1. Department of Physics, AlbaNova University Centre, Stockholm University, Roslagstullsbacken 21, 106 91 Stockholm, Sweden
2. Department of Chemistry, Technical University of Munich, Lichtenbergstr. 4, 85748 Garching, Germany
3. Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen, Denmark
4. Department of Chemistry and Centre for Scientific Computing, University of Warwick, CV4 7AL Coventry, U.K.
5. Department of Chemistry, University College London, 20 Gordon Street, WC1H 0AJ London, U.K.