1. Thomas Young Centre, University College London, London WC1H 0AH, United Kingdom
2. London Centre for Nanotechnology, Gordon St., London WC1H 0AH, United Kingdom
3. Department of Physics and Astronomy, University College London, London WC1E 6BT, United Kingdom
4. Department of Earth Sciences, University College London, London WC1E 6BT, United Kingdom
5. Interdisciplinary Center for Scientific Computing, University of Heidelberg, Im Neuenheimer Feld 205A, 69120 Heidelberg, Germany
6. Dipartimento di Fisica Ettore Pancini, Università di Napoli Federico II, Monte S. Angelo, I-80126 Napoli, Italy