Correlation functions in periodic chains

We present a simple form for the relation between correlation functions on finite periodic one-dimensional systems and the correlation function of the corresponding infinite system. This form is tested on the S=1/2 and S=1 Heisenberg models. We find good agreement with quantum Monte Carlo results for the spin correlation functions. For S=1/2 our results are consistent with the asymptotic form C(r)∼ln(r${)}^{\mathrm{\sigma }}$/r with σ=1/2.