[1] Department of Chemistry, USI Campus, ETH Zürich, Via Giuseppe Buffi 13, CH-6900 Lugano, Switzerland
[2] Intl. School for Advanced Studies, INFM-Democritos, Trieste, Italy
[3] Intl. Center for Theoretical Physics, P.O. Box 586, Trieste, Italy
[4] Department of Physics, Slovak University of Technology, Ilkovičova 3, 812 19 Bratislava, Slovakia