Ab initio evaluation of local effective interactions in α′-NaV2O5

We will present the numerical evaluation of the hopping and magnetic exchange integrals for a nearest-neighbor t-J model of the quarter-filled alpha'-NaV2O5 compound. The effective integrals are obtained from valence-spectroscopy ab initio calculations of embedded crystal fragments (two VO5 pyramids in the different geometries corresponding to the desired parameters). We are using a large configurations interaction (CI) method, where the CI space is specifically optimized to obtain accurate energy differences. We show that the alpha'-NaV2O5 system can be seen as a two-dimensional asymmetric triangular Heisenberg lattice where the effective sites represent delocalized V-O-V rung entities supporting the magnetic electrons.