1. Institute of Solid State Physics, Graz University of Technology, Petersgasse 16, 8010 Graz, Austria
2. Chair of Atomistic Modelling and Design of Materials, University of Leoben, Franz-Josef-Strasse 18, 8700 Leoben, Austria
3. Institut für Physik, Humboldt-Universität zu Berlin, Brook-Taylor-Strasse 6, 12489 Berlin, Germany