Structure and properties of low-dimensional materials
Low-dimensional materials can be defined as compounds of unusual structure that extend to less than three dimensions. Examples are two-dimensional surfaces, thin films and interfaces, one-dimensional nanotubes and nanowires as well as zero-dimensional nanoparticles, large molecules and clusters. The interest in such materials range from material science and nanotechnology through to astrophysics.
The key prerequisite for understanding the chemical and physical properties of existing low-dimensional materials and for designing new ones is a detailed knowledge of their atomic structure. However, such materials frequently present complex structures to solve. This is because on one hand the structural information is difficult to access experimentally and on the other hand the accuracy of theoretical tools that can be applied to extended systems is often limited. The results of our research show that often only a close collaboration between theory and experiment makes possible the successful atomic structure determination of low-dimensional materials. In particular, the application of global optimization methods at an ab initio level of theory has proved very useful in an automatic structure resolution of such systems.
Nanoparticles and clusters
Nanoparticles are of great scientific interest as they often display properties intermediate between bulk materials and atomic or molecular structures. In addition, one of the fundamental issues of materials science is how the structure, properties and reactivity of a material change with its increasing aggregation state – from small molecules and clusters through nanostructures to the three-dimensional bulk phase.
In this project the study of nanostructured metal oxides aggregates are carried out using atomistic modeling tools. The use of global optimization methods is essential for the determination of atomic structures of such nanoparticles, since their structures often differ fundamentally from their bulk counterparts. The most important recent achievements within this project include structure determinations of
- neutral MgO clusters (Phys. Chem. Chem. Phys. 2012, 14, 2849-2856; Angew. Chem. Int. Ed. 2011, 50, 1716–1719)
- partially reduced gas-phase cerium oxide clusters (Phys. Chem. Chem. Phys. 2011, 13, 19393-19400)
- aluminum oxide clusters (ChemPhysChem 2009, 10, 2410-2413.; J. Am. Chem. Soc. 2008, 130, 15143-15149.)
Thin films, surfaces and interfaces
Two-dimensional thin films, surface layers and interfaces play a crucial role in many modern technologies, e.g., electronic semiconductor devices, optical coatings, solar cells and batteries. The knowledge of the atomic structure of such materials is of great importance for their successful applications and for improving their functionality. Our results within this project demonstrate that a successful structure resolution of two-dimensional materials can often only be achieved by a combination of theory and experiment.
The most recent achievements within this project include atomic structure determinations of
- metal-supported vitreous thin silica film (Angew. Chem. Int. Ed. 2012, 51, 404–407)
- ordered water monolayers on MgO(001) (J. Phys. Chem. C 2011, 115, 6764–6774)
- crystalline silica sheet on Ru(0001) (Phys. Rev. Lett. 2010, 105, 146104-1-146104-4)
Nanostructured coordination compounds
This project involves scientific collaboration with the group of Prof. Dr. M. Scheer at the Institute of Inorganic Chemistry, University of Regensburg. Here, the focus is on exploration of possible synthetic routes and structural characterization of coordination compounds with unusual main group elements ligands. Particularly important is the ligand-induced stabilization of otherwise unstable species. Our contribution is the computational support and theoretical interpretation of experimental data. The development of efficient computational methods is of particular importance since the chemical compounds investigated within this project usually contain several hundred atoms. Examples of the most important recent achievements within this project include synthesis and characterization of
- an organometallic nanosized capsule (Angew. Chem. Int. Ed. 2011, 50, 1435–1438)
- extended polyphosphorus frameworks (Angew. Chem. Int. Ed. 2010, 49, 6860-6864)
- spherical 90-vertex fullerene-like nanoballs (Chem. Eur. J 2010, 16, 2092–2107)
Hybrid QM/MM studies of oxide materials
Hybrid quantum mechanics/molecular mechanics (QM/MM) and quantum mechanics/quantum mechanics (QM/QM) methods allow for simulations of much larger systems than accessible by QM methods alone. This project focuses on applications of the hybrid methods for ab initio modeling of the structure and reactivity of oxide materials. The recent problems tackled within this project include