SURFACE ATOMIC AND ELECTRONIC-STRUCTURE OF ZNO POLYMORPHS

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 (approximately 0.54 angstrom) 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 (approximately 0.01 angstrom), we observe no surface relaxation of the rocksalt structure.