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We have investigated the optical properties of gallium arsenide (GaAs) in the photon energy range 0.6-6.0 eV. We obtained a refractive index which has a maximum value of 5.0 at a photon energy of 3.1 eV; an extinction coefficient which has a maximum value of 4.2 at a photon energy of 5.0 eV; the dielectric constant, the real part of the complex dielectric constant has a maximum value of 24 at a photon energy of 2.8 eV and the imaginary part of the complex dielectric constant has a maximum value of 26.0 at a photon energy of 4.8 eV; the transmittance which has a maximum value of 0.22 at a photon energy of 4.0 eV; the absorption coefficient which has a maximum value of 0.22 10 8 m 1 at a photon energy of 4.8 eV, the reflectance which has a maximum value of 0.68 at 5.2eV; the reflection coefficient which has a maximum value of 0.82 at a photon energy of 5.2 eV; the real part of optical conductivity has a maximum value of 14.2 10 15 at 4.8 eV and the imaginary part of the optical conductivity has a maximum value of 6.8 10 15 at 5.0 eV. The values obtained for the optical properties of GaAs are in good agreement with other results.

In this work, we report about the electronic and elastic properties of crystalline poly(3,4-ethylenedioxythiophene), known as PEDOT, in an undiluted state, studied in the framework of semilocal DFT, using the PBE and PBEsol exchange-correlation functional and PAW pseudopotentials. Contrary to previous molecular dynamics simulations, our calculations revealed that the most stable state structure of pristine PEDOT is monoclinic. We calculated the 13 independent elastic constants and the elastic compliance which enables us to establish other elastic properties of pristine PEDOT; the Pugh's ratio and the Vicker's hardness computed with PBE and PBEsol are in good agreement with each other. Finally, we compute the directional elastic modulii and found remarkable differences between different DFT functionals.

Abstract. Here we report the reflection coefficient and optical conductivity of gallium nitride (GaN). The reflection coefficient obtained in the photon energy range 2-10 eV shows five distinct peaks at photon energies 3.5, 5.0, 7.0, 8.0, and 9.0 eV. It was observed that the reflection coefficient has its highest value 0.54 at the photon energy 7.0 eV. Variation of the real part of optical conductivity with photon energy shows five distinct peaks at photon energies 3.5, 5.0, 7.0, 8.0, and 9.0 eV. It was observed that the real part of optical conductivity has the maximum value 5.75·10 15 for the photon energy 7.0 eV, and it decreases until coming to zero at 10.0 eV. The peaks indicate regions of deeper penetration of electromagnetic waves, and they also show high conductivity. The imaginary part of optical conductivity obtained for GaN in the photon energy range 2.0 to 10.0 eV shows five distinct peaks at photon energies 3.5, 5.0, 7.0, 8.0, and 9.0 eV. It was observed that it has a minimum value of -6.46·1015 for the photon energy 8.0 eV and a maximum value at -1.2·10 15. This implies that there is a reduction in conductivity of GaN, and likewise, reduction in the propagation of electromagnetic waves in this region.

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