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Abstract: Density functional calculations are performed to study the structural and electronic properties of technologically important Pb1−x Ca x S y Se1−y quaternary alloys. The calculations are based on the total-energy calculations within the full-potential augmented plane-wave (FP-LAPW) method. For exchange-correlation energy and corresponding potential, the generalized gradient approximation (GGA) by Perdew–Burke–Ernzerhof (PBE) and Engel–Vosko (EVGGA) have been used. We investigated the effect of composition on lattice constant, bulk modulus and band gap for pseudobinary as well as for quaternary alloys, which showed non-linear dependence on the composition x and y. The presented contour maps of energy band gap and lattice constants versus concentrations could be useful for designing new structures with the desired optical properties. In addition, the energy band gap and natural band offset of simple cubic Pb1−x Ca x S y Se1−y quaternary alloys lattice matched to PbS and SrS substrates are investigated. The obtained results show that the quaternary alloys of interest could be appropriate materials for designing heterostructures with desired optical and interfacial properties. [Copyright &y& Elsevier]

On the basis of ab initio calculations employing density functional theory (DFT), we investigate the structural, electronic, optical and thermodynamic properties of two binaries: PbS and PbSe in rock-salt structures. In addition, several compositions with various ordered structures of PbS1-xSex alloys were studied. The calculations were performed using the full potential linearized augmented plane wave (FP-LAPW) method within the generalized gradient approximation (GGA). Various quantities, such as equilibrium lattice constants, bulk modulus, band structures and refractive index for all Se-concentrations are presented. The microscopic origins of the gap bowing were explained by using the approach of Zunger and coworkers. On the other hand, the thermodynamic stability of these alloys was investigated by calculating the excess enthalpy of mixing ΔHm as well as the phase diagram. [ABSTRACT FROM AUTHOR]

Abstract: Using first-principle method, we investigate the structural, electronic, optical and thermodynamic properties of the strontium semiconductors Pb1− x Sr x S with 25%, 50% and 75% of Sr. The calculations are performed by using the full-potential linearized augmented plane wave (FP-LAPW) method. As exchange–correlation potential we used the generalized gradient approximation (GGA) of Perdew et al. The variation of the calculated equilibrium lattice constant versus concentration shows that a small deviation from Vegard’s law is clearly visible with downward bowing parameter equal to 0.009Å. The bulk modulus as a function of x for Pb1− x Sr x S alloy shows a significant deviation from the linear concentration dependence (LCD) with downward bowing equal to 6.62GPa. The different roles of structural and chemical effects on the gap bowing and its variation with composition are identified and discussed. In addition, density of states and optical properties were calculated and compared to the available experimental data and previous theoretical works. On the other hand, the thermodynamic stability of these alloys was investigated by calculating the excess enthalpy of mixing ΔH m as well as the phase diagram. [ABSTRACT FROM AUTHOR]

Abstract: The structural, electronic and thermodynamic properties of the SrS1– x O x ternary mixed crystals have been studied using the ab initio full potential linearized augmented plane wave (FP-LAPW) method within density functional theory. The effect of composition on lattice parameter, bulk modulus and band gap was investigated. The lattice constants from Vegard''s law and the bulk modulus from linear concentration dependence were observed for the alloys. The microscopic origins of the gap bowing were explained by using the approach of Zunger and co-workers. The thermodynamic stability of these alloys was investigated by calculating the excess enthalpy of mixing as well as the phase diagram. In addition to FP-LAPW method, the composition dependence of the refractive index and the dielectric constant was studied by different models. [Copyright &y& Elsevier]