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In this work, we will investigate structural, electronic, magnetic, and thermodynamic properties using density functional theory (DFT) and the quasi-harmonic Debye model. We consider ferromagnetic (FM) and non-magnetic (NM) states for L2₁ and Hg₂CuTi-type crystal structures. The best stability is obtained for ferromagnetic Rh₂MnGa in a Cu₂MnAl structure with a lattice parameter of 6.07 Å and a total magnetic moment of 4.11${\mu }_B$. The compressive strain range from $-6$% to $+4$% tensile strain maintains the ferromagnetic nature and enhances the magnetic moment up to 4.39${\mu }_B$. The formation energy confirms the inherent stability of Rh₂MnGa. Other important thermodynamic parameters such as the expansion coefficient ($\alpha$), heat capacity ($C_V$), Debye temperature (${\theta }_D$) and Grüneisen constant ($\gamma$) are also estimated in this work.

First principles investigation of PbTiO₃ in bulk and layer phases has been performed using full potential-linear augmented plane wave method (FP-LAPW) implemented in WIEN2K code, based on the density functional theory (DFT) within the generalized gradient approximation (GGA) to explore the structural, electronic, thermoelectric and optical properties of PbTiO₃. Total energy calculations, optimized structure, band structure, density-of-states (DoS), optical, and thermoelectric properties are computed and analyzed. The change in structural and electronic phases are observed. The optical properties of the compound can be studied by evaluating from the optical spectra and the changes in the properties such as complex dielectric function, absorption, energy loss function, refractive index and refractivity are studied. The thermoelectric properties are analyzed from Seebeck coefficient, power factor and thermoelectric figure of merit. The superior phase of PbTiO₃ is analyzed from the observation of all the above-mentioned properties for optoelectronic applications.

For quite a long time, the scientific community has been searching for a material that surpasses the existing material systems in terms of energy conversion efficiency for photovoltaic applications. In this study, the optoelectronic properties of pure and Al-doped boron arsenide B${{}_{1-}}_x$Al${}_x$As $(x=0,0.125\mathrm{\text{and}}0.25)$ in the zinc blende (ZB) structure were systematically examined using the density functional theory (DFT) and the Modified Becke–Johnson (TB-mBJ) exchange correlation (XC) potential. The Perdew–Burke–Ernzerhof generalized gradient approximation (PBE) functional was used for structural optimization. After considering the ground state lattice constant of 4.82Å then calculating the bandgap energy of pure BAs, which are consistent with experimental and theoretical findings, we estimated the basic electronic and optical characteristics of Al-doped boron arsenide, including band structures, electronic density of state, dielectric function, refractive index, extinction coefficient, absorption and optical conductivity. The unusual and interesting optoelectronic features of the investigated compounds revealed in this work offer substantial promise for improving the energy conversion efficiency of solar cells.

Adsorption of hydrogen atoms on pure and modified graphene layers was studied by density functional theory (DFT). Modifications were made to the graphene layers by adding M adatom (M $=$ O or F). The relaxed structures, energetic, electronic and magnetic properties of the M-graphene, H-graphene and M-graphene-NH layers were studied theoretically using the full-potential linearized augmented plane wave (FP-LAPW) within the generalized gradient approximation (GGA). The results showed that the presence of O or F as adatom on graphene allowed the stability of multi-H atom adsorption with a large and positive adsorption energy. A bandgap opening was observed for O-graphene-3H and O-graphene-4H sheets. Also, O-graphene, O-graphene-H and F-graphene-NH were found to have metallic behavior. O-graphene-3H sheet was found to have a half-metallic ferromagnetic behavior since its total magnetic moments is equal to an integer. In addition, the band structure shows that O-graphene-3H sheet is a semiconductor. Useful optical applications are predicted for M-graphene-NH sheet due to the absorption and reflectivity results.

