Résumé: The present study reports the properties of pressure-induced phase transition, electronic and optical of phosphides ­XSiP 2 under pressure in chalcopyrite, sodium chloride (rock salt), and Wurtzite phases. The study shows the chalcopyrite phase as the most stable phase among the other studied phases. The obtained structural parameters in the chalcopyrite and rock-salt phases reasonably agree with the literature. The computed band structures revealed a semiconductor behavior in chalcopyrite structure and metallic behavior for rock- salt and wurtzite structures. In the energy range of 0 to 30 eV, optical parameters such as the real and imaginary parts of the dielectric constant, refractive index, and reflectivity are calculated and compared with existing data. Our optical properties findings are predictive for the rock-salt and wurtzite phases. Since no results are available in the literature, these results may serve as references for other theoretical and experimental studies. Method The calculations are performed by employing the “full-potential linearized augmented plane wave (FP-LAPW) method within density functional theory (DFT).”

Résumé: This study primarily focuses on examining the structural, electronic, optical, and elastic characteristics of the ternary alloys B-Ga, Bi. To thoroughly investigate these attributes, we conducted calculations using the "full potential linearized augmented plane wave (FP-LAPW)" method within the framework of "density functional theory (DFT)". Our

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Résumé: In this investigation, we employ density functional theory with the generalized gradient approximation of Wu-Cohen and the modified Beck-Johnson approach. Our focus is on examining the structural, electronic and ther- modynamic properties of temary chalcopyrite CdXP, (X: Si and Sn) compounds. Our computed results of ternary

Résumé: Ab initio calculations were carried out on the structural, electronic, thermal and optical pro- perties of the binary compounds BP, BAs, BN and BP in the different phases: zinc blende (B3),

Résumé: In the course of this investigation, we performed ab initio calculations. The investigation systematically explored the physical features of chalcopyrite-phase BeXAs2 (X=Sn and Ge). Total energy calculations incorporated the Wu-Cohen generalized gradient approximation

Résumé: The PP-LAPW method is used to examine the physical properties of Te-Pd binary intemetallic compounds. The calculated formation enthalpies indicate that Fed and FePdy compounds are thermodynamically stable in L and L1 phases, respectively, and the ferromagnetic Pd can be formed in a goal structure with a small negative formation enthalpy. The elastic coefficients and their related parameters show that all compounds are mechanically stable and ductile in nature. The Fed-Llo is the harder compound and PePd-Z1 exhibit the highest anisotropy. The band structure, the TDOS pofle and the charge density distribution show that these compounds am ferromagnetic with a metallic character and covalent-metallic bonds. The PDOS shows that the Pd-4d and e-data are dominant, and the asymmetry of P-3d state is behind the system strong spin po ladiation. The calculated magnetic moments agree well with previous thecotical reults. The thermodynamic parameters are determined using the qua-hole Debye model

Résumé: This research explored the physical properties of AuMTe 2 (M = Ga, In) chalcopyrite compound. We employ the full-potential linearized augmented plane wave (FP-LAPW) method in combination with the Tran-Blaha modified Becke–Johnson potential (TB-mBJ) as well as the generalized gradient approximation (GGA-PBE(96)), local density approximation (LDA) and Wu–Cohen generalized gradient approximation (WC-GGA) for the exchange–correlation potentials to analyze the structural, electronic and optical properties. The results are presented for lattice constant, bulk modulus, its pressure derivative, density of state (DOS) and optical properties. The structural and electronic outcomes obtained in this study align well with existing theoretical data. Our investigation revealed that the studied compounds exhibit a direct band gap, with average energy gaps of order of 0.281 eV for AuGaTe 2 and 0.092 eV for AuInTe 2 compounds, respectively. Optical properties, encompassing reflectivity R(w), absorption coefficient a(x), refractive index n(x), optical conductivity r(x), extinction coefficient k(x) and energy loss function L(x) are determined from real and imaginary parts of the computed dielectric function within the frameworks of the modified Becke–Johnson plus PBE- GGA(96), LDA and WC-GGA exchange–correlation potentials. The computed optical properties reveal minimal energy loss and reflectivity, alongside satisfactory absorption capability and optical conductivity within the infrared and visible spectral regions. These findings indicate potential applications in fields such as infrared absorption technologies and optoelectronic industries. This marks the initial quantitative theoretical forecast of the optical properties for these chal- copyrite compounds, necessitating experimental confirmation.

