A SELF-CONSISTENT ORNSTEIN-ZERNIKE APPROXIMATION FOR THE SITE-DILUTEDISING-MODEL

We propose a theory for the site-diluted Ising model which is an exten sion to disordered systems of the self-consistent Ornstein-Zernike app roximation of Hoye and Stell. By using the replica method in the conte xt of liquid-state theory, we treat the concentration of impurities as an ordinary thermodynamic variable. This approach is not limited to t he weak-disorder regime or to the vicinity of the percolation point. A preliminary analysis using series expansion shows that it can predict accurately the dependence of the critical temperature on dilution and can reproduce the nonuniversal behavior of the effective exponents. T he theory also gives a reasonable estimate of the percolation threshol d.