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A comprehensive examination of the crystal structure, as well as elastic and thermal properties, of the recently created Zintl phase CsGaSb2 has been carried out using ab initio density functional theory pseudo-potential plane-wave calculations. All the provided facts presented are newly forecasted, with the exception of the structural properties under normal conditions. The calculated lattice parameters and interatomic bond lengths of the investigated material closely correspond to the actual values, indicating a high level of accuracy. Forecasts have been generated for the elastic parameters and related characteristics of both single-crystal and polycrystalline phases of CsGaSb2. The parameters encompassed in this list are elastic constants, shear modulus, bulk modulus, Poisson's ratio, Young's modulus, anisotropy indices, elastic wave velocities, Pugh's criterion, and Debye temperature. The mechanical and dynamic stability of CsGaSb2 as well as its elastic anisotropy have been established. The temperature dependence of various macroscopic properties, including bulk modulus, unit cell volume, volumetric thermal expansion coefficient, isochoric and isobaric thermal capacities, Debye temperature, Grüneisen parameter, and entropy function, was evaluated at specific pressures using Debye's quasi-harmonic approach in combination with ab initio calculations. [ABSTRACT FROM AUTHOR]

Intense UV emission is observed in Ce3+-doped GdBO3 nanophosphor, successfully prepared by simple sol gel method. The synthetized nano-powder sample is characterized by diffractometry (XRD) and room temperature steady photoluminescence. The XRD analysis shows that the crystallite size is 55 nm and crystallizes in the vaterite structure. The room temperature excitation and emission observed bands are assigned to 4f ↔ 5d inter-configurational transitions and investigated. First principal Density Functional theory DFT + U calculations, implemented in VASP code was used to performed the study of the structural and electronic structure of GdBO3:Ce3+ nanomaterial system in both vaterite P63/mmc and calcite R-3C. The U parameter is varied to give best 4f Ce position in GdBO3 bandgap. Also, it was found that the R-3C is the ground state crystalline structure and that the observed P63/mmc is higher in energy by about 0.1 eV/atom. By comparison between experimental and calculations results energy Ce3+ energy levels scheme relative to electronic band structure was constructed. [ABSTRACT FROM AUTHOR]

This study uses density functional theory calculations to study the impact of pressure on the structural, elastic, and thermodynamic properties of CaRh2P2 and BaRh2P2 compounds. The equilibrium structural parameters closely match the experimental values. CaRh2P2 shows a greater reduction in lattice parameter "a" under pressure, while BaRh2P2 shows the opposite trend. The single-crystal elastic constants calculated for both compounds meet the criteria for mechanical stability under varying pressures up to 18 GPa. The study extends to polycrystalline elastic properties, including bulk modulus, shear modulus, Young's modulus, Poisson's ratio, and related properties, under pressures up to 18 GPa. The Pugh ratio, Cauchy pressure, and Poisson's ratio indicate the ductile behavior of the title compounds. BaRh2P2 exhibits superconducting characteristics, unlike CaRh2P2, confirmed by interlayer PP bond length calculations. Debye's quasi-harmonic model explores the temperature dependencies of various properties, with results that align well with elastic constant data, thus validating the results. [ABSTRACT FROM AUTHOR]

In this work, the WIEN2k computer code was used to investigate the structural, elastic, electronic, magnetic, optical, thermoelectric, and dynamic properties of the CoCrTe half-Heusler (HH) compound. The Full-Potential Linearized Augmented Plane Wave method and Density Functional Theory were both used in this work. To further understand the electronic band gap, we used the modified Becke Johnson exchange–correlation functional method. We investigated the CoCrTe HH compound's electronic characteristics using density of states plots and band structure plots. By calculating magnetic moments and observing the behavior of spin-polarized electronic states, we also investigated the magnetic properties. Additionally, the CoCrTe HH compound's elastic properties were identified. These characteristics, including stiffness, resilience, and overall stability, offer crucial information about how the material reacts to mechanical deformation. Properties studied emphasized that the compound is metallic, and it appears as a good thermoelectric material. Finally, the compound's dynamic properties show that it is dynamically stable as well as mechanically. [ABSTRACT FROM AUTHOR]

The structural, elastic, electronic, magnetic, thermoelectric, and dynamic properties of the CoCrSe half-Heusler compound were examined using the WIEN2k code. Calculations were carried out in this work using the full-potential linearized augmented plane-wave (FP-LAPW) approach and density functional theory (DFT). We used modified Becke–Johnson (mBJ) exchange–correlation functional to improve the electronic energy bandgap. We studied different electronic properties of the CoCrSe compound, including density of states (DOS) and band structure plots. We also investigated the magnetic characteristics by computing magnetic moments and examining the behavior of spin-polarized electronic states. In addition, the elastic characteristics of the CoCrSe compound were determined. These properties, such as stiffness, resilience, and general stability, provide vital insights into the material’s response to mechanical deformation. The calculated elastic constants indicate that CoCrSe it is mechanically stable, brittle, and anisotropic. On the other hand, the compound is dynamically stable. Finally, we also check the thermoelectric properties. [ABSTRACT FROM AUTHOR]

The primary objective of this study is to investigate the influence of spin-orbit coupling and atom type on the electronic, optical, and thermoelectric properties of LuXNi2Sn2 (X = V, Nb, and Ta) double-half Heusler alloys. To achieve this, calculations were performed using the full potential linearized augmented plane wave method within the framework of density functional theory. Both full relativistic and scalar relativistic calculations were employed. The exchange-correlation interactions in this study were modeled using the PBEsol version of the generalized gradient approximation when calculating the structural ground state parameters. For the analysis of electronic, optical, and thermoelectric properties, the modified Becke–Johnson potential was employed. The modified Becke–Johnson potential was specifically chosen for its capability to improve the description of band gaps, particularly for systems with small band gaps, such as the LuXNi2Sn2 (X = V, Nb, and Ta) double-half Heusler materials examined in this study. This potential offers a more accurate representation of the electronic properties, enabling a more reliable analysis of the optical and thermoelectric characteristics of the materials under investigation. The examined LuXNi2Sn2 (X = V, Nb, and Ta) materials exhibit semiconductor behaviour, with band gaps smaller than 0.4 eV that can be controlled by varying the "X" atom. The charge carriers, specifically holes and electrons, exhibit light effective masses, indicating high mobility. Furthermore, these compounds exhibit low thermal expansion coefficients and satisfy the criteria for thermodynamic stability. In terms of optical properties, they display substantial absorption coefficients in the ultraviolet (UV) light region, high optical conductivity, and high reflectivity in the visible light region. Considering their favourable power factor and figure of merit characteristics, the LuXNi2Sn2 (X = V, Nb, and Ta) materials possess the potential to be promising candidates for thermoelectric applications. [ABSTRACT FROM AUTHOR]

