowsari and Tohidifar [J. Comput. Chemistry 39, 1843, 2018] performs best. Furthermore, we demonstrate that analyzing the hydrogen bond network can be a useful tool in investigating the formation and structure of water nanodomains and their confinement by an acetonitrile matrix in water/acetonitrile mixtures.