Entwicklung von quantenmechanischen Simulationsmethoden zum computergestützten Materialdesign
Computationally aided development of novel materials requires an efficient and reasonably accurate simulation methods capable of describing both molecular as well as extended systems on an equal footing. Therefore, the methodological part of this thesis is devoted to an efficient implementation of density functional theory within the TURBOMOLE program package, which enables simulations of both molecules and extended systems under periodic boundary conditions on an equal footing. Specifically, my contribution has been the improvement of efficiency and usability of the program by addressing its bottlenecks, extension to open shell systems and implementation of analytical energy gradients. In particular, an efficient, octree-based continuous fast multiple method has been implemented in order to significantly speed up Coulomb energy and gradient calculation. With the improved efficiency and usability this implementation has been applied to atomic level structural characterization of ZnO and CdO nanoclusters. As the result, not only new structures are discovered, but it is also possible to demonstrate that their extraordinary long-lived excited states are due to electronhole pair localization combined with structural rigidity of the nanoclusters. Finally, mixed ZnO-TiO2 nanoclusters as well as ZnO clusters adsorbed on the anatase (101) surface have been investigated. Striking structural similarities between structures of mixed ZnO-TiO2 and pure TiO2 clusters are found. In case of ZnO nanoclusters adsorbed on the anatase surface a significant reduction of the band gap of the system is shown. This suggest the way to tune electronic properties of TiO2-based materials, in particular for solar cell applications, by deposition of ZnO nanoclusters on anatase-like nanostructures.
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