Ionic Liquids

Introduction

Ionic Liquids (ILs) are a subclass of molten salts which have a melting point below 100°C. ILs have been known for more than 90 years, however, recently found members of this class have shown promise in applications in electrochemistry, analytics, technology, and engineered fluids. Many ILs are liquid at room temperature, with some freezing at temperatures around -90°C. Due to their salt like structure they usually exhibit a negligible vapor pressure up to very high temperatures, making them particularly suited for "green chemistry". IL's also exhibit interesting solvation or coordination properties , suggesting that 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

• Prof. 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

• Florian Dommert, Katharina Wendler, Robert Berger, Luigi Delle Site, Christian Holm.
  Force Fields for Studying the Structure and Dynamics of Ionic Liquids: A Critical Review of Recent Developments.
  ChemPhysChem 13(7):1625–1637, 2012.
  [PDF] (691 KB) [DOI]
• Katharina Wendler, Florian Dommert, Yuan Yuan Zhao, Robert Berger, Christian Holm, Luigi Delle Site.
  Ionic liquids studied across different scales: A computational perspective.
  Faraday Discussions 154:111–132, 2012.
  [PDF] (493 KB) [DOI]
• Katharina Wendler, Stefan Zahn, Florian Dommert, Robert Berger, Christian Holm, Barbara Kirchner, Luigi Delle Site.
  Locality and Fluctuations: Trends in Imidazolium-Based Ionic Liquids and Beyond.
  Journal of Chemical Theory and Computation 7(10):3040–3044, 2011.
  [PDF] (1.0 MB) [DOI]
• Florian Dommert, Jochen Schmidt, Christian Krekeler, Yuan Yuan Zhao, Robert Berger, Luigi Delle Site, Christian Holm.
  Towards multiscale modeling of ionic liquids: From electronic structure to bulk properties.
  Journal of Molecular Liquids 152:2–8, 2010.
  [PDF] (990 KB) [DOI]
• Jochen Schmidt, Christian Krekeler, Florian Dommert, Yuanyuan Zhao, Robert Berger, Luigi Delle Site, Christian Holm.
  Ionic Charge Reduction and Atomic Partial Charges from First-Principles Calculations of 1,3-Dimethylimidazolium Chloride.
  The Journal of Physical Chemistry B 114(18):6150–6155, 2010.
  [PDF] (345 KB) [DOI]
• Christian Krekeler, Florian Dommert, Jochen Schmidt, Yuan Yuan Zhao, Christian Holm, Robert Berger, Luigi Delle Site.
  Electrostatic properties of liquid 1,3-dimethylimidazolium chloride: role of local polarization and effect of the bulk.
  Physical Chemistry Chemical Physics 12(8):1817–1821, 2010.
  [PDF] (822 KB) [DOI]
• Christian Krekeler, Jochen Schmidt, Yuan Yuan Zhao, Baofu Qiao, Robert Berger, Christian Holm, Luigi Delle Site.
  Study of 1,3-dimethylimidazolium chloride with electronic structure methods and force field approaches.
  The Journal of Chemical Physics 129(17):174503, 2008.
  [PDF] (640 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]
• 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]