Atomistic thermodynamic calculations are performed in order to examine the energetic% of self-diffusion in GaAs. An energetic assessment of the activation enthalpy of the saddle-point configuration of various modes of vacancy self-diffusion indicates second-nearest-neighbor hopping to be the energetically most favorable mechanism if vacancies are available in equilibrium concentrations. An assessment of the activation entropy indicates that normal diffusion prefactors of magnitude Do-10 -5-10

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... s, cm2 s -' are consistent with vacancy self-diffusion by second-nearest-neighbor hopping. It is proposed that self-diffusion experiments characterized by prefactors and activation energies of large magnitude, e.g., D"=: lo'-lo8 cm* s-' and E (I z 6 eV, involve processes in which surface vacancy generation is inhibited and self-diffusion is mediated by Frenkel pair generation.