Na2V3O7, a frustrated nanotubular system with spin-1/2 diamond rings
  Following the recent discussion on the puzzling nature of the interactions in the nanotubular system Na2V3O7, we present a detailed ab-initio microscopic analysis of its electronic and magnetic properties. By means of a non-trivial downfolding study we propose an effective model in terms of tubes of nine-site rings with the geometry of a spin-diamond necklace with frustrated inter-ring interactions. We show that this model provides a quantitative account of the observed magnetic behavior. 
T. Saha-Dasgupta, Roser Valenti, F. Capraro, C. Gros