Exact Universal Amplitude Ratios for Two-Dimensional Ising Models and a   Quantum Spin Chain
  We have derived analytic expressions for the amplitudes of correction terms in the critical free energy and inverse correlation length expansions for square, honeycomb, and plane-triangular lattices in strip geometry. We have found that ratio of amplitudes for all of these lattices is universal. We have also obtained similar expansions for the ground state energy and the first energy gap of a critical quantum spin chain and find that the amplitude ratios have the same values. 
N.Sh. Izmailian and Chin-Kun Hu