title: Are there stable ion-pairs in room-temperature ionic liquids? Molecular dynamics simulations of 1-n-butyl-3-methylimidazolium hexafluorophosphate.
abstract: Molecular dynamics simulations with an all-atom model were carried out to study the ionic liquid 1-n-butyl-3-methylimidazolium hexafluorophosphate, [bmim][PF(6)]. Analysis was carried out to characterize a number of structural and dynamic properties. It is found that the hydrogen bonds are weaker than expected, as indicated by their short lifetimes, which is due to the fast rotational motion of anions. Transport properties such as ion diffusion coefficients and ionic conductivity were also measured on the basis of long trajectories, and good agreement was obtained with experimental results. The phenomenon that electrical conductivity of ionic liquids deviates from the Nernst-Einstein relation was well reproduced in our work. On the basis of our analysis, we suggest that this deviation results from the correlated motion of cations and anions over time scales up to nanoseconds. In contrast, we find no evidence for long-lived ion-pairs migrating together.
authors.affiliation: Eduard-Zintl-Institut für Anorganische und Physikalische Chemie, Technische Universität Darmstadt, Petersenstrasse 20, D-64287 Darmstadt, Germany. w.zhao@theo.chemie.tu-darmstadt.de
authors.forename: Wei
authors.initials: W
authors.lastname: Zhao
authors.forename: Frédéric
authors.initials: F
authors.lastname: Leroy
authors.forename: Berit
authors.initials: B
authors.lastname: Heggen
authors.forename: Stefan
authors.initials: S
authors.lastname: Zahn
authors.forename: Barbara
authors.initials: B
authors.lastname: Kirchner
authors.forename: Sundaram
authors.initials: S
authors.lastname: Balasubramanian
authors.forename: Florian
authors.initials: F
authors.lastname: Müller-Plathe