Ionic Liquids

Introduction

Ionic Liquids (ILs) are basically a subclass of molten salts, which have a melting point below 100°C. ILs are known already for more than 90 years, however, only recently newly found members of this class showed promising applications in electrochemistry, analytics, technology, and engineering fluids. Many ILs are already liquid at room temperature, some even freeze only at temperatures around -90°C. Due to their salt like structure they usually exhibit a negligible vapor pressure up to very high temperatures which makes them particularly suited for "green chemistry". Since they can also exhibit interesting solvation or coordination properties, one could potentially use them as "designer solvents".

Our Project

We follow a multiscale approach capable of predicting the bulk and the molecular structure of ionic liquids and some of their micro- and macroscopic properties. Our idea is to treat selected ionic liquids within a sequential multiscale framework spanning from highly accurate ab initio-methods (post Hartree-Fock), to medium scale density functional theory methods (plain waves and Car-Parrinello methods) up to classical atomistic molecular dynamics simulations and possibly beyond to coarse grained models. We started from the Angstrom length scale with the individual ions and ion pairs and now successively develop effective potentials and classical force fields representing accurately the small systems to be able to simulate progressively larger structures until length and time scales are reached which resolve most accurately the bulk properties and also the solvation structure with solutes. This procedure is applied iteratively from the quantum system to the classical one and vice versa until an accurate "modeling" description is achieved, satisfying in a reasonable way the main scales involved and providing the required framework for the prediction and interpretation of experimental results.

Our group currently focusses on classical dynamics simulations of ILs and the improvement of the underlying force fields with the help of ab-initio calculations.

Current Coworkers

• PD Dr. Christian Holm, Project supervisor
• Florian Dommert, PhD Student

Former Coworkers

• Dr. Baofu Qiao, Former Post-Doctoral Fellow
• Dr. Jochen Schmidt, Post-Doctoral Fellow

Collaborations

We are members of the priority program "Ionic Liquids" of the DFG (DFG-SPP1191).

Our multiscale project is a shared project of our group and

• Dr. Robert Berger, Frankfurt Institute for Advanced Studies (post Hartree-Fock)
• Dr. Luigi Delle Site, MPI for Polymer Research, Mainz (Density-Functional Theory calculations).

Publications

• Baofu Qiao, Christian Krekeler, Robert Berger, Luigi Delle Site, Christian Holm.
  Effect of Anions on Static Orientational Correlations, Hydrogen Bonds, and Dynamics in Ionic Liquids: A Simulational Study.
  The Journal of Physical Chemistry B 112(6):1743–1751, 2008.
  [PDF] (361 KB) [DOI]
• Florian Dommert, Jochen Schmidt, Baofu Qiao, Yuanyuan Zhao, Christian Krekeler, Luigi Delle Site, Robert Berger, Christian Holm.
  A comparative study of two classical force fields on statics and dynamics of [EMIM][BF₄] investigated via molecular dynamics simulations.
  The Journal of Chemical Physics 129(22):224501, 2008.
  [PDF] (642 KB) [DOI]