The surface atomic and electronic structures of the zinc-blende-, wurtzite-, and rocksalt-structure polymorphs of ZnO are investigated within a unified tight-binding (TB) model. For the fourfold-coordinated wurtzite and zinc-blende structures, large relaxations (∼0.54 Å) of the surface atoms are observed as a consequence of their ability to undergo approximately bond-length-conserving motions. For the sixfold-coordinated rocksalt structure, these motions are prohibited by the close-packed surface topology. Thus, only small movements of the cation and anion are expected in the direction normal to the surface. Within the resolution of this TB model (∼0.01 Å), we observe no surface relaxation of the rocksalt structure.

• Received 17 September 1991

DOI:https://doi.org/10.1103/PhysRevB.45.3557