1. Faculty of Physics, University of Vienna 1 , Kolingasse 14-16, A-1090 Vienna, Austria
2. VASP Software GmbH 2 , Sensengasse 8, A-1090 Vienna, Austria
3. Faculty of Physics and Vienna Doctoral School in Physics, University of Vienna 3 , Boltzmanngasse 5, A-1090 Vienna, Austria
4. Institute for Theoretical Physics, TU Wien 4 , Wiedner Hauptstraße 8-10/136, 1040 Vienna, Austria