1. Department
of Information Technology, University of Debrecen, P.O. Box 12, H-4010 Debrecen, Hungary
2. Department
of Theoretical Physics, University of Debrecen, P.O. Box 5, H-4010 Debrecen, Hungary
3. Theoretische
Chemie, Physikalish-Chemisches Institut, Universität Heidelberg, Im Neuenheimer Feld 229, D-69120 Heidelberg, Germany