A theoretical study was conducted to analyze electronic, elastic, and thermodynamic properties and the structural stability of the intermetallic materials Al3Ti1−xZrx for tetragonal-D022 and cubic-L12 structures carried out based on DFT. The findings indicate that the D022 phase has demonstrated more stability than the L12 phase and the possibility of a structural phase transition under pressure effect for concentrations x = 0.25 and x = 0.5. With increasing x concentration, the resulting lattice parameters drop. The density of states at the Fermi level, determines the electronic stability exhibited by these compounds. A pseudo-gap in proximity to the Fermi level implies the establishment of directional covalent bonding. The electronic structures support the phase stability results and show that the bonding in these compounds is more directed. Measurement techniques are employed to determine the number of bonding electrons per atom and the coefficient of electronic-specific heat. Both the mechanical as well as elastic properties of the considered alloys are examined. The findings demonstrate that all explored alloys are brittle, and D022 phase is stiffer than the L12 phase. The thermal characteristics are predicted via the quasi-harmonic Debye model. [ABSTRACT FROM AUTHOR]

This paper presents an investigation of the properties of the double half Heusler alloy (DHH) K2NaRbAs2. The structural, elastic, electronic, magnetic, and thermoelectric properties of the alloy are studied using the full-potential linearized augmented plane wave method (FP-LAPW) with the generalized gradient GGA approximation, and the GGA + Modified Becke-Johnson (mBJ) correlation potential is used to calculate the band structures and densities of states. The K2NaRbAs2 DHH alloy is derived from the previously studied parent half Heusler alloys KNaAs and KRbAs in their ferromagnetic phase of type I structure (FM-I). Our findings confirm the thermodynamic stability and synthesizability of K2NaRbAs2 in normal conditions. The alloy is shown to be resistant to distortion and able to withstand reversible deformation. The calculated elastic constants indicate that K2NaRbAs2 is mechanically stable, ductile, and anisotropic, as confirmed by 3D representation of its elastic moduli. Furthermore, the total magnetic moment of 2 µB demonstrates its half-metallic behavior, which mainly due to arsenic atoms. Like its parent alloys KNaAs, and KRbAs, the K2NaRbAs2 DHH alloy could be suitable for use in spintronic technology. Additionally, the thermoelectric characteristics of the K2NaRbAs2 DHH alloy are investigated using semi-classical Boltzmann transport theory, based on a smoothed Fourier interpolation of the bands, as implemented in the BoltzTraP package. [ABSTRACT FROM AUTHOR]

Recently, photovoltaic solar cells have been revolutionized by adopting ABX3 halide perovskite materials as photoabsorbers. In the recent past, lead halide perovskites have attracted significant research interest. However, owing to its toxicity, alternative lead-free materials are currently being actively sought. In this work, we report the computational results of the structural, electronic, optical and elastic properties of the unexplored lead-free halide fluoroperovskite material ASiF3 (A = Li, Na, K and Rb) by means of first-principles calculations. The computed energetic and elastic properties assert that the formation of the ASiF3 cubic systems is energetically favourable and mechanically stable. According to the results, LiSiF3 and NaSiF3 are indirect bandgap semiconductors, which are not appropriate for solar cell applications. The calculated elastic, electronic and optical properties indicate that KSiF3 and RbSiF3 alloys are isotropic and exhibit high ductility. They have reasonable direct bandgaps, a small effective mass and good light absorption, making them suitable for single-junction photovoltaic cells and other optoelectronic applications in the visible and UV regions of the electromagnetic spectrum. [ABSTRACT FROM AUTHOR]

Technological development cannot take place without a deep knowledge of materials and their physical properties. Complex oxides constitute a family of materials characterized by specific characteristics prompting them for potential technological applications. The results of a theoretical study related to the structural, thermodynamic, electronic, optical, and magnetic properties of the Dy2Be2GeO7 complex oxide are presented. The current study is accomplished using the "Full Potential (FP) Linearized (L) Augmented Plane Wave Plus Local Orbitals (APW + lo)" formalism as incorporated in the WIEN2k computational code in the "density functional theory" framework. To approximate the exchange and correlation effects, the PBE-GGA formalism of the "generalized gradient approximation" is used. Furthermore, "Tran-Blaha modified Becke–Johnson potential" is used to better describe the electronic structure. The equilibrium structural parameters are in good agreement with the corresponding measured data reported in the literature. The thermodynamic properties of the title compounds are explored via the quasi-harmonic approximation over temperature and pressure ranges from 0 to 700 K and 0 to 10 GPa, respectively. The electronic properties are determined with spin-polarized inclusions. Finally, the optical properties are examined with a detailed discussion of different optical parameters, including dielectric function, absorption coefficient, optical conductivity, reflectivity, and refractive index spectra. The Dy2Be2GeO7 complex oxide with a non-centrosymmetric tetragonal structure shows a negative birefringent, therefore it is a possible candidate for applying to the birefringent field and nonlinear optical process. To our best knowledge, the current study is the first effort to explore the physical characteristics of the considered complex oxide. [ABSTRACT FROM AUTHOR]

The optimized structural parameters, electronic structure, and thermoelectric coefficients of the chalcopyrite alloys Cu1–xNaxTlSe2, with x = 0.00, 0.25, and 0.50 were studied through density functional theory calculations. The Wu–Cohen generalized gradient and the Tran–Blaha modified Becke–Johnson approximations have been employed to describe the exchange–correlation potential. Energy band structure analysis reveals that CuTlSe2 is a semi-metal, while Cu0.25Na0.75TlSe2 and Cu0.50Na0.50TlSe2 alloys are semiconductors with gaps of approximately 0.17 eV and 0.35 eV, respectively. The total and partial densities of states were calculated and discussed. Examining the charge density, we point out the formation of the Na–Se ionic bond when Cu is replaced by the Na atom, which is responsible for the metal–semiconductor transition in the Cu1–xNaxTlSe2 alloys. Moreover, variations of the Seebeck coefficient, electrical conductivity, electronic and lattice thermal conductivity, power factor, and figure of merit of the Cu1–xNaxTlSe2 alloys with temperature and chemical potential were explored. The obtained results show that the value of the figure of merit increases when doping CuTlSe2 with sodium to reach 0.46 and 0.87 for p-type Cu0.75Na0.25TlSe2 and n-type Cu0.50Na0.50TlSe2, respectively. [ABSTRACT FROM AUTHOR]

