1. Department of Chemistry Chemical Theory Center, and Minnesota Supercomputing Institute University of Minnesota 207 Pleasant St. SE Minneapolis MN 55455-0431 USA
2. Laboratoire de Chimie Physique, CNRS UMR8000, Bat. 349 Université de Paris-Sud 91405 Orsay Cédex France
3. Institute of Chemistry The Hebrew University of Jerusalem Givant-Ram Campus Jerusalem 9190407 Israel
4. Department of Chemistry Iowa State University and Ames Laboratory Ames IA 50014 USA