A molecular dynamics computer simulation study of room-temperature ionic liquids. I. Equilibrium solvation structure and free energetics

摘要

Solvation in 1-ethyl-3-methylmidazolium chloride and in1-ethyl-3-methylimidazolium hexafluorophosphate near equilibrium isinvestigated via molecular dynamics computer simulations with diatomic andbenzenelike molecules employed as probe solutes. It is found thatelectrostriction plays an important role in both solvation structure and freeenergetics. The angular and radial distributions of cations and anions becomemore structured and their densities near the solute become enhanced as thesolute charge separation grows. Due to the enhancement in structural rigidityinduced by electrostriction, the force constant associated with solventconfiguration fluctuations relevant to charge shift and transfer processes isalso found to increase. The effective polarity and reorganization free energiesof these ionic liquids are analyzed and compared with those of highly polaracetonitrile. Their screening behavior of electric charges is alsoinvestigated.