1. ESRF, The European Synchrotron Radiation Facility, F-38000 Grenoble, France
2. Theoretical Physics Division, Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-581 83 Linköping, Sweden
3. Department of Materials and Environmental Chemistry, Stockholm University, SE-10691 Stockholm, Sweden
4. Department of Physics, Augsburg University, D-86135 Augsburg, Germany