Cohen Generalized Gradient Approximation Research Articles

Structural, band profiles and optical reflectivity studies of ALi2B (A = Cu, Ag; B = Ge, Sn, Pb) compounds

Abstract The subject of given project is to highlight the basic elastic, electronic and optical reflectivity of ALi2B (A = Cu, Ag; B = Ge, Sn, Pb). For the calculation of these properties, we used the full potential linearized augmented plane wave (FP-LAPW) procedures carry through Wien2k package. Specifically, the Perdew, Burke and Ernzerhof’s generalized gradient approximation (PBE-GGA) and Wu and Cohen generalized gradient approximation (WC-GGA) have been used. The obtained results fit well with existing experimental data. Different elastic parameters, such as constant of elasticity, elastic moduli, Poisson’s ratio, anisotropy factor and Cauchy pressure, are calculated for the first time for the compounds. The elastic properties clearly summarized the compound’s elastically stability and brittleness in both zinc blend phase. The band structure results for ALi2B shows that the compounds are metallic having overlapping bands across the electron chemical potential. The valance band highest energy state is composed from combination of Cu-d and Sn-p state, disclosed through these compound’s total (DOS) plots, whereas the conduction band primarily constitution is from Li-p, Sn-s Cu-s and Sn-p states. The intraband transitions play vital rule in the description of the optical reflectivity of the ALi2B compounds.

Structural, Electronic and Magnetic Properties of CaSe Doped with 3d (V, Cr and Mn)

We report first-principles investigation on structural, electronic and magnetic properties of 3d transition metal element-doped rock-salt calcium selenide Ca[Formula: see text]TMxSe (TM = V, Cr and Mn) at concentrations [Formula: see text] = 0.0625, 0.125 and 0.25. We performed the calculations in the framework of the density functional theory (DFT) using the full-potential linearized augmented plane waves plus local orbitals (FP-LAPW+lo) method within the Wu–Cohen generalized gradient approximation (WC-GGA) for the structural optimization and the Tran–Blaha modified Becke–Johnson (TBmBJ) potential for the electronic and the magnetic properties. The computed spin-polarized band structures and densities of states show that Ca[Formula: see text]CrxSe compounds at all studied concentrations are half-metallic ferromagnets with a complete spin polarization of 100% at Fermi-level while the Ca[Formula: see text]VxSe and Ca[Formula: see text]MnxSe are ferromagnetic semiconductors. The total magnetic moments for Ca[Formula: see text]VxSe, Ca[Formula: see text]CrxSe, and Ca[Formula: see text]MnxSe show the integer values of 3[Formula: see text][Formula: see text], 4[Formula: see text][Formula: see text], and 5[Formula: see text][Formula: see text], respectively, with a major contribution of transition metal elements (TM) in the total magnetization. Also, we reported the calculated exchange constants [Formula: see text] and [Formula: see text] and the band edge spin splitting of the valence ([Formula: see text]) and conduction ([Formula: see text]) bands. The ferromagnetism of these compounds is due to the super-exchange and the double-exchange mechanisms in addition to the strong p–d exchange interaction. Therefore, the predicted results indicate that the diluted Ca[Formula: see text]TMxSe (TM = V, Cr, Mn) compounds are suitable candidates for a possible application in the field of spintronic technology.

Study of the chromium doping effect in boron phosphide semiconductors

According to the firs-principles theory-based spin-density functional calculations within the framework of Wu–Cohen generalized gradient approximation (WC-GGA), we examine the structural and electronic properties of ternary alloys of zinc-blende boron phosphide doped with chromium. We compare the materials with aluminum phosphide that exhibits half-metallic properties at various concentrations. The curves of total and partial densities of states and the band structures show that [Formula: see text][Formula: see text]P are purely metallic and can be possible candidates for use in light emitting diodes (LEDs). These compounds are not polarized on spins; the main cause is the nature of chemical bond located between the boron cations and the phosphorus anion, whereas the ternary materials of [Formula: see text][Formula: see text]P all have various uses in spintronic science according to many studies because of their half-metallicity behavior.

