The renormalization group method for quantum mechanical systems. I. The s = 1/2 XY model on the square lattice

Abstract

The renormalization group method is reformulated for application to quantum mechanical many-particle systems situated on regular lattices in two or three-dimensional configuration space. The method is applied to the spin 1/2 XY model on the square lattice. The free energy curve is in excellent agreement with that obtained from high temperature series expansion. No critical temperature is found.