Quantum renormalization group for one-dimensional fermion systems: a modified scheme

Inspired by the superblock method of White, we introduce a simple modification of the standard renormalization group (RG) technique for the study of quantum lattice systems. Our method, which takes into account the effect of boundary conditions (BC), may be regarded as a simple way to obtain first estimates of many properties of quantum lattice systems. By applying this method to the one-dimensional free and interacting fermion system, we obtain the ground state energy with a much higher accuracy than with the standard RG method. We also calculate the density-density correlation function in the free-fermion case, which shows good agreement with the exact result. (C) 1997 Elsevier Science B.V.