1. Foundation for Research and TechnologyHellas, Institute of Electronic Structure and Laser, P.O. Box 1527, 711 10 Heraklion Crete, Greece; Department of Applied Mathematics, University of Leeds, Leeds LS2 9JT, U.K.; Physics Department, University of Crete, 710 03 Heraklion Crete, Greece; and Department of Chemistry, University of Athens, 157 01 Zografou Athens, Greece