1. neaspec GmbH, Bunsenstrasse 5, Martinsried, Munich D-821152, Germany
2. Laboratoire de Simulation Atomistique (L_Sim), SP2M,
UMR-E CEA/UJF-Grenoble 1, INAC, Grenoble F-38054, France
3. Center
for Nanoscale Systems, Harvard University, 11 Oxford Street, Cambridge, Massachusetts 02138, United States