1. Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand, Department of Mathematics, Faculty of Science, Khon Kean University, Khon Kaen 40002, Thailand, and Department of Molecular Dynamics/Computer Simulation, Faculty of Physics and Geoscience, Institute for Theoretical Physics (ITP), University of Leipzig, Augustplatz 0-11, 04109 Leipzig, Germany