DFT study of a single F center in cubic SrTiO3 perovskite

Various properties of a cubic phase of SrTiO3 perovskite containing single F centers (neutral oxygen vacancies), including energies of their formation and migration, were simulated using different formalisms of density functional theory (DFT) as implemented into CRYSTAL-2003 and VASP computer codes. The lattice relaxation around the F center was found to be sensitive to both shape and size of supercells used. The larger the supercell, the closer the defect energy level in the bandgap lies to the conduction band bottom. It approaches the optical ionization energy of 0.49 eV for 270-and 320-atom supercells, where the distance between neighboring defects increases up to four lattice constants. The defect bandwidth decreases ford these supercells down to 0.02 eV, i.e., the defect-defect interaction becomes negligible. Thus, the two different first-principles periodic approaches combined provide results that are converged with respect to the supercell size and correspond to a single defect limit. (c) 2005 Wiley Periodicals, Inc.