1. Taras Shevchenko National University of Kyiv, Kyiv 01601, Ukraine
2. Bogolyubov Institute for Theoretical Physics of the National Academy of Sciences of Ukraine, Kyiv 03143, Ukraine
3. Institut fur Theoretische Festkorperphysik, Karlsruher Institutfur Technologie, D-76I3I, Germany
4. Helmholtz-Zentrum Dresden-Rossendorf e.V., Institute of Ion Beam Physics and Materials Research, Dresden 0I328, Germany
5. Kyiv Academic University, Kyiv 03I42, Ukraine