The actinide compounds exhibit a variety of unusual ground states. These states are dominated by the strong electron-electron correlations that are not included in normal density-functional electronic band-structure calculation with the local density approximation. These correlations are taken into account in the local density approximation +U (LDA+U) method.

We have calculated the Coulomb repulsion term U for uranium in USn₃ compound, and investigated the total and partial DOS for USn₃ using LDA+U method. The LDA+U results for USn₃ have been compared with similar results from a ThSn₃ model calculation through which the number of 5f electrons outside the U muffin-tin sphere in USn₃ has been deduced. We have also calculated the electric field gradient (EFG), which may be regarded as a measure of the asymmetry in charge distribution, at the Sn site in USn₃ in LDA, LDA+SO and LDA+SO+U methods, and have shown that the Coulomb repulsion term does not introduce any considerable effect on the electric field gradient at the Sn site.

The ground state properties and the structural phase transformation of tin dioxide (SnO₂) have been investigated using first principle full potential-linearized augmented plane wave (FP-LAPW) method within density functional theory (DFT). We used local density approximation (LDA) and the generalized gradient approximation (GGA), which are based on exchange-correlation energy optimization, to optimize the internal parameters by relaxing the atomic positions in the force directions and to calculate the total energy. For band structure calculations, we utilized both the Engel-Vosko's generalized gradient approximation (EVGGA), which optimizes the exchange-correlation potential, and also GGA. From the obtained band structures, the electron (hole) valance and conduction effective masses are deduced. For compressed volumes SnO₂ is shown to undergo two structural phase transitions with increasing pressure from the rutile- to the CaCl₂-type phase at 12.4 GPa and to a cubic phase, space group at 22.1 GPa. The calculated total energy allowed us to investigate several structural properties, in particular, the equilibrium lattice constants, bulk modulus, cohesive energy, interatomic distances and the angles between different atomic bonds. In addition, we discuss the bonding parameter in term of charge density, which show the localization of charge around the anion side.

The structural optimization was followed by the calculation of electronic structure and magnetic properties on Co₂CrAl and Co₂CrGa. The structure optimization was based on generalized gradient approximation (GGA). The calculation of electronic structure was based on full potential linear augmented plane wave (FPLAPW) method within local spin density approximation (LSDA). We studied the electronic structure and magnetic properties. Results of density of states (DOS) and band structures shows that Co₂CrAl and Co₂CrGa are half-metallic ferromagnets (HMFS). The calculated magnetic moments of Co₂CrAl and Co₂CrGa are 2.915 and 3.075 μ_B, respectively. We have calculated the onsite d–d coulomb and exchange interaction (U) For 3d elements like Co and Cr. The strongly localized d states were treated with LSDA+U method.

The structural, electronic thermodynamic and thermal properties of Ba_xSr_1-xTe ternary mixed crystals have been studied using the ab initio full-potential linearized augmented plane wave (FP-LAPW) method within density functional theory (DFT). In this approach, the Perdew–Burke–Ernzerhof-generalized gradient approximation (PBE-GGA) was used for the exchange-correlation potential. Moreover, the recently proposed modified Becke Johnson (mBJ) potential approximation, which successfully corrects the band-gap problem was also used for band structure calculations. The ground-state properties are determined for the cubic bulk materials BaTe, SrTe and their mixed crystals at various concentrations (x = 0.25, 0.5 and 0.75). The effect of composition on lattice constant, bulk modulus and band gap was analyzed. Deviation of the lattice constant from Vegard's law and the bulk modulus from linear concentration dependence (LCD) were observed for the ternary Ba_xSr_1-xTe alloys. The microscopic origins of the gap bowing were explained by using the approach of Zunger and co-workers. 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. It was shown that these alloys are stable at high temperature. Thermal effects on some macroscopic properties of Ba_xSr_1-xTe alloys were investigated using the quasi-harmonic Debye model, in which the phononic effects are considered.