Metallic Ferromagnetic Property of Mn-Doped BP Semiconductors

The doping of boron phosphide (BP) with manganese as magnetic impurity at different concentrations provides metallic ferromagnetic materials B[Formula: see text]MnxP at ([Formula: see text], 0.125, 0.0625). Their structural and electronic properties are calculated by the first-principle spin-density functional theory (DFT) within the framework of the Wu–Cohen generalized gradient approximation (WC-GGA). The DMSs BP originated from doping manganese contributed in SP3 hybridization of tetrahedral crystal field caused by the surrounding of four phosphorus anions. These compounds are not half-metallic but exhibit a poorly metallic ferromagnetic nature, the cause is due to the highly covalent chemical bond of BP. The B[Formula: see text]MnxP are metallic ferromagnetic materials and are not to be intended for spintronic industry.

Pressure effect on the structural, electronic, and thermal properties of chalcopyrite compounds MgSiAs2 and BeSiAs2

The structural, electronic, and thermal properties of the BeSiAs2 and MgSiAs2 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 investigating the effect of temperature and pressure on the bulk modulus, heat capacities, and the Debye temperatures of the title materials.

Structural and Electromechanical Properties of Sr-Substituted Barium Titanate (BST) as Potential Material for High Performance Electroacoustic Devices

First-principles density functional calculations have been performed to study the electromechanical properties, i.e., elastic, dielectric, piezoelectric, and coupling factors, as well as the crystal structure for Ba1―xSrxTiO3 (BST) with 0≤ x ≤1 in the paraelectric and ferroelectric crystallographic phases. The equilibrium ground state structural parameters are calculated using the new Wu–Cohen Generalized Gradient Approximation (GGA―WC) in excellent agreement with the experimental data. The lattice stabilities in Ba1―xSrxTiO3 crystals are analysed from the doped formation energy and phonon dispersions. The mechanical quantities, such as the elastic constants (C11, C12, C44, C13, C33 and C66), mechanical moduli (Young modulus Y, Shear modulus G, Compressibility B), Poisson’s ratio and elastic anisotropy are investigated using the GGA―WC and GGA―PBEsol exchange functionals. The mechanical moduli (B, G and Y) are found to increase by increasing Sr content leads to enhance stiffness and hardness of BST systems. We find that both the para- and ferroelectric phases of all considered Ba1―xSrxTiO3 are elastically stable. The 3D surface anisotropy visualizations show that BST is a pure isotropic material at x∼ 0.5. It was found that Debye temperature (ΘD), milting temperature (TM) and acoustic wave velocities increase as the Sr content increases. The ferroelectric Ba0.75Sr0.25TiO3 (BST) exhibited high piezoelectric coefficients [d15 = 121.4 pC/N, d31= -20.5 pC/N, d33 = 89.3 pC/N], and large dielectric tensors [ε11 = 517.2, ε33 = 31.3], compared to pure BaTiO3 [d15 = 74.2 pC/N, d31= -14.1 pC/N, d33 = 65.0 pC/N; ε11 = 334.7, ε33 = 22.6]. Enhancement in electromechanical coupling factor and bulk acoustic velocity of ferroelectric BST is achieved when the Sr content is added. Ba1―xSrxTiO3 (BST) are extremely interest candidates to be used for the development of high performance electroacoustic devices such as acoustic sensors and resonators.

Phase stability, mechanical, electronic, magnetic and optical properties of tetragonal and cubic M3V (M: Pd, Pt) structures

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 M3V (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(EF) show that the D022 structure is more stable than D023 and L12. 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 nb, the electronic specific heat coefficient γ, and the electron-phonon coupling constant λ, are determined. The obtained values of the magnetic moments and polarization coincide with the reported values for both D022 and L12 structures. Moreover, the optical properties, including the dielectric functions, extinction coefficient K(ω), reflectivity coefficient R(ω) and energy loss function L(ω) are studied in the range of 0–14 eV.

Theoretical Investigation of the Electronic Structure and Magnetic Properties in Ferromagnetic Rock-Salt and Zinc Blende Structures of 3d (V)-Doped MgS

