Density-matrix renormalization-group study of S=1/2 Heisenberg spin chains: Friedel oscillations and marginal system-size effects

We report a density-matrix renormalization-group (DMRG) study of S=1/2 antiferromagnetic Heisenberg spin chains. We show the Friedel oscillations in open spin chains within bosonization theory. The bosonization predictions are in excellent agreement with the DMRG calculation. The chain length dependence of the ground state and several low-energy excited state energies are compared with conformal field theory results. Based upon the DMRG calculations for various quantities, the interplay between the system size and the number sf optimal states kept in the DMRG is carefully discussed.