1. Department of Mathematics and Statistics, University of Otago, Dunedin 9054, New Zealand
2. School of Science and Technology, University of New England, Armidale 2351, NSW, Australia
3. Sackler Sciences Center, Department of Chemistry, Clark University, Worcester, Massachusetts 01610, United States
4. Lennard-Jones Laboratories, Birchall Centre, Keele University, Keele, Staffordshire ST5 5BG, U.K.
5. Department of Chemistry, University of Otago, Dunedin 9054, New Zealand