Raman scattering intensities in BaTiO3 and PbTiO3 prototypical ferroelectrics from density functional theory

Nonlinear optical susceptibilities and Raman scattering spectra of the ferroelectric phases of BaTiO3 and PbTiO3 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 2n + 1 theorem. These two prototypical ferroelectric compounds were chosen to demonstrate the accuracy of the Raman calculation based both on their complexity and their technological importance. The computation of the Raman scattering intensities has been performed not only for the transverse optical modes, but also for the longitudinal optical ones. The agreement between the measured and computed Raman spectra of these prototypical ferroelectrics is remarkable for both the frequency position and the intensity of Raman lines. This agreement presently demonstrates the state-of-the-art in the computation of Raman responses on one of the most complex systems, ferroelectrics, and constitutes a step forward in the reliable prediction of their electro-optical responses.