The formation energies of cation and anion vacancies at 0K at a (100) surface were calculated using the method of Mort and Littleton. The value for a cation-anion vacancy pair was 2.12eV; slightly greater than the corresponding bulk value of 1.90eV.

Formation Energies of Vacancies at a (100) Sodium Chloride Surface. J.M.Blakely, C.Y.Li: Journal of Physics and Chemistry of Solids, 1965, 26[12], 1863-7