1. Departamento de Física, Universidad Autónoma Metropolitana, Iztapalapa, Apdo 55 534, Mexico DF 09340, Mexico
2. Department of Chemistry and Waterloo Institute of Nanotechnology, University of Waterloo, 200 University Avenue West, Waterloo, Ontario N2L3G1, Canada
3. Department of Mathematics and Computer Science and Institute for Complex Molecular Systems, Eindhoven University of Technology, P.O. Box 513, MetaForum, 5600 MB Eindhoven, The Netherlands
4. Department of Chemistry, Western University, 1151 Richmond Street, London, Ontario N6A5B7, Canada
5. Department of Applied Mathematics, Western University, 1151 Richmond Street, London, Ontario N6A5B7, Canada