Tolpygo's microscopic theory was used, giving 3.066eV. The Schottky calculation for the energy of formation of a pair of defects in NaCl gave 2.047eV, whereas experiment gave 2.02eV.

Calculation of the Work of Formation of a Chlorine Vacancy in a NaCl Crystal. Z.Y.Evseev: Soviet Physics Journal, 1971, 10[4], 25-6