CLUSTER VARIATION METHOD, PADE APPROXIMANTS, AND CRITICAL-BEHAVIOR

In the present paper we show how nonclassical, quite accurate, critica l exponents can be extracted in a very simple way from the Pade analys is of the results obtained by mean-field-like approximation schemes, a nd in particular by the cluster variation method. We study the critica l behavior of the Ising model on several lattices (quadratic, triangul ar, simple cubic and face centered cubic) and two problems of surface critical behavior. Both unbiased and biased approximants are used, and results are in very good agreement with the exact or numerical ones.