Structural models for the √19x√19 reconstruction of the GaAs((1)over-bar(1)over-bar(1)over-bar) surface and their relative stabilities

We present a theoretical study of the relative formation energies for possible models of the root 19 x root 19 reconstruction found under Ga-rich growth conditions at the GaAs((111) over bar) surface. The energetically most favourable model has fourfold-coordinated Ga atoms on the surface, exhibiting metallic bonding character. This structure differs as regards the electron-counting rule (ECR) from the well accepted models for the (100), (110) and (111) surfaces of GaAs. Our results suggest that it is still possible to explain the stability of the metallic ((111) over bar) surface with a rule similar to the ECR.