Résumé: Understanding the physical properties of a material is crucial to know its applicability for practical applications. In this study, we investigate the phase stability, elastic, electronic, thermal, and optical properties of the ternary alloying of the scandium and yttrium nitrides ­(Sc 1-x Y x N) for different compositions. To do so, we apply a “density functional theory (DFT)” based scheme of calculations named as “full potential (FP) linearized (L) augmented plane wave plus local orbitals (APW + lo) method” realized in the WIEN2k computational package. At first, the phase stability of the investigated compositions of the mentioned alloy is determined. The analysis of our calculations shows that ­Sc 1-x Y x N alloy is stable in rock salt crystal structure for all investigated compositions. Next to that, the elastic properties of the rock-salt phase of the studied ternary alloy ­Sc 1-x Y x N at all above said compositions were done at the level of “Wu-Cohen generalized gradient approximation (Wu-GGA)” within DFT. However, Trans-Blaha (TB) approximation of the “modified Becke-Johson (mBJ)” potential is also used in combination with Wu-GGA where the thermal properties are calculated at the level of the “quasi-harmonic Debye model.” The obtained results for the absorption coefficients, and optical bandgap, represent that the title alloy may be a suitable candidate for the applications in optoelectronic devices.

Résumé: Understanding the physical properties of a material is crucial to know its applicability for practical applications. In this study, we investigate the phase stability, elastic, electronic, thermal, and optical properties of the ternary alloying of the scandium and yttrium nitrides ­(Sc 1-x Y x N) for different compositions. To do so, we apply a “density functional theory (DFT)” based scheme of calculations named as “full potential (FP) linearized (L) augmented plane wave plus local orbitals (APW + lo) method” realized in the WIEN2k computational package. At first, the phase stability of the investigated compositions of the mentioned alloy is determined. The analysis of our calculations shows that ­Sc 1-x Y x N alloy is stable in rock salt crystal structure for all investigated compositions. Next to that, the elastic properties of the rock-salt phase of the studied ternary alloy ­Sc 1-x Y x N at all above said compositions were done at the level of “Wu-Cohen generalized gradient approximation (Wu-GGA)” within DFT. However, Trans-Blaha (TB) approximation of the “modified Becke-Johson (mBJ)” potential is also used in combination with Wu-GGA where the thermal properties are calculated at the level of the “quasi-harmonic Debye model.” The obtained results for the absorption coefficients, and optical bandgap, represent that the title alloy may be a suitable candidate for the applications in optoelectronic devices.

Résumé: In the current work, using the full-potential linearized augmented plane wave (FP-LAPW) method implemented in the Wien2k code and framed within density functional theory (DFT), we present a theoretical analysis of the structural, elastic, electronic, and optical properties of binary compounds CaX (X = S, Se), and ternary alloys Ca 0.75 Cd 0.25 X (X = S, Se). We employ the Wu-Cohen approximation to estimate the exchange-correlation po­ tential. This approximation enables us to accurately determine the elastic and structural properties of the studied materials. Furthermore, we enhance the accuracy of our electronic structure calculations by incorporating the modified Becke Johnson (mBJ) potential. Our calculations for the structural, elastic, electronic and optical pa­ rameters of the binary compounds are compared with previously reported studies and are found to be consistent with the available data in the literature. We observe that our materials are semiconductors characterized by an indirect band gap energy (Γ-X) for CaX and (M-Γ) for Ca 0.75 Cd 0.25 X. Furthermore, the outcomes of our com­ putations demonstrate that our materials exhibit brittleness, as determined by evaluating the elastic constants and corresponding elastic moduli. To our knowledge, the ternary alloys are investigated for the first time and the obtained results are predictions and still need to undergo experimental validation.

