Structural stability and its electronic origin of the GaAs(111)A-2 × 2 surface

The stability of the vacancy-buckling (VB) structure of the GaAs(111)A-2 × 2 surface is investigated with the use of the first-principles total energy pseudopotential and the discrete variational X α methods within the local-density-functional formalism. An origin of the structural stability can be explained as follows: The electronegativities of Ga (As) dangling orbitals in the VB surface become smaller (larger) than those of the ideally sp3-hybridized orbital. This induces a charge transfer from the Ga to the As atom, to reduce unsaturated bonds at the surface. Further, the grey-scale schema of the calculated partial charge density agrees well with the images obtained from the most recent scanning tunneling microscopy experiments.