1. Istituto per i Processi Chimico-Fisici (IPCF-CNR), Area della Ricerca, via G. Moruzzi 1, I-56124 Pisa, Italy, Laboratory of Theoretical Chemistry, Royal Institute of Technology, SE-106 91 Stockholm, Sweden, and Hefei National Laboratory for Physical Sciences at the Microscale, USTC, Hefei, Anhui 230026, People's Republic of China