First principle calculations on cesium chloride (CsCl) compound have been performed using state of the art full potential linearized augmented plane wave (FP-LAPW) method. Calculated structural parameters are found in excellent agreement to the experimental results. Band gap of the compound decreases with the increase of pressure. At 507GPa, electronic nature of the compound changed from the insulating to metallic. Changes are reported in the optical properties like real and imaginary parts of dielectric function, optical conductivity and reflectivity of CsCl on application of high pressure.

In this paper, we report a density functional study of the structural, electronic and pressure-induced solid–solid phase transitions of SrTiO₃. These first-principles calculations have been performed using the full potential linearized augmented plane wave method (FP-LAPW) within the generalized gradient approximation (GGA) developed by Perdew–Burke–Ernzerhor for solids (PBEsol). The calculated structural parameters like the lattice parameters, the bulk modulus B and their pressure derivative B′ are used to analyze the relative stability and phase transitions under pressure of SrTiO₃. Calculations were done for the cubic (Pm-3m), tetragonal (I4/mcm, P4/mbm, P4mm) and orthorhombic (Cmcm, Pnma) structures where we found that the tetragonal I4/mcm phase is the most stable structure compared to the other structures at T = 0 K and P = 0 GPa. For the electronic properties calculations, the exchange and correlation effects were treated by the Tran–Blaha modified Becke–Johnson (TB-mBJ) potential to prevent the shortcoming of the underestimation of the energy gaps in both LDA and GGA approximations. The obtained results are compared to available experimental data and to other theoretical calculations.

Optical properties of Zn_1-xMg_xS, Zn_1-xMg_xSe and Zn_1-xMg_x Te(0 ≤ x ≤ 1) ternary semiconductor alloys are calculated using the full potential linearized augmented plane wave within the density functional theory. The exchange correlation potential is treated by the generalized gradient approximation (GGA) within Perdew et al. scheme. The real and imaginary parts of the dielectric function ε(ω), the refractive index n(ω), the extinction coefficient k(ω), the optical absorption coefficient α(ω), the reflectivity R(ω) and the electron energy loss function (EELS) are calculated within random phase approximation (RPA). Our results are compared with the previous theoretical calculations and available experimental data. Moreover, the interband transitions responsible for the structures seen in the spectra are specified. It is shown that, the chalcogen p states as initial and Zn4s, Mg3s, chalcogen d states as final states perform the major role in optical transitions.

The phase stability and electronic properties in Al₃Ta compound are studied using the FP-LAPW method. In this approach, the generalized gradient approximation (GGA) is used for the exchange-correlation potential calculation. The total energy calculations show that the D0₂₂ structure is more stable than that of D0₂₃ and L1₂. The densities of states exhibit a pseudo gap near the Fermi level for all considered structures. By analyzing the electronic charge density we find a build-up of electrons in the interstitial region, and the bonds are directed from the Ta atoms to the Al atoms, which is the characteristic of covalent bonding. The temperature and pressure effects on the structural parameters, Debye temperature, Grüneisen parameter, heat capacities (C_v, C_p) and thermal expansion are predicted through the quasi-harmonic Debye model.

We carried out ab initio calculations of structural, electronic and optical properties of Indium nitride (InN) compound in both zinc blende and wurtzite phases, using the full-potential linearized augmented plane wave method (FP-LAPW), within the framework of density functional theory (DFT). For the exchange and correlation potential, local density approximation (LDA) and generalized gradient approximation (GGA) were used. Moreover, the alternative form of GGA proposed by Engel and Vosko (EV-GGA) and modified Becke–Johnson schemes (mBJ) were also applied for band structure calculations. Ground state properties such as lattice parameter, bulk modulus and its pressure derivative are calculated. Results obtained for band structure of these compounds have been compared with experimental results as well as other first principle computations. Our results show good agreement with the available data. The calculated band structure shows a direct band gap Γ → Γ. In the optical properties section, several optical quantities are investigated; in particular we have deduced the interband transitions from the imaginary part of the dielectric function.

