The electronic energy band structure, density of states (DOS) and charge density contour of KNbO 3 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-) band gap. From the DOS analysis as well as charge density studies, we find that the bonding between K and NbO 3 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.

The electronic structure and frequency dependent dielectric function () of rocksalt semiconductors PbSe and PbTe are investigated using the local density approximation ͑LDA͒ and the generalized gradient approximation as two different exchange and correlation approximations, within the full-potential linearized augmented plane-wave approach. Spin-orbit coupling has been incorporated in the study. The results are presented and compared with other recent calculations and experimental data. Structural properties are also obtained by means of calculations of total energy as a function of lattice parameters. The bulk structural parameters are sensitive to the choice of exchange and correlation approximation. The essential features of the band structure and density of states of PbSe and PbTe are reproduced by our calculations and agree quite well with available experimental results. The position of the minimum energy gap is correctly predicted, although the value of the gap is as usual, underestimated by the local density approximation with respect to the experimental data. This gap value is improved by the inclusion of the generalized gradient approximation. Also, we have calculated the real ͓ 1 ()͔ and imaginary ͓ 2 ()͔ parts of () for both compounds, in the framework of the LDA scheme for exchange and correlation. The inclusion of spin-orbit coupling leads to a richer structure in both 1 () and 2 (). The agreement with experimental results is satisfactory.

The structural properties, electronic energy band structure and some optical properties of the IV-VI compounds SnTe and GeTe are calculated using the full-potential linearized augmented plane wave method within the local density approximation and the generalized gradient approximation schemes. The calculations were also performed incorporating the effects of spin-orbit interactions. The calculated structural properties, energy band structures and optical spectra are in reasonable agreement with available experimental data. The response of the bandgaps to temperature and the presence of some prominent features in the energy bands as well as the dielectric functions are discussed.

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The optical properties of the antiperovskite superconductor MgCNi3 have been calculated using the full-potential linearized augmented-plane-wave method within the generalized gradient approximation scheme for the exchange–correlation potential. In order to fully elucidate the optical properties of MgCNi3, the dielectric function ε(ω), the reflectivity R(ω), the optical absorption coefficient I(ω), the optical conductivity σ(ω), the energy-loss function L(ω), the refractive index n(ω) as well as the extinction coefficient k(ω) were calculated. The prominent features in the spectra of the optical parameters are discussed.