1. a Department of Physics , Ovidius University of Constanţa , Constanţa , Romania
2. b Department of Theoretical Chemistry and Biology , Royal Institute of Technology , Stockholm , Sweden
3. c Department of Chemistry , B. Khmelnitsky National University , Cherkassy , Ukraine
4. d Department of Theoretical Chemistry , Institute of Physical Chemistry , Bucharest , Romania
5. e Department of Inorganic Chemistry , University of Bucharest , Bucharest , Romania