Theoretical study of the electronic structure, chemical bonding and optical properties of KNbO3 in the paraelectric cubic phase

The electronic energy band structure, density of states (DOS) and charge density contour of KNbO3 in the paraelectric cubic phase have been studied using the full-potential linearized augmented plane wave method within the generalized gradient approximation for exchange and correlation. The band structure shows an indirect (R-Gamma) band gap. From the DOS analysis as well as charge density studies, we find that the bonding between K and NbO3 is mainly ionic while that between Nb and O is covalent. We have also reported results on the pressure variation of the energy gap of this compound and found that the band gap increases with increasing pressure. In order to understand the optical properties of the perovskite, the real and imaginary parts of the dielectric function, reflectivity, absorption coefficient, optical conductivity, electron energy-loss function, refractive index and extinction coefficient were calculated. The general profiles of the optical spectra were analysed and origins of the structures discussed.