Predictions on structural, electronic, optical and thermal properties of lithium niobate via first-principle computations

In this work, we present our predictions on lithium niobate LiNbO3 concerning its structural, electronics, thermal and optical properties. These predictions are done by means of first-principles calculations performed within the full potential linearised augmented plane wave plus local orbital (APW + lo) approach designed within the density functional theory (DFT). The generalised gradient approximation (GGA), to appraise the electron exchange-correlation, parameterised by Perdew-Burke and Ernzerhof is implemented. From our calculations, optimised results for lattice parameters are obtained by optimising the volume of the simulated hexagonal unit cell of lithium niobate. Our computed results for structural parameters are consistent with the data reported in the literature. On the other hand, for the better description of the band structure/energy band gap, calculations of the band structure are performed, as well, at the level of GGA-mBJ with and without the inclusion of spin-orbit coupling effect. Our calculations of electronic band structure and density of states (DOS) show that LiNbO3 is a direct and wide bandgap material as the transition is found to be along (Gamma-Gamma) symmetry direction with numerical value about 4.084 eV. However, no significant influence of the spin-orbit coupling (SOC) is noted on the band gap energy. Furthermore, optical parameters like dielectric function, anisotropy, refractive index, birefringence, extinction and absorption coefficients, optical conductivity and the energy loss spectrum (EELS) have also been calculated for an energy range, 0-40 eV. Similarly, by employing the 'Debye Quasi-Harmonic Model' crucial thermal parameters of the LiNbO3 are predicted.