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Ab initio modeling of Bose-Einstein condensation in Pb2V3O9

We apply density functional theory band structure calculations and quantum Monte Carlo simulations to investigate the Bose-Einstein condensation in the spin-1/2 quantum magnet Pb2V3O9. In contrast to previous conjectures on the one-dimensional nature of this compound, we present a quasi-two-dimensional model of spin dimers with ferromagnetic and antiferromagnetic interdimer couplings. Our model is well justified microscopically and provides a consistent description of the experimental data on the magnetic susceptibility, high-field magnetization, and field vs. temperature phase diagram. The Bose-Einstein condensation in the quasi-two-dimensional spin system of Pb2V3O9 is largely governed by intralayer interactions, whereas weak interlayer couplings have a moderate effect on the ordering temperature. The proposed computational approach is an efficient tool to analyze and predict high-field properties of quantum magnets.