1. CASPUR, SuperComputing Consortium, c/o University of Rome “La Sapienza”, P.le A. Moro 5, 00185 Rome, Italy, CNR-ISMN, Istituto per lo Studio dei Materiali Nanostrutturati, Via Salaria Km 29.3, 00016 Monterotondo S. (RM), Italy, and Department of Chemistry, Department of Electrical Engineering, and Princeton Materials Institute, Princeton University, New Jersey 08544