Ab initio study of neutral and ionized microclusters of MgO

The equilibrium properties of small MgO clusters (MgO, ${\mathrm{Mg}}_2$O, ${\mathrm{MgO}}_2$, and ${\mathrm{Mg}}_2$${\mathrm{O}}_2$) are calculated to obtain their dependence on computational constraints such as the basis set and level of computation. The results have led to the suggestion that the inclusion of the correlation correction at the second-order Moller-Plesset level is necessary for the atomization energy although the configuration parameters may be obtained at the Hartree-Fock level. Based on this suggestion, the calculated properties of the neutral and single-ionized MgO monomer are in excellent agreement with the experimental data and available values from very accurate calculations. For the triatomic clusters, ${\mathrm{Mg}}_2$O is found to be more stable than ${\mathrm{MgO}}_2$, whose geometrical structure is determined by the strong O-O interaction. The optimum configuration of ${\mathrm{Mg}}_2$${\mathrm{O}}_2$ is a slightly distorted square with a ${\mathit{D}}_{2\mathit{h}}$ symmetry. Upon ionization, these clusters undergo structural modifications, but these effects are softer than in alkali halide clusters due to the delocalized character of the hole. Our results show that the evaporization of a neutral oxygen atom provides the most favorable fragmentation channel for the neutral and single-ionized stoichiometric dimers.