This paper investigates in detail the structural, magnetic, and optoelectronic properties of Cd0.75TM0.25S (TM = Os and Ir) alloys having a zinc-blende structure of the ferromagnetic phase using the full potential linearized augmented plane-wave (FP-LAPW) method as implemented in the Wien2k package. The exchange–correlation potential was treated with the generalized gradient approximation (GGA). Moreover, the GGA + U + SO approximation (where U denotes the Hubbard Coulomb energy and SO is the spin orbit coopling) are employed to treat the d electrons properly. The analysis of the values of formation energy, formation enthalpy, phonon spectra and the exchange interaction parameters show that the investigated alloys are stable and can be synthesized. The densities of states (DOS) indicate that Cd0.75TM0.25S (TM = Os and Ir) exhibits metallic nature using both GGA and GGA + SO. The half-metallic nature for Cd0.75Os0.25S and the ferromagnetic half-semiconductor nature for Cd0.75Ir0.25S have been predicted by GGA + U. Both considered alloys become ferromagnetic-semiconductors by using GGA + SO + U, where the computed band gaps are 0.52 for Cd0.75Os0.25S and 0.72 for Cd0.75Ir0.25S. The dielectric function's real and imaginary portions ε ′ ω , ε ″ ω , absorption coefficient α (ω) , and refractive index n (ω) were evaluated using a radiation range up to 30 eV. For CdS, the observed results are on par with previously published experimental and theoretical results. Our findings imply that these materials might be of potential use in future spintronic devices. [ABSTRACT FROM AUTHOR]

The structural, elastic and thermodynamic properties of CaRu2As2 and CaRu2P2 under pressure effect up to 18 GPa were determined through density functional theory calculations. The calculated equilibrium lattice parameters are in good agreement with the available experimental findings. The computed single-crystal elastic constants show that the title compounds are mechanically stable in all the considered pressure range (0–18 GPa). The title compounds exhibit a strong elastic anisotropy. Pressure-dependence of the single-crystal elastic constants and polycrystalline elastic moduli, namely bulk modulus, shear modulus, Young's modulus and Poisson's ratio, was successfully determined. Debye temperature, average sound velocity, minimum thermal conductivity (Kmin), Vickers hardness (HV) and melting temperature (Tm) of the title compounds were calculated for a pressure range from 0 to 18 GPa. [ABSTRACT FROM AUTHOR]

In this study, an analysis of the effect of Na substitution on the electronic, structural and thermoelectric (TE) properties of the Li2CuAs material is presented. The study is performed by employing the full-potential linearized augmented plane wave plus local orbital method designed within the density functional theory. To carry out the calculations related to the band structure, generalized gradient approximation by Wu-Cohen (WC-GGA) in combination with Trans Blaha-modified Becke-Johanson mBJ (TB-mBJ) potential is employed. Our results at the level of the WC-GGA approach show that there is no bandgap, whereas, at the level of the TB-mBJ approximation, the material displays bandgap with Na substitution, which is found to be further increased with the increasing Na concentration. To understand the role of different electronic states on the bandgap structure, the total and partial densities of states are also analysed. Furthermore, the temperature effect on the Seebeck coefficient, electronic thermal conductivity, electrical conductivity, power factor and figure of merit are computed. Our obtained results of the TE properties of Li2CuAs at different Na compositions suggest that this compound is a potential candidate for thermoelectricity. [ABSTRACT FROM AUTHOR]

Following recent computational discovery of the Cs2InSbCl6 and Cs2InBiCl6 compounds, density functional theory screening of their fundamental physical properties is warranted to establish their potential as optoelectronic materials. Thus, in this paper, we report the results of detailed calculations of the structural, elastic, electronic, and optical properties of the Cs2InSbCl6 and Cs2InBiCl6 crystals using the full-potential augmented plane wave plus local orbitals method with the generalized gradient approximation (GGA) and Tran–Blaha modified Becke–Johnson potential (TB-mBJ) to model the exchange–correlation interactions. Calculations were performed both with and without including spin–orbit coupling effect. Ab initio molecular dynamics calculations show the thermal stability of the title compounds at 300 K. Predicted elastic constants show that the studied materials exhibit moderate resistant to external stress, strong elastic anisotropy, ductile nature, and mechanical stability. Cs2InSbCl6 and Cs2InBiCl6 are direct bandgap (Г–Г) semiconductors. Calculated optical properties reveal that the title compounds are characterized by strong absorption in a large energy window including the high-energy part of the sun visible spectrum. [ABSTRACT FROM AUTHOR]

Motivated by the growing demand for new performant semiconducting materials, we investigated in detail the structural, elastic, electronic and optical properties of two newly synthesized compounds, namely Tl2CdGeSe4 and Tl2CdSnSe4, using density functional theory calculations. The calculations were performed relativistically, including the spin–orbit coupling (SOC). The computed equilibrium structural parameters are in excellent agreement with available measurements. Note that the calculations of all the considered properties were performed with the theoretically obtained equilibrium lattice parameters. The predicted monocrystalline and polycrystalline elastic constants reveal that the studied compounds are soft, ductile, mechanically stable and substantially structurally and elastically anisotropic materials. Our calculations using the Tran-Blaha modified Becke-Johnson potential with the inclusion of SOC show that Tl2CdGeSe4 and Tl2CdSnSe4 are direct bandgap semiconductors. The inclusion of SOC is found to reduce the fundamental bandgap of Tl2CdGeSe4 from 1.123 to 0.981 eV and that of Tl2CdSnSe4 from 1.097 to 0.953 eV. The l-decomposed atom-projected densities of states were calculated to identify the contribution of each constituent atom to the electronic states in the energy bands. The upper valence subband predominantly comes from the Se-4p states, while the bottom of the conduction band mainly originates from the Se-4p and Ge-4p/Sn-5p states. The frequency-dependent linear optical parameters, viz., the complex dielectric function, absorption coefficient, refractive index, reflectivity and energy-loss function, were calculated for electromagnetic waves polarized parallel and perpendicular to the c-axis in a wide energy window. An attempt was made to identify the microscopic origin of the peaks and structures observed in the calculated optical spectra. [ABSTRACT FROM AUTHOR]

In this work, first-principles calculations were utilised to study the structural, magnetic and electronic properties of Mn 2 PtZ (Z = V, Co) based on density functional theory (DFT). These compounds are predicted to be more stable in the Cu 2 MnAl structure and the FM ground state is energetically favourable, with magnetic moments of 4.93 and 9.04 μ B / f.u. for Mn 2 PtV and Mn 2 PtCo compounds, respectively. Additionally, the computed total magnetic moments of both compounds agree well with the Slater–Pauling rule, M T = N V - 24, and the main contribution in these magnetic moments emanates from Mn atoms for both materials. Through the results on the spin-polarised electronic properties (band structures and densities of states), it is found that both alloys reveal a complete half-metallic (HM) character with a half-metallic gap using GGA + U + TB-mBJ approximation. [ABSTRACT FROM AUTHOR]

The first-principle calculations of density functional theory were used to study the structural, electronic, magnetic, mechanic, and half-metallic behavior of Y2MnZ (Z = Al, Ga, In) within the spin generalized gradient approximation. These compounds can be experimentally synthesized due to their negative values of the calculated formation energies. Our calculations indicate that they are more stable in Cu2MnAl-type structure. The Hg2CuTi-type structure displays half-metallic characteristic with 100% spin polarization at the Fermi level. The value of calculated magnetic moment has an integer value of 2μB for Y2MnZ (Z = Al, Ga, In) in the Hg2CuTi-type structure which well matches with magnetic moments predicted from Slater–Pauling rule. Therefore, the Y2MnZ (Z = Al, Ga, In) in the Hg2CuTi-type structure is predicted to be a candidate for possible spintronics applications. [ABSTRACT FROM AUTHOR]

