title: Ionic liquids studied across different scales: a computational perspective.
abstract: For theoreticians, ionic liquids represent a major challenge. This is due to the fact that intermolecular interactions are particularly strong because of ionic liquids' ionicity. This, in turn, causes a subtle interplay between different scales which is encoded in the measured macro- and mesoscopic properties and also in the molecular electrostatic characteristics. Therefore, force fields have to describe the microscopic processes correctly in order to reproduce macroscopic properties accurately over a large range of state variables. Herein, imidazolium-based ionic liquids were studied at different scales, going from the detailed quantum electronic scale to the classical atomistic scale. It is indicated how the information gained at each level could be used for the other scales. In particular, the issue of deriving suitable partial charges for use in classical force fields is addressed. The Blöchl method was employed to generate partial charges reproducing the multipole distribution accurately for bulk systems. This led naturally to absolute ionic charges of less than /l e/, i.e., charge scaling. So, the monopole structure of the herein introduced force field mimics the quantum chemical behaviour observed in the liquid phase. This led to a substantial improvement in the description of dynamical properties of immediate experimental interest, such as electric conductivity. For further insight, the electric dipole moment of the ions was taken as physical indicator of their electronic structure. The electric dipole moment was found to fluctuate strongly and to depend on polarisation. Hence, our scale-combined study offers a gateway to rational design of models, based on the relevant underlying physics rather than on mere numerical parameterisation, and thereby to (possibly) more direct physical interpretation of experimental results.
authors.affiliation: Max Planck Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz, Germany.
authors.forename: Katharina
authors.initials: K
authors.lastname: Wendler
authors.forename: Florian
authors.initials: F
authors.lastname: Dommert
authors.forename: Yuan Yuan
authors.initials: YY
authors.lastname: Zhao
authors.forename: Robert
authors.initials: R
authors.lastname: Berger
authors.forename: Christian
authors.initials: C
authors.lastname: Holm
authors.forename: Luigi
authors.initials: L
authors.lastname: Delle Site
mesh_terms: D052578:Ionic Liquids / Q000737:chemistry*; D056004:Molecular Dynamics Simulation; D011789:Quantum Theory
chemical_list: D052578:Ionic Liquids