Finite-lattice extrapolations for a Haldane-gap antiferromagnet

Abstract
We present results of exact diagonalization of the isotropic antiferromagnetic S=1 Heisenberg chain by the Lanczos method, for finite rings of up to N=22 sites. The Haldane gap G(N) and the ground-state energy per site e(N) converge, with increasing N, faster than a power law. By VBS and Shanks transformations, the extrapolated values are G(∞)=0.41049(2) and e(∞)=-1.401485(2). The spin-spin correlation function is well fit by exp(-r/ξ)/ √r with ξ=6.2.
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