Résumé: In this study, for the concentrations of x=0.0, 0.25, 0.5, 0.75 and 1.0, the calculations of the physical properties of GaP 1–x N x mixed alloys are presented. To perform these calculations, we employ WIEN2k computational code based on the approach of full-potential linearized augmented plane wave plus local orbital FP(L(APW?lo)), which is framed within density functional theory. At first, at the level of the WC-GGA scheme, the phase stability of the GaP 1–x N x alloys in their sodium chloride (B1), zinc-blende (B3) and wurtzite (B4) structures were analysed. The analysis of our results shows that GaP, GaP 0.75 N 0.25 , GaP 0.5 N 0.5 and GaP 0.25 N 0.75 are stable in B3 crystal structure, whereas GaN is found to be stabilized in wurtzite structure. Moreover, for each concentration, the pressure-induced phase transition of B3 and B4 structures to B1 structure is also explored. On the other hand, the calculations of the band structures show changeover of indirect band gap energy for GaP with energy gap 2.23 eV to direct band nature for GaN with band gap energy 3.183 eV. Likewise, the optical properties are explored for the energy range of 0.0–40 eV. The investigations of the thermodynamic properties, for example, entropy, Debye temperature, specific heat are carried out at the level of the ‘quasi-harmonic Debye model’. Moreover, the effect on the thermodynamic properties by temperature and pressure is also predicted. The results obtained for band gap energy as well as the optical absorption coefficients endorse that the investigated compositions of the alloys are very right for infrared to visible region optoelectronic applications.

Résumé: In this work, a comprehensive study concerning the physical properties of ternary alloys system ­(AlP 1−x Bi x ) at different concentrations is presented. The obtained results from our first-principle calculations are compared with previously reported studies in the literature and discussed in detail. Our computed results are found in a nice agreement where avail- able with earlier reported results. Electronic band structures at the above-mentioned concentrations are also determined. Likewise, the impact of the varying temperature and pressure on Debye temperature, heat capacity, and entropy is analyzed as well. Furthermore, elastic constants and related elastic moduli results are also computed. Our results show that alloys are stable and found to be in brittle nature. This is the first quantitative study related to ternary alloys ( ­ AlP 1−x Bi x ) at mentioned concentrations. We soon expect the experimental confirmation of our predictions. Method The calculations are performed, at concentrations x=0.0, 0.25, 0.5, 0.75, and 1.0 by using the “full potential (FP) linearized (L) augmented plane wave plus local orbital (APW+lo) method framed within density functional theory (DFT)” as recognized in the “WIEN2k computational code”. The “quasi-harmonic Debye model” approach is employed to determine the thermal properties of the title alloys.

Résumé: In this research work, first-principles computational study is performed on the structural, elastic, thermal, magnetic, electronic, and thermoelectric properties of the ternary Heusler compound Co 2 MnGe in its cubic phase. For this purpose, the “full potential linearized augmented plane-wave FP-L(APW + lo)” approach realized in the WIEN2k code is employed. To determine total energy, the exchange–correlation energy/potential part is treated within the “Perdew–Burke–Ernzerhof (PBE)” parameterized approach of “generalized gradient approximation (GGA) and modified Becke–Johnson (mBJ)” schemes. The magnetic phase stability was predicted via quantum mechanically total energy calculations for both non-magnetic and magnetic phases. Our obtained results for total energy show that the title material is stable in the ferromagnetic phase. The analysis of the profile of density of states (DOS), band structure plots, and the calculations of spin magnetic moment endorse the semi-metallic nature of the title compound. Calculations of the elastic constants, C ij , and results of the elastic moduli, such as bulk modulus (B ), shear modulus (G), Young modulus (E ), Poisson ratio (ν), and ratio B /G, are reported and analyzed as well. Gibbs computational code based on the “quasi-harmonic Debye model” is used to explore thermal properties, whereas parameters to understand the thermoelectric behavior, BoltzTrap code based on Boltzmann theory for transport properties is applied. Besides that, the chemical potential effect on the Seebeck coefficient and power factor is also analyzed at temperatures 300, 600, and 900 K. The results of thermoelectric parameters of the title Heusler compound, for the spin-down channel, are found good; hence, the obtained results highlight the title compound as a potential candidate for thermoelectric devices.

