Gutzwiller magnetic phase diagram of the undoped t-t′-U Hubbard model

We calculate the magnetic phase diagram of the half-filled t-t'-U Hubbard model as a function of t' and U, within the Gutzwiller approximation plus random-phase approximation. As U increases, the system first crosses over to one of a wide variety of incommensurate phases, whose origin is clarified in terms of double nesting. We evaluate the stability regime of the incommensurate phases by allowing for symmetry breaking with regard to the formation of spin spirals, and find a crossover to commensurate phases as U increases and a full gap opens. The results are compared with a variety of other recent calculations, and in general good agreement is found. For parameters appropriate to the cuprates, double occupancy should be only mildly suppressed in the absence of magnetic order, inconsistent with a strong-coupling scenario.