(2×2) reconstructions of the {111} polar surfaces of GaAs

Ab initio total-energy calculations were used to examine (2×2) reconstruction models for the (111) and (1¯1¯1¯) surfaces of GaAs. For the (111) surface the lowest-energy Ga-vacancy geometry is determined; several mechanisms for Ga-vacancy formation are examined and other reconstructions are discussed. For the (1¯1¯1¯) surface it is shown that the As-vacancy model is unlikely and other geometries are considered.