On the origin of the root 7 x root 7 superstructure and the anomalous magnetic and transport properties of the layered compound Sr6V9S22O2

We examined why the IT-VS2 layer of the layered compound Sr6V9S22O2 has the root7 x root7 superstructure in terms of electronic band structure calcula tions and metal-metal bonding across the shared edges of adjacent VS6 octah edra. On the basis of this analysis we explored how the anomalous magnetic and transport properties of Sr6V9S22O2 can be explained. Our work shows tha t the root7 x root7 superstructure is not caused by a charge density wave i nstability associated with Fermi surface nesting but by the metal-metal bon ding through the shared edges of adjacent VS6 octahedra. The weak and stron g electron localizations observed for Sr6V9S22O2 were discussed in terms of three-center two-electron and two-center two-electron V-V bonds in the IT- VS2 layers.