This study combines the use of the full potential linear-augmented plane wave method (FP-LAPW) within the framework of the density functional theory (DFT) and the optical matrix approach for modeling the multilayer assembly. A new class of heterostructures with sufficient number of alternating layers of rutile-TiO₂ (as a high index material) and α-Al₂O₃ (as a low index material) are proposed and their transmittance spectra are investigated. This study shows that the number of alternating layers, and the thickness and arrangement of them should be considered in making a heterostructured filter. The relation between heterostructure parameters and narrow-band-pass peaks of transmittance spectra is investigated. The proposed model seems to be successful in predicting the optical behavior of heterostructures and simulations agree well with the experimental observations. In addition, our model is very flexible and the effect of other parameters such as incident angle and light polarization can be easily investigated.

First-principle calculations are performed using DFT as implemented in Wien2k code to compute the mechanical, electronic, optical and thermoelectric properties of NiYSn (Y = Zr and Hf) alloys. The computed lattice constants, bulk modulus and cohesive energy of these alloys at 0 K and 0 GPa are performed. NiZrSn and NiHfSn are found to be anisotropic and elastically stable. Furthermore, both alloys are confirmed to be thermodynamically stable by the calculated values of the standard enthalpy of formation. The Young’s and shear moduli values show that NiZrSn seems to be stiffer than NiHfSn. The optical properties are performed using the dielectric function. Some beneficial optoelectronic applications are found as exposed in the optical spectra. Moreover, the alloys are classified as good insulators for solar heating. The thermoelectric properties as a function of temperature are computed utilizing BoltzTrap code. The major charge carriers are found to be electrons and the alloys are classified as $p$-type doping alloys.

The structural, electronic, elastic and thermodynamic properties of Curium Monopnictides CmX (X = N, P, As, Sb and Bi) are investigated using first-principles calculations based on the density functional theory (DFT) and full potential linearized augmented plane wave (FP-LAPW) method under ambient condition and high pressure. The exchange-correlation term is treated using two approximations spin-polarized local density approximation (LSDA) and spin-polarized generalized gradient approximation generalized (GGA). The structural parameters such as the equilibrium lattice parameters, bulk modulus and the total energies are calculated in two phases: namely NaCl (B1) and CsCl (B2). The obtained results are compared with the previous theoretical and experimental results. A structural phase transition from B1 phase to B2 phase for Curium pnictides has been obtained. The highest transition pressure is 122 GPa for CmN and the lowest one is 10.0 GPa for CmBi compound. The electronic properties show that these materials exhibit half-metallic behavior in both phases. The magnetic moment is found to be around 7.0 $\mu$B. The mechanical properties of CmX (X = N, P, As, Sb and Bi) are predicted from the calculated elastic constants. Our calculated results are in good agreement with the theoretical results in literature. The effect of pressure and temperature on the thermodynamic properties like the cell volume, bulk modulus and the specific heats C${}_{𝜗}$ and C${}_P$, the entropy ${𝒮}$ and the Grüneisen parameter $\gamma$ have been foreseen at expanded pressure and temperature ranges.

The ab-initio calculations based on the density functional theory (DFT) have been performed to study the structural, mechanical, electronic, thermal and thermodynamic properties of Al₃Sc and Al₃Ti binary compounds and their ternary mixture Al₃(Sc${}_{1-x}$Ti${}_x$) in L1₂ and D0${}_{22}$ structures. The total energy calculations show that the L1₂ structure is the more stable one. The Al₃Sc${}_{0.25}$Ti${}_{0.75}$ undergoes a martensitic transformation and the formation enthalpies and the lattice parameters decrease with increasing concentration x. The elastic constants are determined and the results show that all compounds are mechanically stable and the cubic cells are more easily deformed by shearing than by unidirectional compression. The elastic modulus indicates that the addition of Ti atoms to Al₃Sc improves its ductility. The densities of states (DOSs) calculations show the strong spd hybridization which leads to the formation of a pseudo-gap near the Fermi level in ternary alloys. The densities of states at the Fermi level N(E${}_F$) confirm the phase stability. The quasi-harmonic Debye model is used to predict the thermal properties such as heat capacity, Debye temperature, Grüneisen parameter and thermal expansion coefficient of the considered alloys. The determination of Gibbs free mixing energy at different concentrations has been used to calculate the T–x diagram.

