Approximation schemes for finite lattices

Abstract
Two algorithms are formulated for systematically truncating the set of basis states required in lattice Hamiltonian calculations, thus allowing larger lattice abort sizes to be treated. They are tested for the case of the (1+1)-dimensional Ising model. It is shown that smoothly convergent finite lattice sequences are obtained, which can successfully the extrapolated to the bulk limit. The authors point out the relevance of the technique for lattice calculations in higher dimensions.