DIELECTRIC-CONSTANT OF DIPOLAR HARD-SPHERES

An interaction-graph theory for the dielectric constant e of a fluid of hard spheres, each of diameter d and with central point dipole moment p., is developed. In particular, we consider the Debye function (e— 1)/(e + 2) expanded as Lan(p*)yn, where y = 4irpfi2/9kT, p is the number density, p* = pd a1(p») = 1, a2(p*) = 0 and a3(p*)= - $ +0-0313p* +…. The dominant term — # was derived earlier by Jepsen by a different method. The coefficients of the terms in p*2 y* and p*x yi are calculated (and are small). It is proved that the coefficients of terms proportional to yn (without further powers of/>*) are the same in Patey's recent LHNC theory as in Wertheim's mean spherical approximation: and the implication of this for Patey's theory is discussed. Independent support for the validity of Patey's predictions at high densities is cited. It is argued that e for water can never be accounted for by treating the molecules as (polarizable) dipolar hard spheres: charge separation must play a dominant role in determining. © 1979 Taylor & Francis Group, LLC.