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

TL;DR

This study uses molecular dynamics simulations to analyze the equilibrium solvation structure and free energetics of room-temperature ionic liquids, revealing the significant role of electrostriction and comparing their properties with polar solvents.

Contribution

It provides new insights into the solvation structure, free energetics, and charge screening behavior of ionic liquids through detailed molecular dynamics simulations.

Findings

Electrostriction significantly influences solvation structure.

Enhanced structural rigidity increases force constants for charge fluctuations.

Ionic liquids show distinct screening behavior compared to polar solvents.

Abstract

Solvation in 1-ethyl-3-methylmidazolium chloride and in 1-ethyl-3-methylimidazolium hexafluorophosphate near equilibrium is investigated via molecular dynamics computer simulations with diatomic and benzenelike molecules employed as probe solutes. It is found that electrostriction plays an important role in both solvation structure and free energetics. The angular and radial distributions of cations and anions become more structured and their densities near the solute become enhanced as the solute charge separation grows. Due to the enhancement in structural rigidity induced by electrostriction, the force constant associated with solvent configuration fluctuations relevant to charge shift and transfer processes is also found to increase. The effective polarity and reorganization free energies of these ionic liquids are analyzed and compared with those of highly polar acetonitrile. Their screening behavior of electric charges is also investigated.