1. Interdisciplinary Center for Scientific Computing, Ruprecht-Karls University, Im Neuenheimer Feld 205, D-69120 Heidelberg, Germany
2. Department of Physics, AlbaNova University Center, Stockholm University, Stockholm SE-106 91, Sweden
3. Department of Theoretical Chemistry and Biology, School of Engineering Sciences in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, SE-106 91 Stockholm, Sweden