1. Institute for Condensed Matter Physics, National Academy of Sciences of Ukraine, Svientsitskii Street 1, 79011 Lviv, Ukraine
2. Department for Theoretical Physics, I. Franko National University of Lviv, Lviv, Ukraine
3. Institute of Physical Chemistry, Polish Academy of Sciences, 01-224 Warsaw, Poland
4. Max-Planck-Institut für Intelligente Systeme, Heisenbergstraße 3, D-70569 Stuttgart, Germany
5. IV. Institut für Theoretische Physik, Universität Stuttgart, Pfaffenwaldring 57, D-70569 Stuttgart, Germany