Résumé: The structural, electronic, optical and thermal properties of chalcopyrite LiAlTe 2 are studied using the full potential linearized augmented plane wave (FP-LAPW) method framed within density functional theory (DFT). The Wu-Cohen generalized gradient approximation (WC-GGA) was used as exchange-correlation potential to calculate the structural properties. Furthermore, the Tran and Blaha modified Becke-Johnson (mBJ) functional was also employed to compute the electronic and optical properties in order to get best values. The structural parameters at equilibrium are in good agreement with previous experimental and theoretical calculations. The band structures and density of states are calculated and it is found that LiAlTe 2 compound is a direct band gap (Ŵ-Ŵ) semiconductor. In addition, the optical properties such as dielectric function, refractive index, reflectivity and absorption coefficient are calculated for photon energies up to 25 eV. This study on the optical properties has also been enriched by the introduction of the analysis of birefringence and anisotropy for this material. The calculated values of all parameters are compared with the available theoretical data where a reasonable agreement has been obtained. The study of the material properties at high temperatures and pressures is very important to understand the behavior of a material in severe conditions, so the temperature and pressure dependencies of unit cell volume, bulk modulus, Debye temperature and specific heat capacities are obtained at different temperatures (0−1000 K) and pressures (0−8 GPa) using the quasi-harmonic Debye model. To our knowledge this is the first theoretical prediction of the thermal properties for LiAlTe 2 compound and still awaits experimental confirmations. We have included the spin-orbit interaction (SOI) in our calculations which is known to have significant influence on the electronic and optical properties when heavy elements are present. A weak effect is observed for the studied compound.

Résumé: The structural, electronic, elastic, and optical properties of ternary alloys ­G aP x Bi 1−x as a function of phosphorus concentration were studied using ab initio calculations. We have used the full-potential linearized augmented plane wave method–based density functional theory. The potentials have been described by the generalized gradient and modified Becke-Johnson approximations. Results on lattice parameters, energy band gap, bulk modulus, elastic, and optical properties are reported. They are in good agreement with available theoretical and experimental data. Moreover, the dependence of structural and electronic properties on the composition has been analyzed. A deviation from linearity is observed for the lattice constant and the bulk modulus. In addition, the elastic constants and moduli were calculated and used to examine the mechanical stability. Both parts of dielectric-function and other optical parameters have been analyzed.

Résumé: In this research work, first-principles computational study is performed on the structural, elastic, thermal, magnetic, electronic, and thermoelectric properties of the ternary Heusler compound Co 2 MnGe in its cubic phase. For this purpose, the “full potential linearized augmented plane-wave FP-L(APW + lo)” approach realized in the WIEN2k code is employed. To determine total energy, the exchange–correlation energy/potential part is treated within the “Perdew–Burke–Ernzerhof (PBE)” parameterized approach of “generalized gradient approximation (GGA) and modified Becke–Johnson (mBJ)” schemes. The magnetic phase stability was predicted via quantum mechanically total energy calculations for both non-magnetic and magnetic phases. Our obtained results for total energy show that the title material is stable in the ferromagnetic phase. The analysis of the profile of density of states (DOS), band structure plots, and the calculations of spin magnetic moment endorse the semi-metallic nature of the title compound. Calculations of the elastic constants, C ij , and results of the elastic moduli, such as bulk modulus (B ), shear modulus (G), Young modulus (E ), Poisson ratio (ν), and ratio B /G, are reported and analyzed as well. Gibbs computational code based on the “quasi-harmonic Debye model” is used to explore thermal properties, whereas parameters to understand the thermoelectric behavior, BoltzTrap code based on Boltzmann theory for transport properties is applied. Besides that, the chemical potential effect on the Seebeck coefficient and power factor is also analyzed at temperatures 300, 600, and 900 K. The results of thermoelectric parameters of the title Heusler compound, for the spin-down channel, are found good; hence, the obtained

