vspace{-0.2cm}The microscopic properties of several ZnO and ZnS surfaces of lowMiller index are investigated through first-principles calculationof the surface energy, crystal structure and electronic structure.Generally, the non-polar surfaces such as (10$ar1$0) and(11$ar2$0) are found to be more stable than the polar (0001)-Znsurface. The (11$ar2$0) surface is found to be the most stable forboth ZnO and ZnS semiconductors and the (10$ar1$0) surface isfound to have a slightly larger surface energy. These are consistentwith the abundant observations of ZnO nanostructures having(11$ar2$0) and (10$ar1$0) surfaces. The near-surface structuresand electronic structures are discussed.

Keywords: Surface Energy, ZnO, ZnS, Nanostructure