1. Joint BSC-IRB Research Program in Computational Biology, Barcelona Supercomputing Center, Life Science Department, Electronic and Atomic Modeling Group; Nexus II, C/Jordi Girona, 29 Barcelona 08034 Spain
2. Department of Chemistry; Yale University; New Haven Connecticut 06520-8107
3. Institució Catalana De Recerca I Estudis Avançats (ICREA); Barcelona Spain