A lattice-gas model with Coulomb interactions: Application to α-AgI

Abstract

The pair correlation function g( r) for diffusing ions has been calculated within a lattice-gas model using the tetrahedral sites of α-AgI as lattice sites and the Ag ions as particles. The Coulomb and hard core interactions between the ions have been taken into account in the hypernetted chain approximation. Using parameters appropriate for α-AgI we find that g( r) exhibits many well pronounced oscillations extending up to about 10 nearest neighbor distances. Furthermore the direct correlation function approaches the Debye—Hückel form very rapidly beyond second nearest neighbor sites. Using g we have calculated the configurational entropy and its contribution to the specific heat as functions of the temperature. Our results are compared with experiment and computer simulations.