First-principles calculations of the nonlinear optical susceptibilities and Raman scattering spectra of lithium niobate

Nonlinear optical susceptibilities and nonresonant Raman scattering spectra of the ferroelectric phase of lithium niobate (LiNbO 3 ) are computed using a first-principles approach based on density functional theory and taking advantage of a recent implementation based on the nonlinear response formalism and the 2 n +1 theorem. Infrared reflectivity spectra of the ferroelectric phase of LiNbO 3 are also calculated. New assignments are proposed for the E-modes, clarifying a longstanding debate in the literature. In addition, it is shown that knowledge of the nonlinear optical susceptibility tensor of LiNbO 3 does not significantly alter the profile of its Raman spectra in a configuration where the longitudinal optic modes are involved.