Magnetization of the S=2 antiferromagnetic Heisenberg chain near the critical magnetic field

Using the density-matrix renormalization-group (DMRG) technique, we carry out a large scale numerical calculation far the S=2 antiferromagnetic Heisenberg (AFH) chain. We obtain the magnetization curve of S =2 chain near the critical field. The corrections to the magnetization due to the magnon-magnon interaction are the same order for S=2 and S=1 chains. By comparing the experimental magnetization with our calculation, we find that the gap obtained experimentally is about 0.08J which is close to the accurate DMRG estimation for the S=2 AFH chain. Numerical errors in our large scale calculation are also discussed.