Haldane gap for the S=2 antiferromagnetic Heisenberg chain revisited

Using the density matrix renormalization group (DMRG) technique, we carry o ut a large scale numerical calculation for the S = 2 antiferromagnetic Heis enberg chain. Performing systematic scaling analysis for both the chain len gth L and the number of optimal states kept in the iterations m, the Haldan e gap Delta (2) is estimated accurately as (0.0876 +/- 0.0013)J. Our system atic analysis for the S = 2 chains not only clarifies the controversies ari sing from various DMRG calculations and Monte Carlo simulations, but also s heds light on how to obtain reliable results from the DMRG calculations for other similar complicated systems. [S0163-1829(99)03237-3].