The electronic and structural properties of CaS are calculated using full potential linearized augmented plane wave (FPLAPW) method within the local density approximation (LDA) and generalized gradient approximation (GGA) for the exchange-correlation energy. For both structures, NaCl structure (BI) and CsCl structure (B2), the obtained values for lattice parameters, Bulk modulus and its pressure derivative and transition pressure are in reasonable agreement with the experimental values. For electronic properties, the obtained value for band gap is smaller than the experimental value as well as other calculated results based on density functional theory. Engel and Vosko calculated an exchange potential for some atoms within the so-called optimize-potential model and then used the virial relation and constructed a new exchange-correlation functional (EV-GGA). We used that functional and obtained reasonable results for band gap. Finally we investigated the possibility for a third phase (Zinc Blend structure) for this crystal.

In this work, self-consistent calculations were performed for the nitrides Cr4N, FeCr3N and CrFe3N (in the perovskite structure) to investigate the influence on the electronic and magnetic properties of Fe4N due to the substitution of Fe atoms by Cr atoms. These calculations were done also for the ordered FeCr3 and CrFe3 compounds (in the FCC structure) to investigate the effects of inclusion of nitrogen in such alloys. The calculations (with FPLAPW+lo method) were performed at several lattice parameters in order to obtain the equilibrium volumes of these compounds. We also studied the behavior of the magnetism of these materials with pressure. The present calculations show that while FeCr3 is nonmagnetic, CrFe3 exhibits a ferrimagnetic order. On the other hand based on our calculations, FeCr3N and Cr4N are nonmagnetic contrary to CrFe3N that is ferrimagnetic. The analysis of density of states at equilibrium volume for CrFe3N shows that charge transfers to Fe atoms.

The electronic, and optical properties of rhombohedral Na0. 5Bi0. 5TiO3 nanostructured thin film have been studied by the first– principle approach. Density functional theory (DFT) has been employed to calculate the fundamental properties of the layers using full– potential linearized augmented plane– wave (FPLAPW) method. A 2×2×1 supercell was constructed with two vacuum slabs on top and down of the supercell. A geometry optimization was performed by PBE method. The optimized thin film structure was used for the intended calculations. As well, the reflectance, dielectric function, refractive index, of the thin film were calculated in the UV– vis region. Results showed very well consistency with the available experimental and theoretical reports. The optical conductivity also followed a similar trend to that of the dielectric constants. Energy loss function of the modeled compound was also evaluated. The evaluated loss function showed sharp peaks in UV-vis region and followed a steady state in IR, MIR and FIR parts of spectrum.

By means of ab-initio calculations on the basis of the FPLAPW method, we compared the energy loss near edge structure (ELNES) of carbon K edges in crystalline phenanthrene and its isomer, anthracene. In these two organic compounds, different non-equivalent carbon atoms can result in distinct K edge spectra due to the different carbon-carbon bond lengths, as a characteristic behavior of the molecular crystals. The smaller bond lengths push the ELNES features to the higher energies. In anthracene, the energy position of the edge-onset appears at lower energies due to its smaller electronic band gap. At the onset of the C K edge of anthracene, the strong splitting of the π * peak into two peaks is observable. Compared to the C K edge in anthracene, due to the slightly larger C– C bond length in phenanthrene, the peak position of the main σ structure has a red shift. The ELNES spectrum of crystalline phenanthrene includes electron transition of 1s carbon orbital to π * and σ * states. In anthracene, the first two intense features have contributions of π * orbitals. Consideration of the core-hole approximation by means of super-cells and the collection of semi-angles at magic value are essential to obtain reasonable ELNES spectra.