Spin-coating technique is employed to deposit nanostructured zinc oxide (ZnO) doping aluminium (Al) on p-Si substrate. Atomic forces microscopy (AFM), X-ray diffraction (XRD), ultraviolet–visible (UV–Vis) and scanning electron microscopies (SEM) are utilized to investigate the influence of annealing temperature in the range of 200 to 600°C on the morphological, optical, structural and topographical characteristics of Al NPs-doped ZnO (AZO) nanostructure. The average reflectance is proven by the reflectance spectra to be in the wavelength range of 200–1000 nm, and the absorption spectra provided the optical energy gaps of nanostructured AZO. Crystalline and grain size are correlated with annealing temperature variations, thus providing more homogeneous and covered surface morphology. Our results are nominated for future researches. [ABSTRACT FROM AUTHOR]

A theoretical study of the structural, elastic, electronic, optical, magnetic, and thermoelectric properties of the newly synthetized diamond-like quaternary semiconductor CuMn2InSe4 was carried out in this paper. The calculated equilibrium structural parameters are in excellent agreement with available experimental data. The single-crystal and polycrystalline elastic moduli were predicted using energy strain technique. Electronic properties, including band energy dispersion, total and projected densities of states, and charge distribution map, were calculated and analyzed. Total and local magnetic moments were determined. Linear optical functions were predicted from the calculated band structure. We studied the chemical potential dependence of the thermoelectric parameters, including Seebeck coefficient, electrical conductivity, thermal conductivity, and power factor. The maximum power factor and the corresponding chemical potential are estimated. The obtained results were compared with available ones. [ABSTRACT FROM AUTHOR]

Owing to the fact of the AB2O4 spinel oxide’s chemical and thermal stability, and other intriguing properties make them suitable candidate materials for many applications, including chemical looping and catalytic reactions. To do our investigations, a short-range non-Coulomb potential theoretical model is used to calculate the zone-centre, elastic constants, infrared phonon mode frequencies, Raman phonon mode frequencies, velocities of the sound wave along the highly symmetric three crystallographic-axes and Debye temperature of the vanadium spinel oxides AV2O4 (A = Mn, Fe and Zn). The preliminary results of our calculations show that the interaction in the second neighbour (V–O) is much stronger than the interaction of the first neighbour (A–O). Moreover, from the analysis of the obtained results of elastic constants, the nature of the studied vanadium spinels are found to be ductile. [ABSTRACT FROM AUTHOR]

Through using spin coating technique, Cu2CdSnS4 (CCTS) quaternary alloy nanostructures were successfully deposited on GaN substrate using a wide range of spin coating speeds; 1500, 2000, 2500, 3000 and 3500 RPM at annealing temperature 300 °C. The optical properties were investigated through UV-vis which revealed the changing of energy band gap as the spin coating speed increases, in addition, to verify specific models of refractive index and optical dielectric constant. The structural properties were studied by X-ray diffraction which indicated that the number and intensity of the peaks were changed as the spin coating speed changes. The morphological and topographical studies of CCTS were elaborated by field emission-scanning electron microscopy and atomic force microscopy. The obtained results suggest that CCTS nanostructures deposited on GaN substrate are very suitable for optoelectronic applications, that are in accordance with the available theoretical and experimental data. [ABSTRACT FROM AUTHOR]

We report a detailed investigation of the elastic moduli, electronic band structure, density of states, chemical bonding, electron and hole effective masses, optical response functions and thermoelectric properties of the lead-free halide double perovskites CsAgBiCl and CsAgBiBr using the full potential linearized augmented plane wave (FP-LAPW) method with the generalized gradient approximation (GGA-PBEsol) and the Tran-Blaha modified Becke-Johnson (TB-mBJ) potential. Because of the presence of heavy elements in the studied compounds, we include the spin-orbit coupling (SOC) effect. Our calculated structural parameters agree very well with the available experimental and theoretical findings. Single-crystal and polycrystalline elastic constants are predicted using the total-energy versus strain approach. Three-dimensional representations of the crystallographic direction dependence on the shear modulus, Young's modulus and Poisson's ratio demonstrate a noticeable elastic anisotropy. The TB-mBJ potential with SOC yields an indirect band gap of 2.44 (1.93) eV for CsAgBiCl (CsAgBiBr), in good agreement with the existing experimental data. The chemical bonding features are probed via density of states and valence electron density distribution calculations. Optical response functions were predicted from the calculated band structure. Both of the investigated compounds have a significant absorption coefficient (∼ $$ 25 \times 10^{4} \;{\hbox{cm}}^{ - 1} $$ ) in the visible range of sunlight. The thermoelectric properties of the title compounds were investigated using the FP-LAPW approach in combination with the semi-classical Boltzmann transport theory. The CsAgBiCl and CsAgBiBr compounds have a large thermopower S, which makes them potential candidates for thermoelectric applications. [ABSTRACT FROM AUTHOR]

The full-Heusler alloys CoYZ (Z = P, As, Sb, and Bi) were investigated by using the state-of-the-art full-potential linearized augmented plane wave plus local orbital (FP-LAPW + lo) method within the framework of density functional theory (DFT), to understand the structural, electronic, and magnetic properties of these new Heusler alloys. The generalized gradient approximation (GGA) was chosen to define the exchange-correlation potential for studying the structural properties, whereas electronic and magnetic properties were developed by using the GGA + U scheme, where U is the Hubbard term, which explains the Coulomb repulsion and was applied to describe the ' d' electrons. The structural properties indicated that the ferromagnetic states of these compounds are energetically more favorable than the paramagnetic states. Through results on the electronic structures (band structures and densities of states), it is found that all these alloys exhibit a complete half-metallic nature, with half-metallic gaps (E) of 0.632, 0.605, 1.223, and 0.922 eV for CoYP, CoYAs, CoYSb, and CoYBi alloys, respectively. The magnetic properties indicated that the total spin magnetic moments of these Heusler alloys obey the Slater-Pauling rule around value 2 µ approximately. The local magnetic moments of Co and Y transition elements have opposite signs with different intensities, thus revealing the ferromagnetic character. Our study of both electronic and magnetic properties demonstrates in detail that CoYZ (Z = P, As, Sb, and Bi) full-Heusler alloys are complete half-metallic ferrimagnetic materials. [ABSTRACT FROM AUTHOR]

