1. I. Physikalisches Institut (IA); RWTH Aachen; 52056 Aachen Germany
2. Chemical Sciences Division; National Institute of Standards and Technology; Gaithersburg Maryland 20899 United States
3. Institut für theoretische Festkörperphysik; RWTH Aachen; 52056 Aachen Germany
4. JARA-Fundamentals of Future Information Technology; RWTH Aachen; 52056 Aachen Germany