Interaction-round-a-face density-matrix renormalization-group method

We demonstrate the numerical superiority of the interaction-round-a-face (IRF) density-matrix renormalization-group (DMRG) method applied to SU(2) invariant quantum spin chains over the conventional DMRG. The ground state energy densities and the gap energies of both S = 1 and S = 2 spin chains can be calculated using the IRF-DMRG without extensive computations. We have also studied the effect of tuning boundary interaction J(end) at both ends of the chain from the IRF view point. It is clearly observed that the magnon distribution is uniform when the best J(end) is chosen. (C) 2001 Elsevier Science B.V. All rights reserved.