1. Bremen
Center for Computational Materials Science, University of Bremen, Am Fallturm 1, D-28359, Bremen, Germany
2. Institute
for Solid State Physics and Optics, Wigner Research Centre for Physics, Hungarian Academy of Sciences, Budapest, POB 49, H-1525, Hungary
3. Department
of Atomic Physics, Budapest University of Technology and Economics, Budafoki út 8, H-1111, Budapest, Hungary