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Research

Research Areas of of the Kirchner Group

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Selected publications:

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Structure and Lifetimes in Ionic Liquids (187):
Ionic liquids derive their properties from a subtle interplay between weak (e.g., hydrogen bonds) and strong (e.g., ionic forces) interactions. However, questions such as how long does a hydrogen bond live, or how long do two ions aggregate are notoriously difficult to answer, since a myriad of other mechanisms (e.g., diffusion) couples to the elementary dynamic processes of interest. Here, we apply advanced methods to isolate the target dynamics and to answer the fundamental questions raised above.
Keywords: Ionic Liquids, structure, lifetime

Material Synthesis in Ionic Liquids (179):
The near room temperature material synthesis in ionic liquids (ILs) currently is a subject of immense academic interest. To illuminate molecular-level details, molecular simulations of a single Te4Br2 molecule, dissolved in [C2C1Im][Cl] as well as in the same IL mixed with AlCl3, were performed. In both systems, a significant structuring was observed. However, only in the AlCl3-containing liquid, the reaction of the chain-like Te4Br2 molecule to a square-like Te4Br+ takes place, the first step towards the Te2Br material formation.
Keywords: Ionic Liquids, structure, materials, solvent effects

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toc_185.png Lithium-Doped Ionic Liquids (185):
We investigate Lithium-doped bis­(trifluoro­methane­sulfonyl)­imide-based ionic liquids, via molecular dynamics, as potential electrolytes for rechargeable lithium batteries. Lithium addition systematically weakens the hydrogen-bonded network and charge ordering in the liquids. Formation of lithium-anion aggregates appears to be significant in the investigated electrolytes. We observe an inhomogeneous structuring mechanism, consistent with a 'universal' type of ion solvation.
Keywords: Ionic liquids (structure, materials, energy devices), Solvent effects

Quantum Cluster Equilibrium (184):
The quantum cluster equilibrium (QCE) model applies statistical mechanics to quantum chemically optimized clusters in order to describe fluid thermodynamics. In this work we apply the QCE method to four binary mixtures of standard solvents, including the hardly miscible water/benzene system. We demonstrate that our low-cost approach is able to correctly predict the mixing behavior of all systems, providing new means of understanding the importance of distinct structure motifs and their influence on the systems thermodynamics.
Keywords: cluster approach, fluid phase, solvent mixtures, statistical thermodynamics

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toc_183.png Searching for cheap and sustainable solutions (183):
Deep eutectic solvents (DES) display the essential advantage of having a good environmental bio-compatibility and low toxicity. They are a cheap and sustainable alternative to ionic liquids in various processes such as SO2 absorption. From ab initio molecular dynamics simulations we found that SO2 is incorporated within the hydrophobic part of the DES, while the hydrogen bonding interaction within the DES is disrupted, which leads to the fluidization of the DES.
Keywords: deep eutectic solvent, ab initio molecular dynamics simulations, SO2 absorption
CO2 absorption (174):
The reduction of the amount of the green house gas CO2 in earth's atmosphere is necessary to prevent the global climate change. One way to achieve this aim is to capture the CO2 with ionic liquids based for example on building blocks of amino acids and many other building principles, which are easily obtainable from natural sources. Therefore, we apply the newest theoretical methods to understand the details of the way the CO2 reacts with the amino acids. Our insights will be a helpful support for the tuning of the capturing process.
Keywords: ab initio calculations, CO2 absorption, amino acids, ionic liquids, reaction mechanisms
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toc_167.png Energy Devices (167):
Properties of the ionic liquid-surface interface are of crucial interest for electrochemical devices, but their investigation via molecular dynamics requires large simulation cells. Thus, classical interaction potentials have been derived from accurate calculations, allowing for extended simulations. Application of the derived model reveals new insights in the interface structure, which has some possible implications for the use of the ionic liquids as electrolytes, for example in solar cells.
Keywords: ionic liquids, energy devices, polarisable force fields
Spectroscopy (156):
With the development and application of a new analysis tools within TRAVIS with respect to vibrational spectroscopy, an excellent tool for comparison between experiment and ab initio molecular dynamics simulations is provided, which also helps in assigning peaks of the experimental spectrum. By utilizing the Voronoi tessellation of the electron density, infrared and Raman spectra of similar and even superior quality could be achieved, especially in systems with significant charge transfer.
Keywords: vibrational spectroscopy, ab initio molecular dynamics simulations, Voronoi tessellation, infrared spectra, Raman spectra
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toc_140.png Floating Orbitals Molecular Dynamics (140):
A variation of Born-Oppenheimer molecular dynamics is the so-called floating orbital molecular dynamics. Rather than using atom-centered basis functions – as practiced in conventional electronic structure methods – the basis functions' centers are optimized in each timestep. Besides the fact that floating orbitals can replace polarization functions, further advantages of FOs can be identified: certain problems such as non-nuclear attractors or hydrated electrons may be better described. Furthermore, Pulay forces can be avoided if floating basis functions are applied.
Keywords: Gaussian Type Orbitals, Basis Sets, Ab Initio Methods, Molecular
Dynamics, Electronic Structure

 

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