[1] Vienna Univ Technol, Inst Allgemeine Phys, A-1040 Vienna, Austria
[2] Lund Univ, Inst Phys, Dept Synchrotron Radiat Res, S-22100 Lund, Sweden
[3] Acad Sci Czech Republic, Inst Phys, CZ-18221 Prague 8, Czech Republic
[4] Ctr Computat Mat Sci, A-1060 Vienna, Austria