Variable stoichiometry surface reconstructions: New models for GaAs (111)(2×2) and (√19×√19)

The $(\bar1\bar1\bar1)$ surface of GaAs exhibits three stable reconstructions. Two are $(2\times 2)$, As stabilized and Ga stabilized respectively, and the third is $(\sqrt19\times\sqrt19)$. Transitions between these structures are obtained by variation of the experimental conditions. We propose new models for all of the above reconstructions, based on ab initio total-energy calculations and experimental information regarding surface composition.