1. Institute of Theoretical Chemistry, Faculty of Chemistry, University of Vienna, Währinger Str. 17, A-1090 Wien, Austria
2. Departamento de Química, Universidad Autónoma de Madrid, c/Francisco Tomás y Valiente 7, 28049 Cantoblanco, Madrid, Spain
3. Dipartimento di Chimica e Chimica Industriale, University of Pisa, Via G. Moruzzi 13, 56124 Pisa, Italy