In this work, we studied the properties of vanadium doped binary MgS compound Mg1−xVxS (x = 0.125, 0.25, 0.50 and 0.75) in both ferromagnetic rock-salt and zinc-blende structures. The studied properties are structural, electronic and magnetic. The objective of this study is to explore the new dilute magnetic semiconductor systems. We have used two approximations to simulate these properties: Wu–Cohen generalized gradient approximation for structural properties, and the modified Becke–Johnson potential combined with the local density approximation for electronic and magnetic properties. The general context in which the calculations are done is based on the formalism of the spin-polarized density functional theory and the full-potential linear-augmented plane wave method. Among the various compounds studied, we have identified a ferromagnetic semiconducting behavior in the rock-salt structure. In the zinc-blende structure, we have one metallic candidate consisting of 75% V-doping of the Mg-sublattice, and all other compounds have a half-metallic ferromagnetic behavior. We conclude that the Mg1−xVxS compounds, for x = 0.125, 0.25 and 0.50, in the zinc-blende structure are a diluted magnetic semi-conductors materials. To see the effects of the exchange splitting process, the exchange constants N0α and N0β are calculated. For each concentration x, we have found the values of the total magnetic moment equal to 3 μβ excepted for the case of Mg0.25 V0.75S compound in the zinc-blende structure. The value of the total magnetic moment is due principally to V magnetic atom and to other both nonmagnetic atoms Mg and S, which show small local magnetic moments localized on their sites. The presence of ferromagnetic order in this type of compound can be explained by the p-d hybridization phenomena.

Ab-initio prediction of structural, electronic and magnetic properties of Hexafluoromanganete(IV) complexes

In this work, detailed electronic structure calculations of alkali metal fluorides A2MnF6 (A = K, Rb, Cs) have been performed using ab-initio calculating techniques based on density functional theory (DFT). We applied different exchange correlation functionals, namely Wu–Cohen generalized gradient approximation (WC-GGA), modified Becke Johnson potential (mBJ) and GGA plus Hubbard U method in order to treat the exchange correlation energy. The calculated lattice constants are found in excellent agreement with earlier experimental results. The electronic band structure and density of states show that Cs2MnF6 is half metallic, exhibiting semiconductivity in spin up direction and metallic behavior in spin down direction. The compounds, K2MnF6 and Rb2MnF6, are predicted as wide bandgap materials. The DFT + U method gives quite accurate results of the electronic bandgap as compared with other approximations. The states Mn-3d and F-2p contribute largely to the conduction and valence energy bands. Additionally, magnetic calculations reveal strong ferromagnetic nature of these compounds. The half-metallic nature along with ferromagnetism make Cs2MnF6 a promising candidate for future applications in spintronics. Furthermore, the wide bandgap observed in K2MnF6 and Rb2MnF6 indicate their utility for light-emitting diodes (LEDs) transparent lenses and optical coatings.

Insight into the structural, electronic, elastic and optical properties of the alkali hydride compounds, XH (X = Rb and Cs)

The equilibrium structural parameters, electronic and optical properties of the alkali hydrides RbH and CsH compounds in rock-salt (RS) and cesium chloride (CsCl) structures have been studied using the full-potential linearized augmented plane-wave (FP-LAPW) method. Wu and Cohen generalized gradient approximation (WC-GGA) was used for the exchange-correlation potential to compute the equilibrium structural parameters, such as the lattice constant (a0), the bulk modulus (B) and bulk modulus first order pressure derivative (B'). In addition to the WC-GGA, the modified Becke Johnson (mBJ) scheme has been also used to overcome the underestimation of the band gap energies. RbH and CsH compounds are found to be semiconductors (wide energy-band gap) using the WC-GGA method, while they are insulators using the mBJ-GGA method. Elastic constants, mechanical and thermodynamic properties were obtained by using the IRelast package. RbH and CsH compounds at ambient pressure are mechanically stable in RS and CsCl structures; they satisfy the Born mechanical stability criteria. Elastic constants (Cij), bulk modulus (B), shear modulus (S) and Debye temperatures (θD) of RbH and CsH compounds decrease as the alkali radius increases. The RS structure of these compounds at ambient conditions is mechanically stronger than CsCl structure. RbH and CsH in RS and CsCl structures are suitable as dielectric compounds. The wide direct energy band gap for these compounds make them promising compounds for optoelectronic UV device applications. Both RbH and CsH have a wide absorption region, on the other hand RbH absorption is very huge compared to the CsH absorption, RbH is an excellent absorbent material, maximum absorption regions are located in the middle ultraviolet (MUV) region and far ultraviolet (FUV) region. The absorption coefficient α (w), imaginary part of the dielectric constant ε2(w) and the extinction coefficient k(w) vary in the same way. The present calculated results are in good agreement with the experimental data, indicating the high accuracy of the performed calculations and reliability of the obtained results.

