1. Department
of Physics, H.P.T. Arts and R.Y.K. Science College, Nasik, Maharashtra 422 005, India
2. Centre
for Theoretical and Computational Molecular Science, Australian Institute
for Bioengineering and Nanotechnology, The University of Queensland, Brisbane, Qld 4072, Australia
3. Condensed
Matter Theory Group, Department of Physics and Astronomy, Uppsala University, Box
516, S-75120 Uppsala, Sweden
4. Applied
Materials Physics, Department of Materials and Engineering, Royal Institute of Technology (KTH), S-100 44 Stockholm, Sweden