We report the results of the full-potential linearized augmented plane wave (FP-LAPW) calculations on the structural, elastic, optoelectronic and magnetic properties of $$\hbox {CdHo}_{2}\hbox {S}_{4}$$ spinel. Both the generalized gradient approximation (GGA) and Trans-Blaha modified Becke-Johnson potential (TB-mBJ) are used to model the exchange-correlation effects. The computed lattice parameter, internal coordinate and bulk modulus are in good agreement with the existing experimental data. According to the calculated elastic moduli, $$\hbox {CdHo}_{2}\hbox {S}_{4}$$ is mechanically stable with a ductile nature and a noticeable elastic anisotropy. The ferromagnetic phase of $$\hbox {CdHo}_{2}\hbox {S}_{4}$$ is energetically favourable compared to non-magnetic one, with a high magnetic moment of about 8.15 $$\upmu _{\mathrm{B}}$$ . The calculated band structure demonstrates that the title compound is a direct band gap semiconductor. The TB-mBJ yields a band gap of $$\sim $$ 1.86 and $$\sim $$ 2.17 eV for the minority and majority spins, respectively. The calculated optical spectra reveal a strong response in the energy range between the visible light and the extreme UV regions. [ABSTRACT FROM AUTHOR]

The electronic structures and magnetic properties of KO and RbO alloys doped simultaneously with Cr and V transition elements were investigated using the full-potential linearized augmented plane wave plus local orbital (FP-LAPW + lo) method within the spin-polarized density functional theory (Spin-DFT) and implemented in the WIEN2k package, where the exchange-correlation potential in this approach is described by the generalized gradient approximation with Coulomb repulsion (GGA + U). The substitution of transition metals at 25 % ratio yields the magnetic characteristic of half-metallic ferromagnetism for KO and RbO alloys. The structural properties were estimated in both magnetic and non-magnetic phases, demonstrating the stable ferromagnetic ground phase. The analysis of the electronic structure reveals the excellent half-metallic ferromagnetic nature, with a clear half-metallic gap ( E ) of 0.20 eV for KCrO alloy. The exploitation of the electronic structure mainly served to determine the spin-polarized exchange-splitting energies Δ( d) and Δ( pd) generated by 3d-TM states, shows that the effective potential of the minority spin is more attractive than that of the majority spin. Moreover, the s− d exchange constant N α (conduction band) and p− d exchange constant N β (valence band) describe their contributions during the exchange splitting process. The magnetic properties have indicated that these alloys acquire a magnetic moment when the non-magnetic system is doped with a transition metal (TM). The obtained results from the important magnetic moments of these alloys indicate the potential for their use in spintronic devices. [ABSTRACT FROM AUTHOR]

Lattice dynamics calculations have been performed for ternary chalcopyrite compounds CuAlS, CuGaS, CuInS, and AgGaS using the proposed theoretical model. This model is applied to study the zone-centre (GAMMA = 0) phonon frequencies of CuAlS, CuGaS, CuInS, and AgGaS. The interatomic interactions up to third nearest neighbours were calculated. The calculated zone-centre phonon frequencies are found to be in very good agreement with observed and previous calculated data available in the literature. Single crystal elastic constants and related properties for these materials were also calculated and compared with the available data in the scientific literature. [ABSTRACT FROM AUTHOR]

First-principles density functional calculations were performed to investigate the structural parameters, elastic moduli and related properties, electronic band structure and optical properties of three LaOAgS-type barium silver fluoride chalcogenides BaAg ChF ( Ch denotes the chalcogenides S, Se and Te). The calculated structural parameters are in good accordance with the existing experimental data. The single-crystal and polycrystal elastic moduli were determined via the strain-stress technique. The investigated compounds show a strong anisotropic behaviour of the structural and elastic parameters. The calculated electronic band structure using the Tran-Blaha modified Becke-Johnson potential reveals that the three considered systems are large direct band gap semiconductors. The assignments of the energy band electronic states and chemical bonding character were accomplished with the help of the l-decomposed atomic densities of states diagrams. Frequency-dependent polarized optical functions were computed for an energy range from 0 eV to 30 eV. The microscopic origin of the electronic states that is responsible for the optical spectra structures were determined. The optical spectra exhibit a considerable anisotropy. Several trends in the variation of the considered physical properties with the atomic number Z of the chalcogenide Ch element in the BaAg ChF series are observed. [ABSTRACT FROM AUTHOR]

The authors describe an integrated biosensor for amperometric DNA detection of Dengue virus in real time. CuCdSnS (CCTS) quaternary alloy nanostructures were successfully synthesized, deposited on an oxygen-etched silicon substrate (O/Si) via spin coating, and annealed at 400 °C. The nanostructures were investigated by using UV-vis spectroscopy, X-ray diffraction, atomic force microscopy and scanning electron microscopy. Interdigitated electrodes were fabricated using silver as a metal contact deposited on the CCTS/O/Si substrate using a thermal evaporator vacuum coater and a hard mask. The quaternary alloy acts as a support for immobilization of a Dengue-specific DNA probe that is employed as the recognition element. Single-stranded DNA in concentrations from 100 f. to 10 nM were successfully recognized via amperometry, typically at a working voltage of 1.5 V. The lower detection limit is 17 nM. Sensitivity is found to be 24.2 μA nM cm. The biosensor is inexpensive, fast, highly sensitive, and has low power consumption. [ABSTRACT FROM AUTHOR]

The CuZnCdSnS quinternary alloy nanostructures with different Cd concentrations were grown using spin coating technique on n-type silicon (100) substrate, analysed and characterized by X-ray diffraction (XRD), Photoluminescence (PL) and Field Emission-Scanning Electron Microscopy (FE-SEM). The XRD peaks were shifted towards the lower angle side with increasing Cd concentration. The refractive index and optical dielectric constant are calculated. The electrical characterization of the Ag/n-Si/CuZnCdSnS/Ag diode through current to voltage (I-V) characterization shows the highest photo-response of (value if any) at CuZnCdSnS composition. The electrical characterization shows the highest photoresponse at CuZnCdSnS quinternary alloy. [ABSTRACT FROM AUTHOR]

The effect of pressure on the structural, elastic, and thermodynamic properties of SrTe in both B1 (rocksalt) and B2 (CsCl-type) phases and the SrTeCa alloys with Ca dopant concentrations at x = 0.16667, 0.20, 0.33333, 0.42857, 0.44444 and 0.50 have been investigated using the two new gradient-corrected functional developed by Perdew, J.P.; Burke, K.; Ernzerhof named Density-Gradient Expansion for Exchange in Solids (PBEsol) and generalized Wu-Cohen (WC), in a significant range of pressure from 0 GPa to 30 GPa. The structure parameters, elastic stiffness constants c , the bulk modulus ( B), Kleinman parameter ( $$ \xi $$ ), shear anisotropies A are also determined. Furthermore, as reported in this study, the aggregate elastic modulus ( B, G, E), Poisson's ratio ( ν) and the Lame's coefficients ( λ) are estimated. On the other hand, the ductility, brittleness, longitudinal, transverse sound velocities and the Debye temperature Θ( T) are also obtained. Importantly, our results are in reasonable agreement with the available theoretical and experimental data. To the best of our knowledge, this is the first study of the effect of the composition on the properties of the SrTeCa alloys which may encourage other works for the confirmation of the reported results. [ABSTRACT FROM AUTHOR]

