Ab initio simulations on Frenkel pairs of radiation defects in corundum

Large scale first principles periodic calculations based on the density functional theory within the localized atomic orbital approach (DFT-LCAO) using the hybrid exchange- correlation potential B3PW have been performed in order to study the structural and electronic properties of radiation-induced Frenkel pairs O_i+V_O in corundum crystal. As an initial approach, we have used conventional 2x2x1 supercell for defective α-Al₂O₃ lattice containing 120 atoms. After relaxation of the ideal supercell structure, the optimized do_i-v_o distance has been found to be ∼4.5 Å while the formation energy of Frenkel pair has achieved 11.7 eV. The interstitial O_i atom, both single and a component of O_i+V_O pair, spontaneously forms a dumbbell with the adjacent atom in the regular oxygen sublattice (do_i-o 1.404 Å) with the induced charge -1.1 e. On the whole, possibilities of supercell model for proper description of Frenkel pairs with changing inter-defect distance and space orientation inside corundum crystal are rather limited. This is why the alternative cluster model must be developed for this aim.