Résumé: The structural, phase stability, elastic and electronic properties of Sb-doped BBi have been systematically investigated in the zinc blende phase by means of the first-principle approach based on the density functional theory (DFT). The structural and elastic properties were computed by using the generalized gradient approximation proposed by Wu and Cohen (WC-GGA). Specifically, the calculated basic structural parameters, such as the lattice constant and bulk modulus, are in good agreement with the existing experimental mea- surements and theoretical calculations. The phase stability of BBi 1-x Sb x alloys in the zinc blende and rock salt phases has been investigated with the determination of the transition pressures (Pt) from the zinc blende (B3) to the rock salt (B1) phase. The electronic band structures were determined using the Tran–Blaha-modified Johnson functional. Furthermore, we investigated the mechanical properties and anisotropic behavior of the BBi 1-x Sb x alloys.

Résumé: The structural, elastic, mechanical, optoelectronic, and thermodynamics properties of InP, InSb, and their mixed ternary alloys, InP 1-x Sb x , in their zinc blende structure for 0
x
1, are studied. The “full potential linearized augmented plane wave (FP-LAPW) method framed within density functional theory (DFT)" as realized in WIEN2k computational code is employed for all calculations. The results of elastic constants for simulated structures of InP 1-x Sb x alloys are the first time computed in this study. The results of the elastic constants showed that the InP 1-x Sb x alloys, for all compositions of x, are brittle and mechanically stable above and beyond showing the strong anisotropic character as well. On the other hand, the ob- tained results of InP 1-x Sb x for lattice parameters, bulk modulus, and band gap energy exhibit their nonlinear character. Also, the optical properties are determined at the level of the mBJ scheme for an energy range from 0 to 40eV. However, the “quasi-harmonic Debye model” is used to investigate the thermodynamics properties for example Debye temperature, specific heat, entropy, and their depen- dence on pressure, and the temperature is also analysed for the mentioned alloys. Our computed results for optical band gap and absorption coefficients expose these alloys as suitable candidate materials for optoelectronics applications in the infrared as well as in the visible region.

Résumé: In this work, the structural and electronic properties of the ternary chalcopyrite semiconductors ZnSiAs 2 and ZnSnAs 2 and their related ZnSi 1 – x Sn x As 2 quaternary alloys are presented. The density func- tional theory (DFT) within full-potential linearized augmented plane wave is employed. To treat the exchange–correlation potential for the total energy calculations, the generalized gradient approximation by Wu–Cohen is used. Additionally, the modified Becke–Johnson potential approximation has also been used to improve the underestimated band gap. For the ternary compounds, the optimized equilibrium structural parameters (a, c, and u) are in good agreement with available theoretical and experimental data. ZnSi 1 – x Sn x As 2 alloys are direct band gap semiconductors. The effects of the composition x on lattice parameters, bulk mod- ulus, and band gaps are investigated. A quadratic fit of the lattice parameter, bulk modulus, and band gap is performed, where a non-linear variation with the composition is found. A decrease in the band gap is observed with an increasing Sn content.

