Dynamical density functional theory for solvation dynamics in polar solvent: Heterogeneous effect of solvent orientation

Abstract

While understanding the mechanism of the solvation dynamics in polar liquid solvents is of fundamental importance, an efficient molecular theory that can capture the microscopic solvation structure and dynamics is still under development. Herein, we extend the dynamical density functional theory to describe the solvation dynamics in polar solvents by incorporating with the molecular version of classical density functional theory. The proposed theoretical model is then applied to probe the solvation dynamics of acetonitrile solvent near individual ionic solutes. Results show the heterogeneous effect of solvent orientation surrounding charged solute plays an important role in determining the characteristic of solvation dynamics. The orientation-dependent solvation free energy at solute-unfavored orientations monotonically decays, while that at solute-favored orientations reaches a minimum value rapidly by fast adsorption of solvent molecules and then increases to a plateau owning to solvent–solvent correlation. This unravels that the solvent translation and rotation are induced firstly by the solute–solvent interaction and then driven by the solvent–solvent correlation. This work not only casts molecular insights but also provides a feasible tool to explore the solvation dynamics in polar solvents.