1. University of Bremen Institute for Physical and Theoretical Chemistry Leobener Straße NW2 D-28359 Bremen Germany
2. Current address: University of Bremen, UFT Leobener Str. 6 D-28359 Bremen Germany
3. University of Bremen Bremen Center for Computational Materials Science Am Fallturm 1 D-28359 Bremen Germany
4. University of Bremen MAPEX Center for Materials and Processes Bibliothekstraße 1 D-28359 Bremen Germany