Résumé: The structural stability and optoelectronic properties of the ternary Ba 1−x Be x S alloys along with the pure binary compounds BaS and BeS in the rock-salt (B1) and zinc-blende (B3) phases were investigated by the density functional theory (DFT) within the full-potential linearized augmented plane wave (FP-LAPW) method implemented in the Wien2k package. The generalized gradient approximation of Wu and Cohen (WC-GGA) was used for the exchange-correlation potential (V xc ) to compute the equilibrium structural parameters, lattice constant (a), and bulk modulus (B). In addition to the GGA approach, the modified Becke-Johnson potential of Tran and Blaha (TB-mBJ) scheme coupled with the spin-orbit interaction was used to calculate the band gap energies. Results reveal that BaS, Ba 0.75 Be 0.25 S, and Ba 0.5 Be 0.5 S compounds are stable in the rock-salt phase, while Ba 0.25 Be 0.75 S and BeS are found to be stable in the zinc-blende phase. The computed results for the band structures and optical constants are compared with other available theoretical calculations and experimental measurements.

Résumé: In this study, structural properties of the zinc-blende (B3) phase and its transition pressure and other important physical properties of GaAs, GaSb compounds, and their mutual alloys for x = 0.25, 0.5 and 0.75 concentration of the Sb are investigated. The computations are carried out using a full-potential (FP) linearised (L) augmented plane wave plus local orbital method (APW + lo) designed within the density functional theory (DFT). The calculations of the structural properties are done at the level of Wu-Cohen generalized gradient approximation (WC-GGA), Perdew-Burke-Ernzerhof approximation (PBE-GGA), as well as Perdew-Wang local density ap- proximation (PW-LDA). Whereas the elastic constants are calculated using WC-GGA. However, to obtain consistent results of the electronic properties, the calculations are carried out by em- ploying Engle-Vosko (GGA) and Tran-Blaha (TB) modified Becke-Johnson (mBJ) potential ap- proach. For each concentration, the pressure-induced phase transition of zinc blende (B3) to rocksalt (B1) structure is investigated. Our band structure calculations show that the alloys are of direct band nature with bandgap energies in a range from 1.559 eV to 0.861 eV with increasing Sb. Furthermore, optical parameters at the level of the mBJ approach are also determined over a range from 0.0 eV to 40.0 eV. From the analysis of our obtained results of enthalpy of mixing, ΔH m , and other properties, it is found that the alloys under investigation are stable over a wide range, and suitable candidates for photovoltaic applications over a wide range of the solar spectrum including visible region.

Résumé: In this work, we present our predictions on lithium niobate LiNbO 3 concerning its structural, electronics, thermal and optical properties. These predictions are done by means of first-principles calculations performed within the full potential linearised augmented plane wave plus local orbital (APW + lo) approach designed within the density functional theory (DFT). The generalised gradient approximation (GGA), to appraise the electron exchange– correlation, parameterised by Perdew–Burke and Ernzerhof is implemented. From our calculations, optimised results for lattice parameters are obtained by optimising the volume of the simulated hexagonal unit cell of lithium niobate. Our computed results for structural parameters are consistent with the data reported in the literature. On the other hand, for the better description of the band structure/energy band gap, calculations of the band structure are performed, as well, at the level of GGA-mBJ with and without the inclusion of spin–orbit coupling effect. Our calculations of electronic band structure and density of states (DOS) show that LiNbO 3 is a direct and wide bandgap material as the transition is found to be along (Γ-Γ) symmetry direction with numerical value about 4.084 eV. However, no significant influence of the spin–orbit coupling (SOC) is noted on the band gap energy. Furthermore, optical parameters like dielectric function, anisotropy, refractive index, birefringence, extinction and absorption coefficients, optical conductivity and the energy loss spectrum (EELS) have also been calculated for an energy range, 0–40 eV. Similarly, by employing the ‘Debye Quasi-Harmonic Model’ crucial thermal parameters of the LiNbO 3 are predicted.

