Structure of room temperature ionic liquids

The structure of room temperature ionic liquids is studied using molecular dynamics simulations and integral equation theory. Three ionic liquids 1-alkyl-3-methylimidazolium hexfluorophosphate, [C n MIM] [PF6], for n = 1, 4, and 8, are studied using a united atom model of the ions. The primary interest is a study of the pair correlation functions and a test of the reference interaction site model theory. There is liquid-like ordering in the liquid that arises from electrostatic attractions and steric packing considerations. The theory is not in quantitative agreement with the simulation results and underestimates the degree of liquid-like order. A pre-peak in the static structure factor is seen in both simulations and theory, suggesting that this is a geometric effect arising from a packing of the alkyl chains.