On the Electronic Structure of the Polar Surface of Compound Crystals

To cancel the average bulk macroscopic field compensating charge should be induced on the polar surface of compound crystals. In this paper we clarify the mechanism of the charge compensation by performing the DV-X α calculations on the clusters M 13 X 13 representing the polar surface of the rock-salt type crystals. The MgO (111) and TiC (111) surface are chosen as the example of the polar surfaces of the ionic and covalent crystals, respectively. Peculiar electronic structures of the polar surfaces leading to the charge compensation are revealed for the anion and the cation surface of these crystals. Especially metallic character of the cation surface is found, which is related to the enhanced chemical activities of these surfaces.