Résumé: The full potential linearized augmented plane wave (FP-LAPW) method was used to investigate the ground states as well as the mechanical, electronic, magnetic and optical properties of M 3 V (M: Pd, Pt) compounds. The generalized gradient approximation (GGA) of Perdew-Burke and Ernzerhof (PBE-GGA) is employed to treat the exchange-correlation potential for all the calculations except for structural properties where both Wu and Cohen generalized gradient approximation (WC-GGA) and Perdew and Wang local spin density approximation (LSDA) have been added. The cohesive energies, the formation enthalpies and the densities of states at the Fermi level N(E F ) show that the D0 22 structure is more stable than D0 23 and L1 2 . The lattice parameter and bulk modulus results agree well with the available experimental measurements and theoretical predictions. The elastic and mechanical properties are predicted and show that both compounds exhibit ductile behavior. Furthermore, our calculations of Debye and melting temperatures are in good agreements with experimental results reported in the literature. The densities of states (DOS) show that strong d-d hybridization is behind the formation of the pseudogap at the Fermi level. The contours of the valence charge densities show combinations of metallic and covalent bonds. The number of bonding electrons per atom n b , the electronic specific heat coefficient g , and the electron-phonon coupling constant l , are determined. The obtained values of the magnetic moments and polarization coincide with the reported values for both D0 22 and L1 2 structures. Moreover, the optical properties, including the dielectric functions, extinction coefficient K( u ), reflec- tivity coefficient R( u ) and energy loss function L( u ) are studied in the range of 0e14 eV.

Résumé: In this work, the first-principles computational study on the structural, elastic, electronic and optical properties of Y x Ga 1−x As as a function of yttrium concentration (x) is presented. The computations are performed using the full- potential linearized augmented plane wave plus local orbital method designed within density functional theory. Firstly, we performed our calculations on the most stable phases, NaCl and zinc blende, then their transition pressure for each concentration is determined and analysed. Our computed results for the zero yttrium concentration are found consistent with the available experimental measurements as well as with theoretical predictions. Moreover, the dependencies of these parameters upon yttrium concentration (x) were found to be non-linear. We also report computed results on electronic-band structure, electronic energy band gap results and density of states. A systematic study on optical properties to analyse its optoelectronic character and elastic properties is presented.

Résumé: The structural, electronic, and thermal properties of the BeSiAs 2 and MgSiAs 2 chalcopyrite compounds have been investigated using the full-potential linearized augmented plane wave (FP-LAPW) method. The exchange-correlation part of the potential is treated within the Wu and Cohen generalized gradient approximation (WC-GGA). Moreover, Tran and Blaha modified Becke-Johnson (TB-mBJ) scheme is also applied for electronic properties. Our calculated ground-state properties, including the lattice constants, internal parameters, and the bulk moduli are found in reasonable agreement with the available data. The computed band structures reveal a direct bandgap semiconducting nature of both compounds. The thermodynamic properties are also predicted through the quasi-harmonic Debye model. We also analyze the effect of pressure on the structural phase transition and the electronic properties, besides investi- gating the effect of temperature and pressure on the bulk modulus, heat capacities, and the Debye temperatures of the title materials.

Résumé: The aim of this study is to calculate the structural, electronic and optical properties of M 1-x Pr x F 2+x (M = Ba, Ca, x = 0.25). The calculations are performed by the spin-polarized density functional theory (DFT) combined with Hubbard U correction method. The band gaps of Ba 0.75 Pr 0.25 F 2.25 and Ca 0.75 Pr 0.25 F 2.25 are calculated and compared to the binary fluorides BaF 2 and CaF 2 . It is found that the band gaps of the strongly substituted compounds in Praseodymium are smaller than those of the binary materials. The values obtained are 3.21, 2.77, 6.95, 7.14 eV for Ba 0.75 Pr 0.25 F 2.25 , Ca 0.75 Pr 0.25 F 2.25, BaF 2 and CaF 2 respectively. The comparison between Ba 0.75 Pr 0.25 F 2.25 and Ca 0.75 Pr 0.25 F 2.25 is discussed by computing the optical pa­ rameters using LSDA and LSDA + U approximations, such as dielectric function, refractive index, reflectivity, absorption, extinction coefficient and energy loss function over a wide range of energy, 0.0–40.0eV. These results would provide a theoretical reference for fundamental science as well as technological application of these compounds. The electronic and optical properties predicted in this work for M 1-x Pr x F 2+x (M = Ba, Ca, x = 0.25) may serve as reference for the other experimental and theoretical studies.

