1. Department of Chemistry, Duke University, Durham, North Carolina 27708
2. School of Natural Sciences, University of California, Merced, 5200 North Lake Road, Merced, California 95343
3. UPMC Univ Paris 06, UMR 7616, Laboratoire de Chimie Théorique, case courrier 137, 4 place Jussieu, F-75005, Paris, France
4. CNRS, UMR 7616, Laboratoire de Chimie Théorique, case courrier 137, 4 place Jussieu, F-75005, Paris, France