Abstract We have performed a series of computer simulations on βPbF 2 using the molecular dynamics technique. The calculations are based on a rigid-ion model in which the particles bear the full ionic charges, the parameters of the short-range interionic potentials being chosen so as to reproduce the low temperature bulk and defect properties of the crystal. We find that the simulated system exhibits a diffuse transition from a low-conducting to a fast ion-conducting state at about 700K, in agreement with experiment. We study different methods of analyzing the defect concentration in the disordered state. We find that the value obtained for this quantity can vary by an order of magnitude depending on the method adopted. A very satisfactory analysis of both the simulated and the experimental elastic structure factors can be obtained without explicity introducing defects.