Realization of a large J2 quasi-2D spin-half Heisenberg system:: Li2VOSiO4 -: art. no. 186405

Exchange couplings are calculated for Li2VOSiO4 using the local-density approximation (LDA). While the sum of in-plane couplings J(1) + J(2) = 9.5 +/- 1.5 K and the interplane coupling J(perpendicular to)similar to0.2-0.3 K agree with recent experimental data, the ratio J(2)/J(1) similar to 12 exceeds the reported value by an order of magnitude. Using geometrical considerations, high temperature expansions and perturbative mean field theory, we show that the LDA-derived exchange constants lead to a remarkably accurate description of the properties of these materials including specific heat, susceptibility, Neel temperature, and NMR spectra.