Cluster Variation Method, Pade` Approximants and Critical Behaviour

Abstract

In the present paper we show how non--classical, quite accurate, critical exponents can be extracted in a very simple way from the Pad\'e analysis of the results obtained by mean field like approximation schemes, and in particular by the cluster variation method. We study the critical behavior of the Ising model on several lattices (quadratic, triangular, simple cubic and face centered cubic) and two problems of surface critical behaviour. Both unbiased and biased approximants are used, and results are in very good agreement with the exact or numerical ones.