We report the results of an ab initio study of the electronic, optical and thermodynamic properties of the LiBaP and LiSrP compounds using the pseudopotential plane-wave method within the framework of the density functional theory with the GGA-PBEsol. The calculated equilibrium structural parameters are in good agreement with the available experimental data. The energy band dispersions along the high symmetry directions in the k-space and the density of states diagrams are computed and analyzed. The obtained energy bands show that both examined crystals are indirect band gap semiconductors. The chemical bonding character is examined via electron density map plots. The optical properties are predicted for an incident radiation in an energy range up to 15 eV, and the origins of the main peaks in the optical spectra are discussed in terms of the calculated electronic band structure. We have also predicted the temperature and pressure dependencies of the unit-cell volume, thermal expansion coefficient, heat capacity, Debye temperature and Grüneisen parameter. [ABSTRACT FROM AUTHOR]

CdS nanostructures have grown on p-type silicon (Si) (100) substrates using sol-gel method. The crystalline quality, surface morphology, optical and electrical properties of the deposited CdS nanostructures have been characterized and analyzed using atomic force microscopy, scanning electron microscopy, X-ray diffraction, thermogravimetric analysis, differential thermal analysis, UV-vis spectroscopy and electrical characterization, respectively. The effect of annealing temperature in the range 200-600 °C on the structural, morphological, optical and electrical properties has been elaborated. The XRD analysis shows that the crystalline quality can be improved by increasing the temperature to 400 °C, but further increase to 600 °C leads to degradation of crystalline quality. The bulk modulus is calculated and showed good agreement with experimental and theoretical results. The optical properties of absorption, reflection, energy band gap and extinction coefficient are obtained by UV-vis spectroscopy. The calculated refractive index and optical dielectric constant have shown good agreement with other results. The electrical and thermal properties are studied for antireflection coating applications. [ABSTRACT FROM AUTHOR]

First-principles calculations of the structural, elastic, electronic, magnetic and thermodynamic properties of zinc blende BeVTe alloys ( x = 0, 0.25, 0.50, 0.75 and 1) based on spin-polarized density functional theory are performed using full-potential augmented plane wave method, within the spin generalized gradient approximation for the exchange-correlation potential. The equilibrium structural parameters such as lattice constant ( a), bulk modulus ( B) and first pressure derivative of bulk modulus ( $$ B^{\prime } $$ ) are optimized for all alloys. The elastic constants C, C, C and anisotropy coefficients are also estimated. The calculations of the band structure and the density of states demonstrate that all BeVTe ( x = 0.25, 0.50, 0.75 and 1) alloys are complete half-metals. The investigation of the band structure and the density of states demonstrate that BeVTe alloy is entirely half-metal, whereas BeVTe and BeVTe alloys are nearly half-metal. The estimation of the s( p)- d exchange splitting constants N (conduction band) and N (valence band), as obtained through the density of states, have been used to indicate the magnetic behavior of the compounds. From the total magnetic moment, it is observed that the p- d hybridization reduces the local magnetic moment of V atom from its free space charge of 3 µ and generates small local magnetic moments on the nonmagnetic Be and Te sites. Lastly, based on the quasi-harmonic Debye model, the obtained macroscopic thermodynamic properties, such as thermal expansion coefficient, heat capacities and Debye temperate, are presented in detail. [ABSTRACT FROM AUTHOR]

The structural, elastic, electronic, optical, and thermodynamic properties of the $$\hbox {ZnAl}_{2}\hbox {S}_{4 }$$ compound are calculated in the frame work of the density functional theory where the calculated structural parameters are found to be in good agreement with the experimental data and other theoretical calculations. The calculations show that the material is elastically stable and isotropic. Furthermore, the calculated band gap is observed to be wide and direct and is comparable with earlier experimental data as well as with other theoretical calculations; hence, it is an optically active material for optoelectronic applications. In addition, the compound is found to have mixed ionic and covalent bonding nature. The optical nature of the compound is described in terms of the complex dielectric function, complex refractive index, reflectivity, and energy loss function. On the other hand, variation of the unit cell volume, bulk modulus, heat capacity, and Debye temperature are described as a function of temperature at different pressures for the $$\hbox {ZnAl}_{2}\hbox {S}_{4}$$ compound. [ABSTRACT FROM AUTHOR]

Structural, elastic, electronic and mechanical properties of the MSi (M = Ti, Zr) compounds with (MnSi) 16H crystal structure have been studied with respect to pressure. Our computational method is based on a pseudo-potential plane-wave (PP-PW) method. The exchange correlation has been treated using the generalized gradient approximation (GGA) in order to work out the densities of states. Ground-state quantities, such as lattice parameter and bulk modulus, have been evaluated, as well as elastic constants and their pressure derivative. Elastic constants and their pressure dependence have been calculated. Also, bulk and shear moduli, Young's modulus and Poisson's ratio for ideal polycrystalline phases have been derived. [ABSTRACT FROM AUTHOR]

Structural parameters, electronic structure, elastic constants and thermodynamic properties of the tetragonal ternary intermetallics CaCuSi and SrCuSi are investigated theoretically for the first time using the plane-wave ultra-soft pseudopotential method based on the density functional theory. The calculated equilibrium structural parameters agree well with the existing experimental data. Pressure dependence of the structural parameters is also explored. Analysis of the band structure, total and site-projected l-decomposed densities of states and valence charge distributions reveals the conducting character of both considered materials with a mixture of ionic-covalent chemical bonding character. Pressure dependences of the single-crystal elastic constants C for CaCuSi and SrCuSi are explored. The elastic wave velocities propagating along the principal crystallographic directions are numerically estimated. The elastic anisotropy is estimated and further illustrated by 3D-direction-dependent of the Young's modulus. A set of some macroscopic elastic moduli, including the bulk, Young's and shear moduli, Poisson's coefficient, average elastic wave velocities and Debye temperature, were calculated for polycrystalline CaCuSi and SrCuSi from the C via the Voigt-Reuss-Hill approximations. Through the quasiharmonic Debye model, which takes into account the phonon effects, the temperature and pressure dependencies of the bulk modulus, unit cell volume, volume thermal expansion coefficient, Debye temperature and volume constant and pressure constant heat capacities of CaCuSi and SrCuSi are explored systematically in the ranges of 0-40 GPa and 0-1400 K. [ABSTRACT FROM AUTHOR]

