[1] Univ Roma Tor Vergata, Dipartimento Fis, Via Ric Sci 1, I-00133 Rome, Italy
[2] Univ Studi Roma Tor Vegata, Dipartimento Fis & Ctr, NAST, I-00133 Rome, Italy
[3] CNR IPCF Sezione Messina, Messina, Italy
[4] NQ Inst Mat, Lab Computat Sci & Modelling, Ecole Polytechn Federale Lausanne, Lausanne, Switzerland
[5] Queen Mary Univ London, Sch Biol & Chem Sci, London E14NS, England
[6] Ruhr Univ, Lehrstuhl Theoret Chem, D-44780 Bochum, Germany
[7] Rutherford Appleton Lab, ISIS Facil, Didcot OX11 OQX, Oxon, England
[8] UCL, Dept Phys & Astron, London WC1E 6BT, England
[9] Aberystwyth Univ, Ctr Adv Funct Mat & Devices, Inst Math & Phys, Aberystwyth 5Y23 3BZ, Dyfed, Wales
[10] Univ Cambridge, Dept Mat Sci & Met, Cambridge BB2 3QZ, England
[11] Univ Durham, Dept Phys, Durham DILL 3LE, England
[12] Nottingham Trent Univ, Sch Sci & Technol, Nottingham NG11 8N5, England
[13] Univ Houston, Dept Phys, Houston, TX 77204 USA