First-principles calculation of the linear and nonlinear optical properties of LiTaO₃

Abstract

The linear and nonlinear optical (NLO) properties of the paraelectric and ferroelectric (FE) phases of lithium tantalate crystals were calculated using a first-principles approach based on density functional theory with the generalized gradient approximation. We present our results for the structural parameters, the imaginary and real parts of the frequency-dependent linear optical response, optical functions such as the spectral reflectivity, the absorption coefficient and the electron energy-loss spectrum. A simple scissors operator is applied to adjust the energy gap from calculations to match the experimental value. In the FE phase, we also study the NLO susceptibilities and calculate the NLO susceptibility tensor. LiTaO3 displays a good NLO effect. The results are compared with the theoretical calculations and available experimental data.

Electron Spectroscopy and the Electronic Structure of KNbO3: First Principle Calculations

“…Within the accuracy of our calculations, the values of the direct and indirect band gap are within 2.35 eV of each other in all phases except the rhombohedral one, where the minimum gap is 1.5 eV smaller than the first direct gap. Our results are in a good agreement with the previous calculation [14,17] performed at the experimental lattice parameters, with the exception of the rhombohedral phase (Table 2).…”

“…The agreement between our density of states (DOS) and the experimental spectrum is good [12][13][14][15][16][17][18][19]. The dispersion curve of the conduction bands at the theoretical equilibrium lattice parameters are reported in Fig.…”

“…In this section, we describe the evolution of the electronic structure of KNbO 3 in the structural and ferroelectric phase transitions in relation with the evolution of the symmetry of the crystal field. The results from vacuum ultraviolet (VUV) reflectivity experiments are reported in the literature for some ABO 3 compounds [12][13][14][15][16][17][18][19]. We furthermore give a comparison of the theoretical band structure of the valence and conduction bands in various phases.…”

“…Last, we report our results for the theoretical energy gap, and the energy gap values determined experimentally. Since ABO 3 ferroelectrics have been widely studied [12][13][14][15][16][17][18][19] we show in detail only the calculated band structures for KNbO 3 in different phases. The dispersion of the energy of the valence bands for the cubic (C), tetragonal (T) and rhombohedral (R) phases at the equilibrium lattice parameters are reported in Fig.…”

The nonlinear optical susceptibility and electro-optic tensor of ferroelectrics: first-principle study

“…The linear and nonlinear optical properties of ABO 3 [34][35][36] were theoretically studied by means of first-principles ¾ Unauthenticated Download Date | 5/10/18 2:43 PM calculations in the framework of density functional theory, based on the local density approximation [37] and the generalized gradient approximations (GGA) as implemented in the ABINIT code [11]. The self-consistent norm-conserving pseudopotentials are generated using the Troullier-Martins scheme [38] which is included in the Perdew-Wang scheme [39] as parameterized by Ceperly and Alder [40].…”