Optoelectronic properties of the new quaternary chalcogenides Zn2CuInTe4 and Cd2CuInTe4: Ab-initio study

In order to exploit the fundamental properties of the new tellurides quaternary diamond-like structure Zn2CuInTe4 and Cd2CuInTe4, first principles investigation in the framework of the Full-Potential LAPW scheme have been carried out for that purpose. We used the Wu and Cohen generalized gradient approximation (GGA-WC) to calculate the optimized structure that corresponds to the global minima of the energy. Enthalpy of formation shows that the most stable structures are the relaxed ones. The EV-GGA and the TB-mBJ approximations were also used for electronic and optical properties. The equilibrium electronic parameters found are in good agreement with the previous results. The real and thecient, the opt imaginary parts of the dielectric function, the refractive index, the extinction coeffiical conductivity, the absorption coefficient, the loss function and the reflectivity are reviewed in the large spectral range of photon energy. The present study demonstrates a variety of novel electronic and optical properties, which make these compounds highly promising for optoelectronic materials.

Highly desirable semiconducting materials for mid-IR optoelectronics: Dilute bismide InAs1−xBix alloys

We have performed a self-consistent full-potential linearized augmented plane wave (FP-LAPW) method within density functional theory (DFT) to investigate the structural, electronic and optical properties of the dilute bismide InAs1−xBix alloys (0≤x≤0.125) for mid-IR optoelectronics application. The ground state properties including the lattice constant a0 and bulk modulus B0 are obtained by using Wu–Cohen generalized gradient approximation (WC-GGA), show agreement with experimental data. The calculated band gap energy (Eg) using Tran–Blaha-modified Becke–Johnson scheme (TB-mBJ) with spin-orbit coupling, show close agreement to experimental Eg. InAs1−xBix alloys exhibits large band gap reduction for small Bi compositions (∼380meV for x=0.125) covering the mid- and far-IR (∼2.6–14μm) wavelengths range. The narrow-band gap in InAs1−xBix alloys can be attributed to the both resonant interaction of Bi-p states with the valence band maximum (VBM) and the hybridization (anticrossing) of the unoccupied s/p orbitals of In/As/Bi atoms with the host conduction band (CB). The dielectric functions and optical parametric quantities such as refractive index, extinction coefficient, absorption coefficient, reflectivity and energy loss function are determined for radiation range 0–10eV in comparison with available experimental data. The critical-point (CP) energies have been identified from the computed electronic band structure in agreement with measured data. This makes InAs1−xBix potential materials for fabrication advanced optoelectronic devices as photodetectors and laser diodes operating in the mid-IR wavelengths region.

First-principles study of the double perovskites Sr2XOsO6 (X = Li, Na, Ca) for spintronics applications

We investigated double perovskite compounds of the form Sr 2 XOsO 6 (X = Li, Na, Ca) using the full-potential linearized augmented plane wave (FP-LAPW) method. For the exchange-correlation energy, Wu and Cohen generalized gradient approximation (WC-GGA), Perdew, Burke and Ernzerhof GGA (PBE-GGA), Engel and Vosko GGA (EV-GGA), and GGA plus Hubbard U-parameter (GGA + U) were used. The calculated structural parameters are in good agreement with the existing experimental results. Calculation of different elastic constants and elastic moduli reveals that these compounds are elastically stable and possess ductile nature. The GGA + U approach yields quite accurate results of the bandgap as compared with the simple GGA schemes. The density of states plot shows that Sr-4d, Os-5d and O-2p states predominantly contribute to the conduction and valence bands. Further, our results regarding to the magnetic properties of these compounds reveal their ferromagnetic nature. In addition, these compounds seem to possess half-metallic properties, making them useful candidates for applications in spintronics devices.

