The Phase Diagram of the Hubbard Model: A Variational Wavefunction Approach.

We explore the phase diagram of the Hubbard model by generalizing the Gutzwiller variational wavefunction to take into account nearest neighbor spin correlations. At half filling we obtain an antiferromagnetic state, in agreement with previous results. Slightly away from half filling, the Gutzwiller approximation yields a lower energy than that found for spin polarons. Thus, we find no evidence to support the existence of small spin bags.