Reconstruction of Semiconductor Surfaces: Buckling, Ionicity, Andπ-Bonded Chains

Buckling distortions, widely thought to lower the total energy of semiconductor surfaces, are shown to actually raise the energy of Si(111)-2\ifmmode\times\else\texttimes\fi{}1. The $\ensuremath{\pi}$-bonded-chain reconstruction, in contrast, stabilizes the surface, even relative to recently proposed magnetic reconstructions. Calculations for GaAs(110) reveal that the large charge transfers associated with buckling can stabilize the surface of heteropolar semiconductors, by returning the ions of the bulk to neutral atoms at the surface. These conclusions are based on self-consistent pseudopotential calculations.