Univ.-Prof. DDr. Klaus Liedl
Theoretical Chemistry
Electron structure methods such as Coupled Cluster (CC) allow the precise quantum mechanical modelling of molecular electronic properties and form the basis for more advanced methods such as vibrational configuration interaction (VCI), which find an accurate solution of the nuclear Schrödinger equation and thus allow a precise description of the anharmonic, coupled vibrations of small atmospherically relevant molecules. On the other side of the size spectrum, molecular modelling and molecular dynamics (MM/MD) techniques allow the study of proteins and the interactions they undergo with ligands in their binding pocket.
Matrix isolation IR spectrum of CO2 in neon. Theoretical methods allow accurate prediction of the relative intensity and wavenumber at which the band occurs.
If a photon with suitable energy hits a molecule, various electronic, rotational and vibrational transitions can be stimulated in this molecule by absorption of the photon. This property of molecules is the reason for the ubiquitous greenhouse effect. Most of the radiation from the sun passes through our atmosphere, but the back radiation from earth, which is in the IR range, interacts with the molecules in our atmosphere. In current climate models, our atmosphere is greatly simplified. They only consider monomers that do not interact with each other. However, due to the very high local water content in the atmosphere, cluster formation is inevitable. These clusters show a different IR activity than the respective monomers, which leads to a change in the absorbed back radiation. Part of our research is aimed at modelling such effects using theoretical methods and subsequently confirming them experimentally.
The identification of molecules outside our planet is a very complex endeavour. In order to prevent background noise from the Earth's own atmosphere, telescopes such as the James Webb Space Telescope have to be brought up to 1.5 million kilometres into space to the Lagrange point L2. However, this alone is not enough, the flood of data received is still very noisy and the target signal often only accounts for a tiny fraction of the overall intensity. Correct identification is only possible with highly accurate reference data. Part of our work therefore focusses on the provision of highly accurate IR reference data, which is usually a combination of highly accurate calculated spectra and experimental vibration spectra. The aim is to achieve a holistic assignment and a coherent notation of the vibrational spectrum of the target molecule by understanding the theoretical data.
Almost all biochemical reactions take place in aqueous solution. In order to understand properties such as stability and interactions in the binding pocket of a protein, it is essential to find an accurate description of the thermodynamics of the solvation process. This knowledge enables the identification of binding sites and the prediction of binding affinities of a protein and can drastically accelerate the first steps in drug development Therefore, part of our research focusses on the active development of Grid Inhomogenous Solvation Theory (GIST), a computational method that calculates the statistical solvent properties of grid points of a grid stretched around the molecule of interest.