Static transverse dielectric function of model molecular fluids

• Published in: The Journal of chemical physics 1993-06, Vol.98 (11), p.8910-8918
• Main Authors: RAINERI, F. O, FRIEDMAN, H. L
• Format: Article
• Language: English
• Subjects: Collective effects; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Electron states; Exact sciences and technology; Exchange, correlation, dielectric and magnetic functions, plasmons; Physics
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.464450

It is customary in the physicochemical literature to define the static transverse dielectric function of a polar fluid according to the relation εT(k) = 1 + 4πβST(k), where β=(kBT)−1 and ST(k) is a measure of the static fluctuations of the Fourier components of the transverse part of the electric polarization field in the fluid. In this work we evaluate εT(k) for models of two classes. (1) In a DS model each molecule is a hard sphere with a point dipole at its center. It is the simplest representative of models in which the long range intermolecular interactions are generated by a set of point multipoles located at a single point in the molecule. In this case ST(k) is SM,T(k), the static correlation function of the transverse part of the dipole polarization density M̂(k). (2) In a ζDS model fluid, comprising nonideal dipolar hard spheres, the long range interactions are accounted for by two opposite partial charges on either side of the sphere’s center and separated by a distance ℓ. The ζDS model is the simplest interaction site model (ISM) of a polar fluid. For an ISM the relevant structure factor ST(k) is SPμ ,T(k), the static correlation of the transverse part of the full electric polarization density vector P̂μ(k). Here we compare εT(k) for DS and ζDS models with the help of the mean spherical approximation for the required structure functions. The ζDS–DS difference in εT(k) at large k is found to parallel the behavior of the static longitudinal dielectric function εL(k). However, εT(k), unlike εL(k), is a damped oscillatory function of k with no poles on the real k axis.