Plaquette expansion of the Heisenberg and XY chains

Abstract

The plaquette expansions of the Lanczos matrix for the one-dimensional Heisenberg and XY models are obtained up to order 1 N5 in the number of lattice sites. The convergence of the ground state energy density calculated from the plaquette expanded Lanczos matrices in the infinite lattice limit are studied for these two models. © 1993.