The six lowestσ-bonded potential surfaces for the reaction K+NaCl=KCl+Na have been calculated on a semi-empirical model with a single valence electron in the field of the three closed shell ions. A simple method is proposed by which the energetic effects of valence-core orthogonalization, which are of crucial importance in the calculations, may be included in the potentials of the ions. Test calculations on the ions Na2+and K2+are in good agreement with experiment.