We develop powerful chemical theories and methods that enable the prediction and rational design of target molecules, nano-structures, and materials as well as new, more efficient chemical processes toward these compounds, based on quantum mechanics and computer simulations. Topics range across the entire spectrum of the molecular sciences, from physical chemistry, via organic and inorganic chemistry, to biological and supramolecular chemistry. An essential part of these efforts is theory-driven experimentation, that is, the application of our theories and models in cooperation with experimental groups.

Chemical Bonding and Reactivity Theory

One of the core interests of the group is the development of modern chemical bonding theory and models that reveal the causal relationships between electronic structure, molecular geometry as well as reactivity, and other properties (e.g., spectra, magnetic properties, etc.). Our development work is centered around quantitative molecular orbital (KS-MO) theory as contained in Kohn-Sham density functional theory (KS-DFT), a matching canonical energy decomposition analysis (EDA) method, and our Voronoi Deformation density (VDD) method for analyzing the charge density redistribution upon bond formation. Reactivity, in particular the causal physical factors behind these trends are investigated in terms of our Activation Strain Model (ASM) which works in conjunction with the PyFrag program. PyFrag is compatible with various compute engines, such as SCM's ADF, Gaussian, ORCA, and Turbomole (PyFrag bonding analyses can only be done in conjunction with ADF).

Molecular Structure, Spectra, and Archetypal Bonding Motifs

We address the fundamental questions about chemical bonding: What, for example, is the actual physical mechanism behind the stabilization that occurs when a bond is formed? Why do C–H bonds really become longer when the carbon atom goes from sp to sp2 to sp3 in an archetypal series such as acetylene, ethylene, and ethane? And we also explore the origin of trends in the length and strength of a bond A–B as the atoms A and B vary, across the periodic system. Special bonding motifs we are interested in, arise as molecules become more complex and do involve more than one bond. Examples are hypervalence or the multifaceted phenomenon of aromaticity. Besides understanding molecular structure and stability, we also have research lines on the spectral properties of molecules and how to tune them in a rational fashion.

Reactivity and Catalysis

We develop fundamental rules and frameworks to understand and predict the rate and selectivity of elementary organic and inorganic chemical reactions. This is essential to guide future experimental developments towards the design of more efficient catalytic transformations. Thus, we pinpoint the causal, physical factors which ultimately control the reactivity. Examples of our project lines are text-book organic and metalorganic reactions, homogeneous catalysis as well as organocatalysis. Insights emerging from these results can then directly be used by experimentalists to ultimately design novel and more efficient transformations.

Quantum Biological and Supramolecular Chemistry

Many central questions in both biological and supramolecular chemistry require a quantum chemical approach and this is what we do in this research program. We investigate natural and artificial supramolecular aggregates, their structure and, the reason behind the many times remarkable stabilities (cf. cooperativity), such as in DNA telomeres. Model systems of interest range from simple complexes through complex multiply hydrogen-bonded systems. In particular, we are also interested in the physical principles behind biomolecular recognition and backbone extension in enzymatic and non-enzymatic DNA replication. The project line also involves other types of intermolecular interactions, such as dihydrogen bonding, metallophilic interactions, chalcogen bonding, pnictogen bonding, and (coinage, main-group, ...) metal bonding, to name a few.

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