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We compute the optical conductivity of 2D honeycomb crystals beyond the usual Dirac-cone approximation. The calculations are mainly based on the independent-quasiparticle approximation of the complex dielectric function for optical interband transitions. The full band structures are taken into account. In the case of silicene, the influence of excitonic effects is also studied. Special care is taken to derive converged spectra with respect to the number of k points in the Brillouin zone and the number of bands. In this way both the real and imaginary parts of the optical conductivity are correctly described for small and large frequencies. The results are applied to predict the optical properties reflection, transmission and absorption in a wide range of photon energies. They are discussed in the light of the available experimental data.

The electronic properties of PbTe nanocrystals (NCs) embedded in a CdTe matrix are investigated using an ab initio pseudopotential method and a repeated supercell approximation. The asymmetric distribution of polar dot-matrix interfaces leads to the presence of an electrostatic field within the NC region. The consequences of this field on the electronic properties of the dot-matrix system are discussed in detail. The resulting spatial separation of electrons and holes inside the NC region gives rise to a quantum-confined Stark effect. It influences the photoluminesence of the NCs. [ABSTRACT FROM AUTHOR]