OPERATOR RENORMALIZATION-GROUP AND SPIN SYSTEMS

The results of a new hybrid method for calculating ground-state energies for lattice Hamiltonians are presented. This method combines the t expansion with the real-space renormalization-group approach, with the hope of extracting infinite-volume physics at t --> infinity from calculations of only a few powers of t. We calculate the ground-state energy for the (1 + 1)-dimensional anisotropic Heisenberg model and the (1 + 1)-dimensional Ising model. Using a blocking that treats the sites and links symmetrically, we were able to determine the exact critical point of the Ising system. In both of these systems we see that the operator renormalization-group method substantially improves upon the results of either the t expansion or real-space renormalization-group methods used separately.