Thermodynamic calculations based on hybrid-exchange density functional theory are used to predict the surface structure and stability of alpha-AIF(3) (0 1 1 2) in the presence of gaseous HF and H2O environments. The clean stoichiometric alpha-AIF(3) (0 1 1 2) is predicted to be Lewis acidic. However, under most reaction conditions this surface is unstable with respect to the adsorption of hydroxyl ions. This is consistent with experimental observations. It is predicted that the surface containing no hydroxyl ions could only be realised at high temperatures and under unrealistically dry conditions. (C) 2007 Elsevier B.V. All rights reserved.