In the present work, we investigate the structural, optoelectronic and thermoelectric properties of the YLi ₃ X ₂ ( X = Sb, Bi) compounds using the full potential augmented plane wave plus local orbital (FP-APW+lo) method. The exchange–correlation potential is treated with the generalized gradient approximation/local density approximation (GGA/LDA) and with the modified Becke–Johnson potential (TB-mBJ) in order to improve the electronic band structure calculations. In addition, the estimated ground state properties such as the lattice constants, external parameters, and bulk moduli agree well with the available experimental data. Our band structure calculations with GGA and LDA predict that both compounds have semimetallic behaviors. However, the band structure calculations with the GGA/TB-mBJ approximation indicate that the ground state of the YLi ₃Sb ₂ compound is semiconducting and has an estimated indirect band gap ( Γ<...

The electronic and optical properties of M ₂S (M = Li, Na, K and Rb) compounds in the cubic antifluorite structure have been calculated, using a full relativistic version of the full-potential augmented plane-wave plus local orbitals method based on density functional theory, within both the local density approximation (LDA) and the generalized gradient approximation (GGA). Moreover, the Engel–Vosko GGA formalism (EV-GGA) is applied so as to optimize the corresponding potential for band structure calculations. The calculated equilibrium lattices and bulk moduli are in good agreement with the available data. Band structure, density of states, electron charge density and pressure coefficients of energy gaps are given. Results obtained for band structure using EV-GGA are larger than those with LDA and GGA. It is found that the spin–orbit coupling lifts the triple degeneracy at the Γ point and the double degeneracy at the X point. The analysis of the electron charge density...

The elastic, electronic and optical properties of the filled tetrahedral semiconductor LiCdP have been investigated using the pseudo-potential plane wave method within the local density functional theory. A numerical first-principles calculation of the elastic constants was used to calculate C ₁₁, C ₁₂ and C ₄₄. The values of the sound velocities in different directions have been calculated. We derived the bulk and shear moduli, Young modulus and Poisson's ratio for ideal polycrystalline LiCdP. We estimated the Debye temperature of LiCdP from the average sound velocity. Band structures show that LiCdP is a direct band gap. The density of states and Mulliken charge populations analysis show that the Cd–P bond is typically covalent with a strong hybridization as well as that the Li–P bond has a significant ionic character. The variation of the gap versus pressure is well fitted to a quadratic function and a direct to an indirect ba...

The effect of high pressures, up to 30 GPa, on the structural, elastic and electronic properties of Ge X ₂O ₄, with X = Mg, Zn and Cd, were studied by means of the pseudo-potential plane waves method within the local density approximation for exchange and correlation. The results of bulk properties, including lattice constants, internal parameters, bulk modulus and derivatives are obtained. The band structures show a direct (Γ–Γ) band gap for the three compounds. All the calculated band gaps increase with increasing pressure and fit well to a quadratic function. The analysis of the density of states revealed that the lowering of the direct gap Γ–Γ from GeMg ₂O ₄ to GeZn ₂O ₄ to GeCd ₂O ₄ can be attributed to the p–d mixing in the upper valence band of GeZn ₂O ₄ and GeCd ₂O ₄. The elastic constants and their pressure dependence are calculated using t...

Using first-principles density functional calculations, the effect of high pressures, up to 30 GPa, on the structural, elastic and electronic properties of SiX ₂O ₄, with X = Mg, Zn and Cd, was studied by means of the pseudo-potential plane-waves method. We used both the local density approximation and the generalized gradient approximation to the exchange-correlation approximation energy. The results of bulk properties, including lattice constants, internal parameters, bulk modulus and derivatives, are obtained. The elastic constants and their pressure dependence are calculated using the static finite strain technique. We derived the bulk modulus, shear modulus, Young's modulus and Poisson's ratio for ideal polycrystalline SiX ₂O ₃ aggregates. We estimated the Debye temperature of SiX ₂O ₄ from the average sound velocity. Band structure, density of states and pressure coefficients of some gaps are also given. This is th...