We performed ab initio calculations using the FPLAW method with the local density approximation (LDA) implemented in the WIEN2 k code for the orthorhombic (α) and triclinic (β) phases of BiNbO. The modified Becke-Johnson exchange potential (mBJ)-LDA approach was also used to improve the electronic properties. The lattice constants calculated for both structures using the LDA are in good agreement with the experimental values. For the band structure calculations, the mBJ-LDA approach provides reasonable agreement for the band gap value compared with the LDA. The estimated (mBJ)-LDA band gap values are 2.89 eV (3.73 eV) and 2.62 eV (3.15 eV) for the α and β phases of BiNbO, respectively. Significant optical anisotropy is clearly observed in the visible-light region. We also calculated and evaluated the electron energy loss spectrum for BiNbO. This work provides the first quantitative theoretical prediction of optical properties and electron energy loss spectra for both the orthorhombic and triclinic phases of BiNbO. [ABSTRACT FROM AUTHOR]

Pseudopotential plane-wave method based on density functional theory within the generalized gradient approximation for the exchange-correlation potential has been applied to study the structural, electronic, elastic and vibrational properties of the binary intermetallic PdV and PtV in the L1 phase. The optimized lattice constant, bulk modulus and its pressure derivative, independent single-crystal elastic constants and elastic wave velocities in three different directions are evaluated and compared with the available experimental and theoretical data. The polycrystalline elastic parameters, hardness coefficient, elastic anisotropy, Debye temperature are estimated. The electronic band structure, electronic total and partial densities of states, and total magnetic moment of the PdV and PtV alloys are computed and analyzed in comparison with the existing theoretical and experimental findings. Phonon-dispersion curves and their corresponding total and projected densities of states were obtained for the first time using a linear-response in the framework of the density functional perturbation theory. [ABSTRACT FROM AUTHOR]

The mechanical, optoelectronic, and thermodynamic properties of carbon silicon nitride spinel compound have been investigated using density functional theory. The exchange-correlation potential was treated with the local density approximation (LDA) and the generalized gradient approximation of Perdew-Burke and Ernzerhof (PBE-GGA). In addition, the Engel-Vosko generalized gradient approximation (EV-GGA) and the modified Becke-Johnson potential (TB-mBJ) were also applied to improve the electronic band structure calculations. The ground state properties, including lattice constants and bulk modulus, are in fairly good agreement with the available theoretical data. The elastic constants, Young's modulus, shear modulus, and Poisson's ratio have been determined by using the variation of the total energy with strain. From the elastic parameters, it is inferred that this compound is brittle in nature. The results of the electronic band structure show that CSi2N4 has a direct energy band gap ( Γ- Γ). The TB-mBJ approximation yields larger fundamental band gaps compared to those of LDA, PBE-GGA, and EV-GGA. In addition, we have calculated the optical properties, namely, the real and the imaginary parts of the dielectric function, refractive index, extinction coefficient, reflectivity, and energy loss function for radiation up to 40.0 eV. Using the quasi-harmonic Debye model which considers the phononic effects, the effect of pressure P and temperature T on the lattice parameter, bulk modulus, thermal expansion coefficient, Debye temperature, and the heat capacity for this compound were investigated for the first time. [ABSTRACT FROM AUTHOR]

The structural, elastic, and thermodynamic properties of the cubic anti-perovskite $$\hbox {RBRh}_{3}$$ RBRh 3 (R = Sm, Eu, Gd, and Tb) compounds have been investigated using first principles full-potential augmented-plane wave plus local orbitals (FP-APW+lo) method with the generalized gradient approximation. The ground-state quantities such as the lattice parameter, bulk modulus, and its pressure derivative, as well as elastic constants are estimated. Computed equilibrium lattice constants agree well with the available experimental data. The full set of first-order elastic constants and their pressure dependence, which have not been calculated or measured yet, have been determined. The elastic moduli increase linearly with increasing pressure and satisfy the generalized elastic stability criteria for cubic crystals under hydrostatic pressure. The shear modulus, Young’s modulus, and Poisson’s ratio are calculated for ideal polycrystalline $$\hbox {RBRh}_{3}$$ RBRh 3 aggregates. The Debye temperature is estimated from the average sound velocity. From the elastic parameter behavior, it is inferred that cubic anti-perovskites $$\hbox {RBRh}_{3}$$ RBRh 3 are ductile in nature and that the bonding is predominantly of an ionic nature. Following the quasi-harmonic Debye model, the temperature effect on the lattice constant, bulk modulus, heat capacity, and Debye temperature is calculated reflecting the anharmonic phonon effects. [ABSTRACT FROM AUTHOR]

The elastic, electronic and thermodynamic properties of fluoro-perovskite KZnF have been calculated using the full-potential linearized augmented plane wave (FP-LAPW) method. The exchange-correlation potential is treated with the generalized gradient approximation of Perdew-Burke-Ernzerhof (GGA-PBE). Also, we have used the Engel and Vosko GGA formalism (GGA-EV) to improve the electronic band structure calculations. The calculated structural properties are in good agreement with available experimental and theoretical data. The elastic constants C are calculated using the total energy variation with strain technique. The shear modulus, Young's modulus, Poisson's ratio and the Lamé coefficients for polycrystalline KZnF aggregates are estimated in the framework of the Voigt-Reuss-Hill approximations. The ductility behavior of this compound is interpreted via the calculated elastic constants C. Electronic and bonding properties are discussed from the calculations of band structure, density of states and electron charge density. The thermodynamic properties are predicted through the quasi-harmonic Debye model, in which the lattice vibrations are taken into account. The variation of bulk modulus, lattice constant, heat capacities and the Debye temperature with pressure and temperature are successfully obtained. [ABSTRACT FROM AUTHOR]

Using First-principle calculations, we have studied the structural, electronic and elastic properties of M2TlC, with M = Ti, Zr and Hf. Geometrical optimization of the unit cell is in good agreement with the available experimental data. The effect of high pressures, up to 20 GPa, on the lattice constants shows that the contractions are higher along the c-axis than along the a axis. We have observed a quadratic dependence of the lattice parameters versus the applied pressure. The band structures show that all three materials are electrical conductors. The analysis of the site and momentum projected densities shows that bonding is due to M d-C p and M d-Tl p hybridizations. The M d-C p bonds are lower in energy and stiffer than M d-Tl p bonds. The elastic constants are calculated using the static finite strain technique. We derived the bulk and shear moduli, Young’s modulus and Poisson’s ratio for ideal polycrystalline M2TlC aggregates. We estimated the Debye temperature of M2TlC from the average sound velocity. This is the first quantitative theoretical prediction of the elastic properties of Ti2TlC, Zr2TlC, and Hf2TlC compounds that requires experimental confirmation. [ABSTRACT FROM AUTHOR]

