Chapter 11 - Molecular Liquids

Abstract

The chapter discusses some of the problems that arise when the atomic systems theory is broadened to include molecular fluids. It begins by providing information on the molecular pair distribution function. Expansions of the pair distribution function are also discussed. It is pointed out that the pair distribution function for molecules of arbitrary symmetry can be expanded in terms of the Wigner rotation matrices or generalized spherical harmonics. The section focuses on linear molecules. Site–site distribution functions are then described. Correlation function expansions for simple polar fluids consider series expansions in terms of Lennard–Jones diatomics. The static dielectric constant is then detailed. This section aims at obtaining molecular expressions for the static dielectric constant. It shows, in particular, that ɛ is related to the long-wavelength behavior of each of the functions ˆhΔ(k) and .hD(k) introduced in the previous section. Integral-equation approximations for dipolar hard spheres are described. The work of Wertheim is mentioned, and the Ornstein–Zernike relation is referred to. Interaction site diagrams, interaction site models including the RISM equations, angular correlations and the RISM formalism, associating liquids, and reorientational time-correlational functions are discussed.