1. “Vinča” Institute of Nuclear Sciences, Laboratory of Theoretical Physics and Condensed Matter Physics, 11001, Belgrade, P. O. Box 522, Yugoslavia, Fax: (internat.) +381‐11‐8065829
2. Department of Chemistry, University of Belgrade, Studentski trg 16, 11000 Belgrade, Yugoslavia, Fax: (internat.) +381‐11‐638‐785