We have investigated the structural, elastic, electronic, optical and thermal properties of c-SiGe2N4 by using the ultrasoft pseudopotential density functional method within the generalized gradient approximation. The calculated structural parameters, including the lattice constant, the internal free parameter, the bulk modulus and its pressure derivative are in agreement with the available data. The independent elastic constants and their pressure dependence, calculated using the static finite strain technique, satisfy the requirement of mechanical stability, indicating that c-SiGe2N4 compound could be stable. We derive the shear modulus, Young’s modulus, Poisson’s ratio and Lamé’s coefficients for ideal polycrystalline c-SiGe2N4 aggregate in the framework of the Voigt-Reuss-Hill approximation. We estimate the Debye temperature of this compound from the average sound velocity. Band structure, density of states, Mulliken charge populations and pressure coefficients of energy band gaps are investigated. Furthermore, in order to understand the optical properties of c-SiGe2N4, the dielectric function, refractive index, extinction coefficient, optical reflectivity and electron energy loss are calculated for radiation up to 40 eV. Thermal effects on some macroscopic properties of c-SiGe2N4 are predicted using the quasi-harmonic Debye model in which the lattice vibrations are taken into account. We have obtained successfully the variations of the primitive cell volume, volume expansion coefficient, heat capacities and Debye temperature with pressure and temperature in the ranges of 0–40 GPa and 0–2000 K. For the first time, the numerical estimates of the elastic constants and related parameters, and the thermal properties are performed for c-SiGe2N4. [ABSTRACT FROM AUTHOR]

Using ab initio calculations, we have studied the structural, electronic and elastic properties of M2GeC, with M=Ti, V, Cr, Zr, Nb, Mo, Hf, Ta and W. Geometrical optimizations of the unit cell are in agreement with the available experimental data. The band structures show that all studied materials are electrical conductors. The analysis of the site and momentum projected densities shows that bonding is due to M d-C p and M d-Ge p hybridizations. The elastic constants are calculated using the static finite strain technique. The shear modulus C44, which is directly related to the hardness, reaches its maximum when the valence electron concentration is in the range 8.41–8.50. We derived the bulk and shear moduli, Young’s moduli and Poisson’s ratio for ideal polycrystalline M2GeC aggregates. We estimated the Debye temperature of M2GeC from the average sound velocity. This is the first quantitative theoretical prediction of the elastic constants of Ti2GeC, V2GeC, Cr2GeC, Zr2GeC, Nb2GeC, Mo2GeC, Hf2GeC, Ta2GeC and W2GeC compounds, and it still awaits experimental confirmation. [ABSTRACT FROM AUTHOR]

We have investigated the structural, elastic, electronic, optical and thermal properties of c-SiGe2N4 by using the ultrasoft pseudopotential density functional method within the generalized gradient approximation. The calculated structural parameters, including the lattice constant, the internal free parameter, the bulk modulus and its pressure derivative are in agreement with the available data. The independent elastic constants and their pressure dependence, calculated using the static finite strain technique, satisfy the requirement of mechanical stability, indicating that c-SiGe2N4 compound could be stable. We derive the shear modulus, Young’s modulus, Poisson’s ratio and Lamé’s coefficients for ideal polycrystalline c-SiGe2N4 aggregate in the framework of the Voigt-Reuss-Hill approximation. We estimate the Debye temperature of this compound from the average sound velocity. Band structure, density of states, Mulliken charge populations and pressure coefficients of energy band gaps are investigated. Furthermore, in order to understand the optical properties of c-SiGe2N4, the dielectric function, refractive index, extinction coefficient, optical reflectivity and electron energy loss are calculated for radiation up to 40 eV. Thermal effects on some macroscopic properties of c-SiGe2N4 are predicted using the quasi-harmonic Debye model in which the lattice vibrations are taken into account. We have obtained successfully the variations of the primitive cell volume, volume expansion coefficient, heat capacities and Debye temperature with pressure and temperature in the ranges of 0–40 GPa and 0–2000 K. For the first time, the numerical estimates of the elastic constants and related parameters, and the thermal properties are performed for c-SiGe2N4. [ABSTRACT FROM AUTHOR]

We report theoretical calculations of the band structure and density of states for orthorhombic LiGaS (LGS) and LiGaSe (LGSe). These calculations are based on the full potential linear augmented plane wave (FP-LAPW) method within a framework of density functional theory. Our calculations show that these crystals have similar band structures. The valence band maximum (VBM) and the conduction band minimum (CBM) are located at Γ, resulting in a direct energy band gap. The VBM is dominated by S/Se-p and Li-p states, while the CBM is dominated by Ga-s, S/Se-p and small contributions of Li-p and Ga-p. From the partial density of states we find that Li-p hybridizes with Li-s below the Fermi energy ( E ), while Li-s/p hybridizes with Ga-p below and above E . Also, we note that S/Se-p hybridizes with Ga-s below and above E . [ABSTRACT FROM AUTHOR]

We report results of first-principles calculations for the electronic and optical properties under pressure effect of Li2O, Na2O, Ki2O and Rb2O compounds in the cubic antifluorite structure, using a full relativistic version of the full-potential augmented plane-wave plus local orbitals (FP-APW+lo) method based on density functional theory, within the local density approximation (LDA) and the generalized gradient approximation (GGA). Moreover, the alternative form of GGA proposed by Engel and Vosko (GGA-EV) is also used for band structure calculations. The calculated equilibrium lattices and bulk moduli are in good agreement with the available data. Band structure, density of states, and pressure coefficients of the fundamental energy gap are given. The critical point structure of the frequency dependent complex dielectric function is also calculated and analyzed to identify the optical transitions. The pressure dependence of the static optical dielectric constant is also investigated. [ABSTRACT FROM AUTHOR]

The results of first-principles theoretical study of the structural, electronic and optical properties of SrCl2 in its cubic structure, have been performed using the full-potential linear augmented plane-wave method plus local orbitals (FP-APW+lo) as implemented in the WIEN2k code. In this approach both the local density approximation (LDA) and the generalized gradient approximation (GGA) are used for the exchange-correlation (XC) potential. Also we have used the Engel-Vosko GGA formalism, which optimizes the corresponding potential for band structure calculations. We performed these calculations with and without spin-orbit interactions. Including spin-orbit coupling cause to lifts the triple degeneracy at Γ point and a double degeneracy at X point. Results are given for structural properties. The pressure dependence of elastic constants and band gaps are investigated. The dielectric function, reflectivity spectra and refractive index are calculated up to 30 eV. Also we calculated the pressure and volume dependence of the static optical dielectric constant. [ABSTRACT FROM AUTHOR]

Using first-principles density functional calculations, the effect of high pressures, up to 20 GPa, on the structural and elastic properties of Zr2AlX and Ti2AlX, with X = C and N, were studied by means of the pseudo-potential plane-waves method. Calculations were performed within the local density approximation to the exchange-correlation approximation energy. The lattice constants and the internal parameters are in agreement with the available results. The elastic constants and their pressure dependence are calculated using the static finite strain technique. We derived the bulk and shear moduli, Young's moduli and Poisson's ratio for ideal polycrystalline Zr2AlX and Ti2AlX aggregates. We estimated the Debye temperature of Zr2AlX and Ti2AlX from the average sound velocity. This is the first quantitative theoretical prediction of the elastic properties of Zr2AlC, Zr2AlN and Ti2AlN compounds, and it still awaits experimental confirmation. [ABSTRACT FROM AUTHOR]