Theory of polar fluids

Abstract

The theory of fluids of polar polarizable molecules is extended using the previous formalism based on renormalization. Exact formal expressions are derived for the pressure, entropy and internal energy at three levels of renormalization. Thermodynamic perturbation theory is developed, and numerical estimates are made for polar polarizable hard spheres. The effect of the polarizability α on the Helmholtz free energy A predicted by the two renormalized versions is much larger than the prediction of the unrenormalized version, which is in essential agreement with the unrenormalized perturbation theory of McDonald. The renormalized theories predict a strong dependence on the anisotropy of α, while no such dependence is predicted by the unrenormalized theories. The numerical values and the dependence on the anisotropy of α are in good agreement with the results of the more complicated perturbation treatment of Patey and Valleau, which requires detailed knowledge of a rigid polar reference system obtainable only by computer simulation. The results indicate that the use of renormalized perturbation theory is required, even for small values of α.