1. Physics Department, University of Warwick, Coventry CV4 7AL, U.K.
2. Institute of Chemistry and Center for Computing in Engineering and Sciences, University of Campinas─UNICAMP, Campinas 13084-862, Sao Paulo, Brazil
3. Scion, 49 Sala Street, Rotorua 3010, New Zealand
4. Department of Biochemistry, University of Cambridge, Hopkins Building, Downing Site, Cambridge CB2 1QW, U.K.