Shell and breathing shell model calculations for defect formation energies and volumes in magnesium oxide

The authors have calculated defect energies for MgO using both a simple central-force shell model and the central-force breathing shell model proposed by Sangster (1973). Such an extension is required to account for the large Cauchy violation C 44 >>C 12 found for this material. A critical comparison has been made of various techniques used in such calculations and studied the effect of including the many-body force in an effective two-body interaction. The results are rather insensitive to the model and method of calculation as long as the model reproduces the dielectric behaviour of MgO correctly. The calculated Schottky energies are so large (7.4-7.9 eV) that no intrinsic diffusion could be observed.