Molecular orbital calculations on (MgO)n and (MgO)n+ clusters (n=1–13)

We report ab initio molecular orbital calculations on neutral and single-ionized stoichiometric clusters of MgO containing up to 26 atoms. Geometrical parameters of the neutral clusters are optimized at the Hartree–Fock level, whereas for the ionized clusters we have applied the vertical approximation. Correlation corrections in the clusters with 2–12 atoms are included at the equilibrium geometries by means of second order Moller–Plesset calculations. We have found that the structures based on the (MgO)3 subunit are preferred in comparison to cubelike configurations, although the energy difference decreases with the increase in cluster size. The relative stability of neutral and single-ionized clusters has been studied by means of the fragmentation path involving the loss of a neutral MgO molecule. The calculated ‘‘magic numbers’’ for the charged clusters, (MgO)n+, are in complete agreement with the abundance maxima observed in the mass spectra. Finally, we explore the size dependence of structural, energetic, and electronic properties. These properties show a large variation from the monomer to the (three-dimensional) eight atom cluster, followed by a softer approach towards the corresponding bulk limit.