LANCZOS CALCULATION FOR THE S = 1/2 ANTIFERROMAGNETIC HEISENBERG CHAIN UP TO N = 28 SPINS

Highly precise numerical calculations using a variation of the Lanczos method devised by Paige were performed for s = 1/2 antiferromagnetic Heisenberg finite chains up to sizes N = 28. Several interesting physical quantities, including the ground-state energy, the mass gap, and the spin-wave velocity, were computed and fitted for logarithmic finite-size corrections, as suggested by conformal invariance and Bethe ansatz calculations. A crossover size for a maximum of the spin-wave velocity is predicted for N approximately 50, well above the current available sizes in a typical Lanczos simulation. A list of our numerical results is given along with extrapolated values using standard algorithms.