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In this paper, some optical properties of pure and transition metal-doped (TM = Co and V) single-walled ZnO nanotubes (8,0) (SWZnONT(8,0)) such as, real and imaginary parts of the dielectric function, optical conductivity, refractive index and optical reflectivity, were investigated. The calculations have been performed within framework of the density functional theory (DFT) using the full potential linearized augmented plane wave (FP-LAPW) and the generalized gradient approximation (GGA). The results show that, optical properties of SWZnONT(8,0) are anisotropic, especially at low energies and this anisotropy at low energies increases with doping of V in SWZnONT(8,0) while the Co-doped SWZnONT(8,0) behaves like pure SWZnONT(8,0). Doping of ZnO nanotubes has a significant impact on the value of the dielectric constant, so that due to the presence of V atom, the dielectric constant is increased up to three times. Study of the imaginary part of the dielectric function and optical conductivity showed that the important energy range for absorption processes and optical transitions is low energy range to 15 eV. The optical transitions have been studied based on band structure and density of states. The results of the optical reflectivity showed that these nanotubes are transparent in a wide energy ranges which provide them for using in transparent coatings. In addition, due to the reported magnetic properties for V- and Co-doped ZnO nanotubes, these nanotubes are suitable for using in spintronics and magneto-optic devices. [ABSTRACT FROM AUTHOR]

Using the density functional theory (DFT) approach and full-potential linearized augmented plane waves (FP-LAPW) method, some of the electronic (density of states, band structure, and Fermi surfaces), magnetic (total and local magnetic moments, spin polarization, exchange constants), and optical properties (dielectric function, energy loss function, and refractive index) were investigated. The GGA + U approximation was used for the exchange-correlation term. The effect of hydrostatic pressure up to 20 GP has been studied on these properties. The results show that the In0.75Cr0.25P compound is a half metal with 100% spin polarization at the Fermi level and the increment of pressure does not change its half-metallic behavior. The half-metal gap achieved for this compound is variable between 1.38 and 1.5 eV. The interaction between Cr and P atoms in this compound is an anti-ferromagnetic type. It was observed that the total magnetic moment for this compound is about 3 μB. Local magnetic moments change with increasing pressure, but the total magnetic moment remains unaffected by increasing the pressure. Calculations of the optical properties of the In0.75Cr0.25P compound showed that the dominant mechanism for the low-energy photons is due to the induced free carriers of the Cr atom, and the optical properties of this compound, in particular the refractive index in the visible region, change with increasing pressure. [ABSTRACT FROM AUTHOR]

In this paper, some structural, electronic, and optical properties of c-Si 12 silicon allotrope was investigated based on the density functional theory approach. The results were compared to some of silicon allotropes. The structural results show that both the optimal cubic lattice constant and Si–Si bond length in the c-Si 12 structure are larger than the diamond-Si one, although the bulk modulus for the c-Si 12 structure is smaller than the diamond-Si and other Si allotrope structures. The electronic results indicate that c-Si 12 structure is a semiconductor with an indirect band gap having an energy distance about 0.187 eV between its indirect and direct band gaps. In the optical properties section, the dielectric function, energy loss function, refractive index, and reflectivity of the c-Si 12 structure were investigated and compared to the experimental data for the diamond silicon allotrope. Our results indicate that in the visible range, the optical absorption of the c-Si 12 structure is larger than the diamond-Si which implies the promising optical properties of the c-Si 12 structure and its advantage with respect to the diamond-Si one. • The obtained optimal lattice constant and Si-Si bond length for c-Si 12 structure are larger than diamond-Si one. • The bulk modulus for c-Si 12 structure is smaller than diamond-Si and all other Si allotropes. • The band gap of c-Si 12 is smaller than diamond-Si and other Si allotropes and silicon c-Si 12 allotrope is a semiconductor with an indirect band gap equal to 0.996 eV. • There is a distance about 0.187 eV between an indirect and direct band gaps. • The static dielectric constant of c-Si 12 is smaller than Diamond-Si and other Si allotropes. [ABSTRACT FROM AUTHOR]