INFLUENCE OF PAIR CORRELATIONS ON PHASE TRANSITION IN AN ISING LATTICE

We propose a method to incorporate pair correlations of an Ising lattice system in molecular field theory to higher orders. The theory is applied to ferromagnetism, where a system of equations is obtained for the response function (here the susceptibility). We obtain important corrections on the Weiss model and the spherical model. This is illustrated by an explicit calculation of the critical temperature and the spurious phase, appearing for T>Tc, near the critical point in the case of a simple cubic lattice. © 1969 The American Physical Society.