Electronic structure and magnetic properties of Zn1−xTMxTe (TM = Fe, Co, Ni) for 0 ≤ x ≤ 1 alloys

In this study, we employed Wu–Cohen generalized gradient approximation (WC-GGA) to calculate the structural stability, whereas the modified Becke and Johnson local-density approximation (mBJLDA) functional has been used to determine the electronic and magnetic properties of [Formula: see text] [Formula: see text] alloys in the [Formula: see text] range 0–1. Structural optimization in paramagnetic (PM), ferromagnetic (FM) and anti-ferromagnetic (AFM) orders has been done to check the state stability of the doped alloys and then verified with the calculated values of enthalpy of formation [Formula: see text]. The erections of enthalpies were negative which gave the evidence of structural stability in FM phase for all three alloys. Our calculated values of equilibrium lattice constants decreased by increasing the TM concentration, in [Formula: see text] [Formula: see text] alloys. We found ferromagnetism caused by the spin polarization of electron in TM-[Formula: see text] states in the studied alloys by analyzing the calculated band structure (BS), density of state (DOS) and magnetic moments. The calculated ferromagnetism was also explained from the Zener model. Due to the tetrahedral crystal field, the [Formula: see text]-state of TM splits into double [Formula: see text] and triple degenerate [Formula: see text] states and our calculated results show the strong pd interaction is only due to [Formula: see text]. Furthermore, we predict exchange splitting energies [Formula: see text] and [Formula: see text] and exchange constants [Formula: see text] and [Formula: see text]. Their calculated values are consistent with typical magneto-optical experiment. The magnetic moments of TM ions were reduced by increasing TM concentration in [Formula: see text] [Formula: see text] alloys, while trivial local magnetic moments at Zn and Te sites were also found.

Full-potential calculations of structural and optoelectronic properties of cubic indium gallium arsenide semiconductor alloys

In this work, the first-principle calculations have been performed to predict the structural, electronic and optical properties of cubic InxGa1−xAs for 0≤x≤1, using 16-atom within the Full Potential Linearized Augmented Plane Wave (FP-LAPW) method based on Density Functional Theory (DFT) as implemented in WIEN2k computational code. The Local Density Approximation (LDA) and Wu–Cohen Generalized Gradient Approximation (WC–GGA) were employed as the exchange–correlation term to calculate the structural and electronic properties. Moreover, the Engel–Vosko GGA (EV-GGA) and the recently modified semi–local Becke–Johnson (mBJ) functional were also used to compute the electronic and optical properties in order to get some better degree of precision. The real and the imaginary parts of the dielectric function, refractive index, extinction coefficient, reflectivity, absorption coefficient and optical conductivity were calculated to discuss the linear optical properties of InxGa1−xAs alloys. The achieved results show a great potential utilization in optoelectronic devices especially in infrared applications.

The study of electronic, elastic, magnetic and optical response of Zn1-xTixY (Y = S, Se) through mBJ potential

To explore the structural, electronic, magnetic and optical properties of Zn1-xTixY (Y=S, Se) alloys, in the composition range 0 ≤ x ≤ 1, we have applied full-potential linearized augmented plane wave plus local orbital (FP-LAPW + lo) scheme, which is based on the density functional theory (DFT). Structural optimizations have been done in ferromagnetic (FM) and antiferromagnetic (AFM) phase by using Wu–Cohen generalized gradient approximation (WC-GGA), whereas recently developed modified Becke and Johnson (mBJ) potential was employed to study electronic and optical properties. The lower value of ground state energy and negative enthalpy of formation confirm stability in the FM phase. Due to the spin polarization of electrons in the Ti-d orbital, origin of half-metallic ferromagnetism has been expressed by the calculated band structures, electronic density of states (DOS) and magnetic moments. We also have calculated the exchange splitting energy Δx (d), crystal field energy (ΔEcrystal = Et2g−Eeg) and exchange constants (N0α and N0β). The negative value of exchange constant (N0β) and large splitting of 3d-states of Ti show that the down spin potential is more effective than up spin. Finally, the results of optical parameters such as complex dielectric constant ε (ω), refractive index n (ω), normal incident reflectivity R (ω), absorption coefficient ɑ (ω), optical conductivity σ (ω) and optical loss factor L (ω) are discussed in the energy range 0–14 eV. Moreover, we have verified the Penn's model by showing the inverse relation between the static dielectric constant and the optical band gap. The direct relation between static dielectric constant and static refractive index has been observed by increasing the composition of Ti. The calculated parameters provide valuable theoretical information for optical and spintronics device applications.

