Theory of the radial distribution functions in α-AgI

The three partial radial distribution functions g_Ag-Ag(r), g_Ag-I(r) and g_I-I(r) in α-AgI are calculated on the basis of the fact that I-ions form a bcc lattice and Ag-ions are randomly distributed over the 12(d) sites. The short-range order between the Ag-ions is described in terms of the microcrystalline model which has been recently divised by the present author on the occasion of the study on the superionic transition in CuI. The calculated results are in good agreement with those of the computer simulation of Vashishta and Rahman. We have an evidence that the Ag-ions are correlated in order to decrease the Coulomb interaction between them (not core-core repulsion) and the microcrystalline model is suitable to represent the correlated region. We discuss the relation between the microcrystalline model and the caterpillar mechanism.