Stability of MgO(111) Polar Surface:  Effect of the Environment

The stability, structural, and electronic properties of various structural models of the polar MgO(111) surface have been investigated using density functional theory in combination with a thermodynamic formalism. The most stable phase is the O-terminated octopolar structure under the oxygen-rich regime, which is almost degenerate with Mg-terminated octopolar in energy. For oxygen-poor conditions, the Mg-terminated 1 × 1 structure is the favorite phase and Mg-terminated α and O-terminated×surfaces also become more stable than the octopolar structure. Our calculations indicate that charge compensation induced by reconstruction will cancel the polarity and oxygen chemical potential plays a very important role in the stability of the polar surface. We also find that a large surface relaxation and change of the electronic structure occur in the considered surfaces, which provide additional stabilization of these polar surfaces.