First-principles calculations of the structural, electronic, optical and thermal properties of chalcopyrite CuXTe₂ (X=Al, Ga, In) have been performed within density functional theory using the full-potential linearized augmented plane wave (FP-LAPW) method, by employing for the exchange and correlation potential the approximations WC-GGA and mBJ-GGA. The effect of X cations replacement on the structural, electronic band structure, density of states and optical properties were highlighted and explained. Our results are in good agreement with the previous theoretical and experimental data. As far as we know, for the first time we find the effects of temperature and pressure on thermal parameters of CuAlTe₂ and CuGaTe₂ compounds. Thermal properties are very useful for optimizing crystal growth, and predict photovoltaic applications on extreme thermodynamic conditions.

The mechanical, electronic and thermodynamic properties of Pd₃M (M=Sc, Y) compounds have been investigated using the Full Potential Linearized Augmented Plane Wave (FP-LAPW) formalism. The generalized gradient approximation (GGA) is used to treat the exchange–correlation terms. The calculated formation enthalpies and the cohesive energies reveal that the L1₂ structure is more stable than the D0${}_{24}$ one. The obtained lattice parameters and bulk modulus calculations conform well to the available experimental and theoretical results. The elastic and mechanical properties are analyzed and results show that both compounds are ductile in nature. The Debye temperature and melting temperature are also estimated and are in a good agreement with experimental findings. The total and partial densities of states are determined for L1₂ and D0${}_{24}$ structures. The density of states at the Fermi level, $N$($E_{\mathrm{\text{F}}}$), indicates electronic stability for both compounds. The presence of the pseudo-gap near the Fermi level is suggestive of formation of directional covalent bonding. The number of bonding electrons per atom $n_b$ and the electronic specific heat coefficient $\gamma$ are also determined. The quasi-harmonic Debye model has been used to explore the temperature and pressure effects on the thermodynamic properties for both compounds.

An full potential linearized augmented plane wave (FP-LAPW)-based analytical study of structural, electronic, mechanical and thermoelectric properties has been done for the Ruthenium-based half heusler RuTiX (X = Si, Ge and Sn) compounds. An efficient method to develop Half Heusler (HH) alloys is by examining their stability of structure in various phases, by plotting electronic band structures, computing elastic constants and also by studying the presence of magnetic moments. In this study, we have used DFT-based calculations to scrutinise the paramagnetic/ferromagnetic (FM) as well as metallic/semiconducting behavior of these HH compounds. The predicted phase stability using the energy versus volume curves reveals that they are stable in Type C phase. RuTiSi and RuTiGe are found to be stable in the paramagnetic phase whereas RuTiSn is stable in the FM phase with a finite value of magnetic moment. The electronic band structures and density of states (DOS) plots predict that the studied compounds belong to $p$-type degenerate semiconductors as the Fermi Level lies within the valence band. Due to the existence of finite DOS at the Fermi level, they show an enhanced metallic behavior. A small value indirect gap is found between valence band maximum (VBM) and conduction band minimum (CBM) in all these studied RuTiX HH alloys depicting their semiconducting nature. The elastic constants of cubic phase are computed for the first time and they obey the mechanical stability criteria. The positive value of $C_{12}-C_{44}$ and value of $B$/$G_H$ ratio of these HH compounds exhibit their ductile nature. The thermoelectric properties of these compounds are investigated, and a comparatively higher figure of merit reveals their scope of application in thermoelectric devices.