Potential of Mean Force for An Ionic Liquid Ion-Pair In n-Pentanol by Molecular Dynamic Simulation with Window Sampling

Molecular dynamic (MD) simulation is performed to investigate the dissociation of a single ion-pair of the ionic liquid 1-hexyl-3-methylimidazolium tetrafluoroborate ([Hmim][BF₄]) in n-pentanol. The simulation results show that the ions tend to be strongly associated in agreement with experiment. The ion-pair potential of mean force (PMF) is obtained from window sampling (Figure) and dissociation constant is calculated and compared with experimental measurement. In addition, the favorable association structures of the [Hmim][BF₄] ion-pair, based on PMF, are analyzed from the MD results. For comparison, simulations were performed at both room temperature and 400K. Translational motions of these ions were also investigated. Simulation of single ion BF₄ or Hmim in 1-pentanol gives diffusion coefficient D₊ and D_-, which can be combined to evaluate average molecular diffusion coefficient D_+-, which is relevant to analysis of our experiments.