Structures of pure and Ca-segregated MgO (001) surfaces

The structures of pure and Ca-segregated MgO (001) surfaces have been studi ed using first-principles density-functional theory. The relaxation and rum pling for the pure surface are found to be 0.48% and 1.62%, respectively. C a segregation significantly modifies the surface structure. The surface-seg regated Ca atoms protrude outwards owing to the size mismatch between Ca an d Mg. Consequently, their nearest neighbor oxygen atoms are pulled up. The value of the protrusion of Ca atoms is strongly dependent on the Ca coverag e of the surface. (C) 1999 Published by Elsevier Science B.V. All rights re served.