1. Institute for Advanced Simulation, Jülich Supercomputing Centre, Forschungszentrum Jülich, Jülich D-52425, Germany
2. RWTH Aachen University, Aachen D-52056, Germany
3. Atominstitut, Vienna University of Technology, Vienna A-1020, Austria
4. Division of Applied Physics, Hokkaido University, Sapporo 060-8628, Japan
5. Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, Groningen NL-9747AG, The Netherlands