Dynamic Nonlinear Optical Processes in Some Oxygen-Octahedra Ferroelectrics: First Principle Calculations

The nonlinear optical properties and electro-optic effects of some oxygen-octahedra ferroelectrics are studied by the density functional theory (DFT) in the local density approximation (LDA) expressions based on first principle calculations without the scissor approximation. We present calculations of the frequency-dependent complex dielectric function (omega) and the second harmonic generation response coefficient chi((2)) (-2 omega, omega, omega) over a large frequency range in tetragonal and rhombohedral phases. The electronic linear electro-optic susceptibility chi((2)) (-omega, omega, 0) is also evaluated below the band gap. These results are based on a series of the LDA calculation using DFT. The results for chi((2)) (-omega, omega, 0) are in agreement with the experiment below the band gap and those for chi((2)) (-2 omega, omega, omega) are compared with the experimental data where available.