First-principles study of vibrational properties of lithium niobate

We present first-principles calculations of the well-known non-linear optical material LiNbO₃. Starting from the ground state properties, e.g. band structure of the stochiometric system, we use density functional perturbation theory to find the vibrational modes. Since LiNbO₃ is a polar ferroelectric material that involves long range interactions, we use the Ewald summation to add the coulombic interaction to the dynamical matrix formalism. The transverse and longitudinal modes are in good agreement with the other ab-initio calculations, as well as the spectroscopic measurements.
In addition, we calculate the relative stability of various intrinsic and extrinsic defects in this material and study their effect on the electronic, optical, and vibrational properties of this system. Achieving desirable defect properties is essential for improving the photorefractive response of LiNbO₃.