Our group is devoted to the devellopment and application of static and molecular dynamics simulations for the investigation of the mechanisms of reactions, nucleation events and self-organization processes. The addressed topics range from materials science, solid state chemistry to biophysics and general physical chemistry.
Using classical (empirical interaction models), quantum/classical and ab-initio approaches our main topics are:
Reactions in complex Systems
We explore the mechanisms of reactions in condensed phases from quantum/ classical and ab-initio molecular dynamics simulations. A special focus is dedicated to proton transfer reactions occurring during crystal aggregation and ripening.
Self-Organization of Crystals, Macromolecules and Composites
Starting from the association of single ions our simulations allow the investigation of the infancy of crystal nucleation from solution. This provides a unique level of insights into (self)-organization and its interplay with ripening reactions and interactions to growth-controlling molecules. The latter aspect allows also the investigation of hybrid materials.
Phase Transitions and Phase Separation
Our studies of phase transitions involve solid-solid, liquid-solid and liquid-vapor transformations. The main focus is dedicated to the mechanisms of phase nucleation and growth. In multinary systems also the interplay of phase transformation with segregation phenomena is explored (distillation, crystallization of eutectic systems)
Atomistic and coarse-grained models are used to explore the structure and mechanical properties of nanocrystals and bulk materials. These studies include atomic mobility, defect arrangements, dislocations, grain and phase boundaries as well as their role during deformation and fracture.
Sampling Biomolecular Systems
The immense complexity of biomolecular processes calls for advanced molecular dynamics protocols to assess the mechanims and structures involved. We devellop new simulation techniques to study biomolecule solvation, folding and docking to ligands without imposing restraints on protein flexibity or the arrangement of the solvent.
The investigation of rare barrier crossing events (reactions, nucleation processes) requires efficient simulation strategies. To tackle the time/length scale probleme we apply transition path sampling, constraint MD simulations and related approaches. Diffusion controlled processes, like crystal aggregation from dillute solutions impose different challenges to computer simulation. For this purpose, we devellop specific approaches which allow to study aggregation and growth at the atomistic level of detail.
To enable molecular mechanics or efficient QM/MM modelling at high accuracy we develop tailor-made force-fields to extend the scope of off-the-shelf models where needed. Examples are molecular mechanics models of the different states of photo-switches and molecules before/after (de)protonation reactions. Moreover, for the prospering field of modelling additives in oil and at oil-steel interfaces, our OilF force-field is continuously extended to enable the molecular simulation of anti-wear films, debris dispergion and tribology at the nm scale.
Nucleation of a molecular crystal from solution. Molecular scale insights of the infancy of the forming aggregate are used for tailoring preferential crystal motifs to enable polymorph control (Image: Zahn)
Growth of ZnO crystal impaired by an additive. Molecular simulations reveal the formation of crystal growth fronts and their interplay with growth-controlling additives (Image: Zahn)
Surfactant-surface association and monolayer organisation. Molecular scale understanding paves the way to tailoring SAM structrue and functionality (Image: Zahn)
Fracture of an apatite-collagen composite material. Coarse-graining allows accessing the mm scale.