Structural and electronic properties of the (100) surface and bulk of alkaline-earth metal oxides

Electronic and structural properties of the (100) surfaces and bulk of MgO, CaO, SrO, and BaO have been studied using the projector augmented wave (PAW) method within the local density approximation and generalized gradient approximation. Relaxed (100) MgO shows the positive rumpling of 2.2% whereas (100) CaO, (100) SrO, and (100) BaO exhibit increasingly negative rumpling and surface contraction. (100) CaO is a border case between the two trends and the sign of the rumpling of this surface can be changed at distortion. We find that the surface structures obtained as a result of relaxation are largely determined by an increasing interaction between the cation semicore states and oxygen p states observed in the oxide series.