NUMERICAL RENORMALIZATION-GROUP STUDY OF THE CORRELATION-FUNCTIONS OF THE ANTIFERROMAGNETIC SPIN-1/2 HEISENBERG CHAIN

We use the density-matrix renormalization-group technique developed by White to calculate the spin correlation functions [S-n+l(z) Sn-z]=(-1)(l) omega(l,N) for isotropic Heisenberg rings up to N=70 sites. The correlation functions for large l and N are found to obey the scaling relation omega(l,N)=omega(l,infinity)f(XY)(alpha)(l/N) proposed by Kaplan ef at, which is used to determine omega(l,infinity). The asymptotic correlation function omega(l,infinity) and the magnetic structure factor S(q=pi) show logarithmic corrections consistent with omega(l,infinity)similar to a root lncl/l, where c is related to the cut-off dependent coupling constant g(eff)(l(0))=1/ln(cl(0)), as predicted by field theoretical treatments.