Classical density functional theory reveals coexisting short-range structural decay and long-range force decay in ionic liquids

We look into the electrostatic screening in ionic liquids through the calculations of structural profiles and surface forces inside the slit system with varying width. The strong ion-ion correlation is modeled with ion pair association using reaction-based classical density functional theory. The equilibrium densities and ion pair fraction are solved iteratively. For pure ionic liquids, the oscillation of charge density is damped over relatively short range while surface force decays exponentially in the long range. Pair fraction approaches the bulk value asymptotically with growing slit width. Different components of surface force are identified according to various types of interactions.