Second-neighbours contribution to the repulsive energy of crystalline alkaline-earth oxides

The Born-Mayer model in the alkaline-earth oxides is reconsidered, using new compressibility data. All four oxides cannot share a unique hardness parameter ϱ. An exact solution is found by assuming that ϱ (MgO) = ϱ (CaO) and ϱ (SrO) = ϱ (BaO); another solution is proposed, which involves three distinct ϱ values in the family of salts. Results are tested by calculating the electron affinity of O 2- from each salt.