Abstract
Cubic sodium niobate (NaNbO3) and tetragonal potassium niobate (KNbO3) crystals are studied using the Wien2k code. Lattice parameters are optimized by using generalized gradient approximations and results compared with existing experimental data. Electronic properties such as total and partial density of states (TDOS and PDOS), band structures have been calculated for both cubic and tetragonal phase of sodium and potassium niobate NaNbO3 and KNbO3 crystals, respectively. The indirect band gaps are observed for both phases. The electronic and optical properties of NaNbO3 and KNbO3 crystals are calculated by first principles using (GGA+U) approximations for both cubic and tetragonal phase. For both phases, the real and imaginary parts of complex dielectric function and thus optical constants such as absorption coefficient, energy loss function, reflectivity, refractive index, extinction coefficients and optical conductivity are calculated. The computed optical spectra of cubic and orthorhombic phases are compared with the experimental data and found good agreement with the results.