Atomic and molecular clusters.
Clusters are the `missing link' between molecular and condensed matter. In the context of nanoscience, they are of great relevance as building bricks for novel materials with tunable properties. We analyze various groups of metal and semiconductor clusters with respect to their geometric, energetic, electronic and magnetic features. Particular emphasis is placed on hybrid systems, such as metal atom impurities in silicon cages. These investigations, being performed in collaboration with experimentalists, are directed at the design of silicate based nanomaterials with well-defined mechanic, optical and thermal properties. Further, we analyze clusters supported by periodic substrates. While experimental data on clusters attached to substrates are plentiful, relatively few computational investigations have been devoted to this theme which may be attributed to the difficulty of the describing the interaction between a finite system in contact with a periodic substrate. Extending our previous work on silicon clusters deposited on graphite, we are in the process of investigating a wide range of cluster-surface systems in terms of geometric and electronic structure, conductivity and dynamic features. The goal of these studies is a comprehensive theory of the cluster-surface interaction. They are based on various ab initio and Density Functional methods as well as First Principles Molecular Dynamics techniques.

Electron density distribution for a Si4 cluster deposited on graphite (from: J.Wu, F. Hagelberg, Density Functional Studies of Small Silicon Clusters Adsorbed on (0001) and (001) Diamond, Phys. Rev.B 76, 155409 (2007)).

An additional recent project related to cluster science is directed at the understanding of fullerenes enclosing metallic species. The interest in these species is largely based on their potential for application as novel Magnetic Resonance Imaging (MRI) contrast agents which promise to be more useful and safer than the chelated compounds currently utilized in medical MRI examinations. As suggested by experimental assessment, these units can also be used to enhance the efficiency of X-ray analysis as well as radiographic diagnosis and therapy. The computational work on these species in my group is intended to aid the design of these novel pharmaceutical nanodevices by clarifying the architecture of complex systems combined of fullerene cages and encapsulated metal clusters.

Formation of Self-Assembled Monolayers.
Self-assembled monolayers (SAMs) are molecular films that form spontaneously on solid surfaces. These systems have been the subject of intense research in recent years, both experimental and computational, due to their importance in tribology, chemical and biological sensing, optics and nanotechnology. Among the many varieties of SAMs, alkanethiol molecules on the Au(111) surface have been given special attention because of the relative simplicity of their structure, their highly stable and ordered SAM patterns, and the ease of preparing the Au(111) surface. Despite the apparent simplicity of this system, its observation in various experiments has led to controversial results. Using a variety of computational methods, we try to understand the preferred adsorption geometries, the dissociation and dimerization features of these systems from first principles.

Quantum Dynamics.
Another focus of my present research is theoretical molecular physics, more specifically Quantum dynamics of molecular interactions. My work in this field deals predominantly with nonadiabatic molecular processes, an increasingly relevant and rapidly expanding discipline of molecular quantum dynamics which involves transitions between electronic states. These occur typically in cases of reactive scattering between molecules, photoexcitation, collisions with electrons or strong vibronic and rotational coupling between electronic and nuclear degrees of freedom in the gas phase or in condensed media. The high interest in understanding nonadiabatic molecular effects can be partially attributed to the advent of Femtosecond Laser Spectroscopy and the rapid development of this discipline during the last two decades. The ability of experimentalists to resolve ultrafast processes associated with dramatic changes of the electronic system of a molecule calls for an adequate response from the side of theorists.