A NEW METHOD TO PREDICT CRITICAL-TEMPERATURE OF THE ISING-MODEL BY EXTRAPOLATING VARIATIONAL CUMULANT EXPANSION TO INFINITE-ORDER

The critical temperatures of the Ising model in square and simple cubi c lattices are derived with the variational-cumulast expansion aproach to the seventh order. An extrapolating method is proposed to predict the critical temperature of infinite series according to the finite or der expansion, at which a weighted fitting method is used, For the 2-d imensional Ising model, the critical temperature obtained by this meth od is in a deviation of 0.04% compared with the exact value, and the e stimated results are robust for different order prediction. The critic al temperature for the 3D Ising model is predicted as 4.490.