Simulation of small positively charged MgO clusters and study of their electronic densities

With the help of ab initio methods the clusters $[(\mathrm{MgO})_{13}\mathrm{Mg}]^{Q+}$ are simulated for Q = 0, 1, 2. Then, vacancy clusters $[(\mathrm{MgO})_{12}\mathrm{Mg}_{2}]^{Q+}$ obtained by removing one oxygen atom are computed for Q running from 0 to 4. These clusters exhibit a slight sphericity and generally shorter interatomic distances than in the crystal. The electronic densities variations are studied in function of Q. In particular, it is observed that the electronic density in the oxygen vacancy goes to a maximum when Q = 2. The ionisation potentials vary from approximately 4 to 14 eV when Q varies from 0 to 3, with a more rapid increase from Q = 1 to Q = 2. The stability study of vacancy clusters show that they experience a phase transition when their charge becomes equal to 2, in accordance with the features mentioned above