First principles calculations of the vibrational properties of single and dimer F-type centers in corundum crystals

The present paper investigates the F-type centers in α-Al₂O₃ through their electronic and vibrational properties from first principle calculations using a periodic supercell approach, a hybrid functional, and all-electron Gaussian basis sets as implemented in the CRYSTAL17 code. Single F-type and dimer F₂-type centers related to oxygen vacancies in various charge states were considered. The defect-induced vibrational modes were identified and found to appear mainly in the low (up to 300 cm^-1) and high (above 700 cm^-1) frequency regions, depending on the defect charge. The perturbation introduced by the defects to the thermal nuclear motion in the crystal lattice is discussed in terms of atomic anisotropic displacement parameters. The calculated Raman spectra are discussed for the first time for such defects in α-Al₂O₃, suggesting important information for future experimental and theoretical studies and revealing deeper insight into their behavior.