1. Department of Materials; Royal School of Mines and the Thomas Young Centre, Imperial College London; London SW7 2AZ United Kingdom
2. Department of Physics; Sri Guru Gobind Singh College, Sector 26; Chandigarh 160019 India
3. Department of Chemistry and Paderborn Center for Parallel Computing; University of Paderborn, Warburger Str. 100; Paderborn D-33098 Germany