Study of Half-Metallic Ferromagnetism in Be0.75Ti0.25Y (Y = S, Se, and Te) Using Ab Initio Calculations: Potential Candidate for Spintronic Devices

The structural, elastic, electronic, and magnetic properties of Be0.75Ti0.25Y (Y = S, Se, and Te) have been investigated to understand their potential applications in spintonic devices. Crystals of BeS, BeSe, and BeTe, individually doped with Ti with a dopant concentration of x = 0.25, have been evaluated by using full-potential linearized augmented plane-wave plus local orbital method within the framework of density functional theory. We employed the Wu–Cohen generalized gradient approximation for optimizing the crystal structure and evaluating elastic properties. In order improve bandgap values and optical parameters, the modified Becke and Johnson (mBJ) potential has been employed. The theoretical investigation of band structure and density of states confirms the half-metallic ferromagnetic nature of these compounds. The elastic constants are calculated by the charpin method which shows that the compounds under consideration are brittle and anisotropic. Moreover, it is noted that tetrahedral crystal field splits the 3d state of Ti into triple degenerate t2g and double degenerate eg states. The exchange splitting energies Δx(d) and Δx(pd) and exchange constants (N0α) and (N0β) are predicted from triple degenerate t2g states, and negative values of N0β justify that the nature of effective potential is more attractive in spin down case rather than that in the spin up case. We also find the crystal field splitting (ΔEcrystal = Et2g−Eeg) energy and reduction of the local magnetic moment of Ti from its free space charge value and creation of small local magnetic moments on the non-magnetic Be, S, Se, and Te sites by p–d hybridization.

First-principles investigation of structural, elastic, electronic and magnetic properties of Be0.75Co0.25Y (Y[dbnd]S, Se and Te) compounds

We have theoretically investigated the structural, elastic, electronic and magnetic properties of Be0.75Co0.25Y (YS, Se and Te) alloys, in their zinc-blend phase. This study is carried out by using the full-potential augmented plane wave plus local orbitals method within the density functional theory. Foe computing the exchange-correlation potential, the Wu and Cohen generalized gradient approximation is employed to calculate structural and elastic properties whereas the modified Becke and Johnson potential local density approximation is utilized to examine electronic and magnetic properties. By minimizing the total energy in paramagnetic (PM) and ferromagnetic (FM) phases, it is found the studied compounds are stable in FM structure. The mechanical behavior of the studied compounds is reported with the calculation of shear modulus, Young's modulus, and Poisson's ratio provides. Such mechanical aspects might be useful for the experimentalists to study the mechanical properties upon alloying BeY compounds with Co. We also compute electronic structures, density of states (total and partial), pd-exchange splitting and magnetic moments. Moreover, bond nature is studied by estimating the spin polarized charge densities of Be0.75Co0.25Y (YS, Se and Te).

First-principle calculations of the structural, electronic, thermodynamic and thermal properties of ZnS x Se1−x ternary alloys

First-principle calculations were performed to study the structural, electronic, thermodynamic and thermal properties of ZnS x Se1−x ternary alloys using the full potential-linearized augmented plane wave method (FP-LAPW) within the density functional theory (DFT). In this approach the Wu–Cohen generalized gradient approximation (WC-GGA) and Perdew–Wang local density approximation (LDA) were used for the exchange–correlation potential. For band structure calculations, in addition to WC-GGA approximation, both Engel–Vosko (EV-GGA) generalized gradient approximation and recently proposed modified Becke–Johnson (mBJ) potential approximation have been used. Our investigation on the effect of composition on lattice constant, bulk modulus and band gap for ternary alloys shows a linear dependence on alloy composition with a small deviation. The microscopic origins of the gap bowing were explained using the approach of Zunger and co-workers. Besides, a regular-solution model was used to investigate the thermodynamic stability of the alloys which mainly indicates a phase miscibility gap. Finally, the quasi-harmonic Debye model was applied to see how the thermal properties vary with temperature at different pressures.

Phase stability and electronic properties of silver halides

In this work, we study the phase stability and electronic properties of silver halides ( AgBr, AgCl and AgI) using the full-potential linearized augmented plane wave method within the density functional theory. In this approach, the Wu–Cohen generalized gradient approximation was used for the exchange–correlation potential. Moreover, the modified Becke–Johnson approximation was also used for band-structure calculations. Various structural phase transitions were considered here in order to confirm the most stable structure and to predict the phase transition under hydrostatic pressure. In addition, we have studied the band structures of the stable phases of these compounds which reveal that the three compounds exhibit semiconducting behavior. The results obtained are compared with other calculations and experimental measurements.