This is only the a-Al2O3 interactions of a simple transferable rigid-ion potential for binary, highly ionic oxides. The van der Waals terms involving cations and the cation–cation short-range repulsive interactions do not appear explicitly. The potential parameters are optimised for a-Al2O3, MgO and CaO. Good agreement between theory and experiment is obtained for the structural parameters and lattice energies. The new potential predicts a relaxation of the (0 0 0 1) a-Al2O3 surface which is consistent with experiment and shell model calculations.