Internal energy, diffusion coefficients, ion-ion correlation functions, anion density and characteristics of ionic motion in barium gadolinium fluoride (Ba1-xGdxF2+3 00.1, both 4b and 48i positions in the lattice were relatively favorable for interstitial F- ions. At low dopant concentrations, anion migration in the simulated system takes place mainly by the interstitialcy mechanism with noncollinear hops. The computer experiment confirmed that trigonal Gd3+-F-(interstitial) "dipole complexes" are preferable in comparison with tetragonal ones. Existence of the tendency to clustering of gadolinium ions in the simulated system was also confirmed using elements of Monte Carlo technique. (C) 2003 Elsevier Science B.V. All rights reserved.