Variable stoichiometry surface reconstructions: New models for GaAs(1¯1¯1¯) (2×2) and (√1¯9¯×√1¯9¯)

The (1¯ 1¯ 1¯) surface of GaAs exhibits three stable reconstructions. Two are (2×2), As stabilized and Ga stabilized respectively, and the third is (√19 × √19 ). 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.