Résumé: In this study, density functional theory (DFT) calculations were performed to investigate the structural stability of different crystallographic phases, the pressure-induced phase transition, the electronic and thermal properties of BAs and BP compounds. The zinc blende (B3), wurtzite (B4), NaCl (B1), CsCl (B2), NiAs (B8), crystal structures are considered. The Perdew-Wang local density approximation (LDA), the Perdew-Burke-Ernzerhof generalized gradient approximation (PBE-GGA) and the newly form (WC) of the generalized gradient approximation (GGA) that was proposed by Wu and Cohen are used to treat the exchange-correlation terms. Moreover, the modified Becke-Johnson (mBJ) scheme is also applied for the band structure calculations. At zero pressure, our findings show that the zinc blende structure is the most stable phase adopted by these compounds. The transition pressure between the various phases is calculated. The band structure calculations reveal a metallic behaviour in NaCl, CsCl and NiAs structures whereas for the other structures, a semiconducting behaviour is observed. The quasi-harmonic Debye model has been used to explore the temperature and pressure effects on the thermal properties for both the compounds

Résumé: In this work, we have investigated the structural, electronic and thermodynamic properties of GaP 1−x Sb x and AlP 1−x Sb x ternary alloys for a number of ordered structures and compositions in a series of first- principles calculations within the density functional theory, using full potential-linearised augmented plane-wave (FP-LAPW) method, as implemented in the WIEN2k code. The exchange-correlation effect was treated within the generalised gradient approximation (GGA) in the form of GGA-PBEsol to optimise the structure and to compute the ground-state properties. In addition to the GGA, the modified Becke–Johnson (mBJ) potential coupled with the spin-orbit interaction (SOI) was also applied to obtain reliable results for the electronic properties. Our investigation on the effect of composition on lattice constant, bulk modulus and band gap showed almost nonlinear dependence on the composition. The GaP 1−x Sb x and AlP 1−x Sb x alloys are found to be semiconductors with a positive energy gap for the whole concentration range. The spin-orbit splitting  SO was found to increase with Sb composition with a marginal bowing parameter. Besides, a regular-solution model was used to investigate the thermodynamic stability of the alloys which mainly indicates a phase miscibility gap. In addition, the quasiharmonic Debye model was applied to analyse the effect of temperature and pressure on the Debye temperature and heat capacity.

Résumé: In this study, first-principles numerical computations for zinc-blende ternary alloys (In 1−x Al x Sb) are performed concerning elastic, structural, electronic, thermal, and optical properties. This study is carried out using the “full-potential linearized augmented-plane- wave plus local-orbital, (FP-L(APW + lo))” approach framed within “density functional theory" and realized in the WIEN2k computational package. From our computational work, performed at the level of generalized gradient approximation suggested by Wu and Cohen (GGA-WC) for the exchange–correlation functional, we see that our obtained results for the structural parameters of the title alloys ( ­ In 1−x Al x Sb) are increasing with increasing con- centration x, and by and large, follow the Vegard’s law. To predict reliable electronic and optical properties "Tran–Blaha modified Becke–Johnson (mBJ)" potential approach was employed. We note, except at x = 1 and x = 0.75, electronic band gaps are of direct nature for evaluated concentrations of the title alloys. In addition, noticeable variation is noted in the optical parameters with x concentration. For analyzing the thermal character of the title alloys, the "quasi-harmonic Debye model" scheme is used. Comparison of obtained results with experimental and predicted ones is found in good agreement where available. Hence our computational study of the title alloys endorses the reliability of our investigations and might offer a valuable platform for future predictions and experimental work as well as suggest that title material is the best candidate for optoelectronics. The optical quantities obtained using mBJ show low energy loss and reflectivity and high absorption capability in the infrared and visible regions for ­In 1−x Al x Sb, making these materials potential candidates in solar cell applications.