Physical review. B, Condensed matter
Large-Uexpansions for the Hubbard model atT=0
J. Oitmaa, Jon Henderson
Abstract
We report results for the ground-state energy of the Hubbard model in the form of perturbation expansions in t/U, i.e., expansions about the strong-coupling or ``atomic'' limit. Expansions to order (t/U${)}^{40}$ are obtained for finite cells with number of sites \ensuremath{\le}10, for the half-filled case, for both the linear chain and two-dimensional (2D) square lattice. Analysis of the series by Pad\'e approximant methods yields, in the 1D case, results consistent with the known exact results. For the largest cell, N=10, on the square lattice there is an indication of a singularity on the real t axis, which may indicate a phase transition at U/t\ensuremath{\simeq}4.