Parametrized canonical transformation for the Hubbard-model at arbitrary interaction strength


The $t-J$ and Heisenberg models are truncated expansions of a canonically transformed Hubbard model coinciding with it at $U\to \infty$. We show that a modified canonical transformation applied to the Hubbard model leads to alternative models of the same form, but whose convergence properties with respect to the expansion are more favourable, resulting in a good description of the half-filled ground state even at $0<U\leq1$. We investigate the transformed Hamiltonian and observables for metallic and insulating variational wave-functions.Comment: to appear in Physical Review B (Brief reports) added author names and addresses (which were missing in the first version) revised version: 1. There was an error in Fig. 2, now fixed. 2. Minor text revision

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