Sets of pair potentials were derived for the γ-phases of CuCl and CuBr, using a self-consistent approach. These potentials, together with that obtained previously for γ-CuI, reproduced the sequential experimental trends in binding energies, Cu+ diffusion constants and phonon density of states. Molecular dynamics simulations using these potentials were used to explain the experimentally observed diffusion anomaly, in that the diffusion rate in CuI was similar to that in CuCl and lower than that in CuBr. It was concluded that this effect was due to a many-body interaction between dipoles induced on the large polarisable I− ions when Cu+ jumped over the energy barrier between lattice and interstitial sites.

Interpretation of the Diffusion Anomaly in the Copper Halides in Terms of the Inter-Ionic Potential. McGreevy, R.L., Zheng-Johansson, J.X.M.: Solid State Ionics, 1997, 95[3-4], 215-20