Homopolar bond formation in ZnV$_2$O$_4$ close to a metal-insulator   transition
  Electronic structure calculations for spinel vanadate ZnV$_2$O$_4$ show that partial electronic delocalization in this system leads to structural instabilities. These are a consequence of the proximity to the itinerant-electron boundary, not being related to orbital ordering. We discuss how this mechanism naturally couples charge and lattice degrees of freedom in magnetic insulators close to such a crossover. For the case of ZnV$_2$O$_4$, this leads to the formation of V-V dimers along the [011] and [101] directions that readily accounts for the intriguing magnetic structure of ZnV$_2$O$_4$. 
V. Pardo, S. Blanco-Canosa, F. Rivadulla, D.I. Khomskii, D. Baldomir,   Hua Wu, J. Rivas