MATERIALS OF JUBILEE 250th NATIONAL WORKSHOP ON STUDYING THE STRUCTURES OF LIQUIDS AND SOLUTIONS The Ornstein-Zernike Equation, Critical Phenomena, and the Equation of State for Liquids and Gases

It is shown that the OrnsteinZernike (OZ) equa tion has two solutions: the standard one, which depends explicitly on the interaction potential, and a second universal one, resulting from the infinity point of the partition function. It is stressed that there are two pressure components: the standard one and a univer� sal one that is valid over the whole of the phase plane. It is concluded that the universal solution parameters depend in general on definite integrals of functions dependent on the interaction potential. In the vicinity of the critical point, however, the dependence on the interaction potential vanishes; i.e., the solution becomes fully universal. It is shown that in this range of the phase diagram, all results of the theory of critical phenom� ena (scaling theory) follow from the OZ equation.