1. IBM T.J. Watson Research Laboratory−Yorktown, Route 134 & PO Box 218, Yorktown Heights, New York 10598-0218, Laboratoire de Chimie Théorique, Université Pierre et Marie Curie, Tour 22-23, 1er étage, Case 137, 4 place Jussieu, 75252 Paris, France, Department of Chemistry, New York University, New York, New York, 10003-6688