1. Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126, Pisa, Italy
2. INFN Sezione di Pisa, Pisa, Italy
3. Gaussian, Inc., 340 Quinnipiac Street, Building 40, Wallingford, Connecticut 06492, United States
4. Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, United States