First-principles simulations of ferroelectric oxides

Problematics, choice of adequate calculational scheme and obtained results in the first-principles simulations of potassium niobate (in different ferroelectric phases), pure and Li-doped potassium tantalate, and lithium niobate are discussed. The ferroelectric instability, zone-center TO phonons, and crystallographic as well as optical characteristics of defects are concentrated on. For intrinsic defects, F centers (associated with O vacancies) and bound hole polarons (trapped by K vacancies) in KNbO₃ are discussed. In Li-doped KTaO₃, the interaction energies between substitutional impurities at adjacent K sites, which undergo different patterns of off-center displacements, are estimated. For LiNbO₃, the frequencies and eigenvectors of Γ TO phonons in all symmetry modes have been calculated.