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In this work we have carried out a theoretical study of structural, electronic, elastic and optical properties for the three ternary compounds KGaS2, KGaSe2 and KGaTe2, using the pseudo-potential plane-wave scheme in the framework of the density functional theory. The obtained structural parameters are very close to the available experimental data. The analysis of band structure indicates semiconducting behaviour of these compounds with a direct bandgap. The mechanical properties of the considered KGaQ2 are investigated by predicting the single-crystal elastic constants and the macroscopic elastic parameters, such as the bulk modulus and shear modulus. Our results indicate that all the compounds are mechanically stable and both KGaSe2 and KGaTe2 exhibit a significant elastic anisotropy compared to KGaS2 compound. A set of frequency dependent optical parameters were calculated for incident radiation polarized in the [100], [010] and [001] crystallographic directions, including the complex dielectric function, the refractive index and the absorption coefficient. The studied materials show anisotropic in the optical properties, especially in the real and imaginary part of the dielectric function and in the refraction index. In addition, the obtained results show that our compounds absorb in the UV region. [ABSTRACT FROM AUTHOR]

First-principles total energy calculations were performed to study the stability of Rh2TMSn (TM=Cr, Mn and Fe) toward different magnetic ordering, ferromagnetic (FM), antiferromagnetic type I (AFM-I) and antiferromagnetic type II (AFM-II). We studied the effects of electron correlation on the magnetic stability of the compounds in both cubic and tetragonal structures using density functional theory (DFT) within the generalized gradient approximation (GGA) and GGA+U. The results show that the electron correlation has an important role in determining the magnetic stability of the compounds. The magnetic stability obtained from GGA+U agrees well with the available experimental results. The thermodynamic stability of the three compounds shows that all the compounds are stable in both cubic and tetragonal structures. Using the energy difference method, we were able to calculate the exchange interactions and estimate the Curie temperature of the Rh2MnSn compound in the cubic structure. The phonon dispersion curves were investigated for the first time using the linear-response approach in the context of density functional perturbation theory. The results show that all the compounds are dynamically stable in their predicted phases. [ABSTRACT FROM AUTHOR]

We used first-principles electronic structure calculations to investigate the structural, elastic, electronic and optical properties of the already synthesised NaAlSe2 and NaAlTe2 tetragonal compounds and the predicted NaAlO2 and NaAlS2 tetragonal systems. The computed structural parameters using the GGA-PBE approach are consistent with the corresponding experimentally determined ones. The calculated single-crystal and polycrystalline elastic moduli show that the studied materials are mechanically stable and of a weak stiffness with strong elastic anisotropy. Calculated band structures reveal that NaAlO2, NaAlS2 and NaAlSe2 are semiconductors with an indirect bandgap of Z-Γ type, while NaAlTe2 is of a direct bandgap of Z-Z type. The calculated frequency-dependent linear optical functions show that the title compounds are characterised by significant optical anisotropy and high optical absorption for a wide photon energy range in the UV spectrum. [ABSTRACT FROM AUTHOR]

We report the results of first-principles calculations regarding the structural parameters, elastic moduli, electronic structure and optical properties of the ternary rhombohedral layered compounds, KLaSe2 and RbLaSe2. These calculations were performed by employing the pseudo-potential plane-wave (PP-PW) method. Although the calculated structural parameters (a, c, V, c/a, bond-length d) using different exchange and correlation approximations are found in nice harmony with the available experimental data, the best agreement is obtained with the GGA-PW91 functional. The effect of the K–Rb substitution is noted very clearly on the degree of ionic bonding of the A–Se bond (A = K, Rb). The electronic band structure and the density of states (DoS) plots reveal the semiconducting characteristics of both compounds with an indirect bandgap energy, E g of about 2 eV. The mechanical stability of the ALaSe2 compounds is investigated for the first time by calculating the single-crystal elastic constants C i j using the stress-strain approach. In order to understand the linear optical properties of the studied systems, frequency-dependent polarized optical functions were computed for an energy range from 0.0 eV to 18 eV. Our calculated optical spectra reveal the isotropic nature of the optical properties of the ALaSe2 compounds. [ABSTRACT FROM AUTHOR]

The structural, mechanical, and electronic properties of scheelite-type CaWO4, SrWO4, and BaWO4 have been investigated using density-functional theory (DFT) within the generalized-gradient approximation (GGA). In particular, we have studied the effect of pressure in the crystal structure, elastic constants , elastic moduli (, and ), and elastic anisotropy. We have also investigated the band structure of the three studied compounds and the effect of pressure in their electronic bandgap. The obtained results compare well with experimental results regarding the high-pressure (HP) behavior of the crystal structure. The reported calculations allow us to get a better understanding of effects caused by compression on scheelite-type oxides and to predict the HP response of physical properties of importance for different technological applications. [ABSTRACT FROM AUTHOR]