The structural,electronic, elastic,vibration and thermodynamic properties of GdMg

We have investigated the structural, elastic, electronic, vibration and thermodynamic properties of GdMg alloy using the methods of density functional theory within the generalized gradient approximation (GGA) for the exchange-correlation functional. We have presented the results on the basic physical parameters, such as the lattice constant, bulk modulus, pressure derivative of bulk modulus with and without spin-polarization (SP), second-order elastic constants, Zener anisotropy factor, Poisson's ratio, Young's modulus, and isotropic shear modulus. The thermodynamic properties of the considered compound are obtained through the quasi-harmonic Debye model. In order to obtain further information, we have also studied the pressure and temperature-dependent behavior of the volume, bulk modulus, thermal expansion coefficient, heat capacity, and Debye temperature in a wide temperature range of 0–1200 K. We have also calculated phonon frequencies and one-phonon density of states for B2 structure of GdMg compound. The temperature-dependent behavior of heat capacity and entropy obtained from phonon density of states for GdMg compound in B2 phase is also presented.     

Structural,mechanical, electronic,and thermodynamic properties of pure tungsten metal under different pressures: A first-principles study

The structural, mechanical, electronic, and thermodynamic properties of pure W metal under different pressures have been investigated using the first-principles method. Our calculated structural parameters are in good agreement with experimental and previous theoretical results. The obtained elastic constants show that pure W metal is mechanically stable. Elastic properties such as the bulk modulus (B), shear modulus (G), Young's modulus (E), Poisson's ratio (ν), Cauchy pressure (C′), and anisotropy coefficients (A) are calculated by the Voigt-Reuss-Hill method. The results show that the pressure can improve the strength of pure tungsten and has little effect on the ductility. In addition, the total density of states as a function of pressure is analyzed. Thermodynamic properties such as the Debye temperature, phonon dispersion spectrum, free energy, entropy, enthalpy, and heat capacity are also discussed.     

First principles prediction of the elastic,electronic, and optical properties of Sb2S3 and Sb2Se3 compounds

We have performed a first principles study of structural, mechanical, electronic, and optical properties of orthorhombic Sb₂S₃ and Sb₂Se₃ compounds using the density functional theory within the local density approximation. The lattice parameters, bulk modulus, and its pressure derivatives of these compounds have been obtained. The second-order elastic constants have been calculated, and the other related quantities such as the Young's modulus, shear modulus, Poisson's ratio, anisotropy factor, sound velocities, Debye temperature, and hardness have also been estimated in the present work. The linear photon-energy dependent dielectric functions and some optical properties such as the energy-loss function, the effective number of valence electrons and the effective optical dielectric constant are calculated. Our structural estimation and some other results are in agreement with the available experimental and theoretical data.     

Structural,elastic, electronic and optical properties of the newly synthesized monoclinic Zintl phase BaIn2P2

The present study explores the structural, elastic, electronic and optical properties of the newly synthesized monoclinic Zintl phase BaIn₂P₂ using a pseudopotential plane-wave method in the framework of density functional theory within the generalized gradient approximation. The calculated lattice constants and internal coordinates are in very good agreement with the experimental findings. Independent single-crystal elastic constants as well as numerical estimations of the bulk modulus, the shear modulus, Young's modulus, Poisson's ratio, Pugh's indicator of brittle/ductile behaviour and the Debye temperature for the corresponding polycrystalline phase were obtained. The elastic anisotropy of BaIn₂P₂ was investigated using three different indexes. The calculated electronic band structure and the total and site-projected l-decomposed densities of states reveal that this compound is a direct narrow-band-gap semiconductor. Under the influence of hydrostatic pressure, the direct D–D band gap transforms into an indirect B-D band gap at 4.08 GPa, then into a B–Γ band gap at 10.56 GPa. Optical macroscopic constants, namely, the dielectric function, refractive index, extinction coefficient, reflectivity coefficient, absorption coefficient and energy-loss function, for polarized incident radiation along the [100], [010] and [001] directions were investigated.     

Structural, thermodynamic and optical properties of MgF2 studied from first-principles theory

A detailed theoretical study of structural, electronic, elastic, thermodynamic and optical properties of rutile type MgF₂ has been carried out by means of first-principles Density Functional Theory (DFT) calculations using plane wave pseudo-potentials within the local density approximation and generalized-gradient approximation for the exchange and correlation functionals. The calculated ground state properties and elastic constants agree quite well with experimental values. From the calculated elastic constants we conclude that MgF₂ is relatively hard when compared to other alkaline-earth fluorides and ductile in nature. The thermodynamic properties such as heat capacity, entropy, free energy, phonon density of states and Debye temperatures are calculated at various temperatures from the lattice dynamical data obtained through the quasi-harmonic Debye model. From free energy and entropy it is found that the system is thermodynamically stable up to 1200 K. The imaginary part of the calculated dielectric function ε₂(ω) could reproduce the six prominent peaks which are observed in experiment. From the calculated ε(ω), other optical properties such as refractive index, reflectivity and electron energy-loss spectrum are obtained up to the photon energy range of 30 eV.     

Structural,elastic, electronic and thermal properties of the cubic perovskite-type BaSnO3

First-principles calculations are performed to investigate the structural, elastic, electronic and thermal properties of the cubic perovskite-type BaSnO₃. The ground-state properties are in agreement with experimental data. The independent elastic constants, C₁₁, C₁₂ and C₄₄, are calculated from direct computation of stresses generated by small strains. A linear pressure dependence of the elastic stiffnesses is found. From the theoretical elastic constants, we have computed the elastic wave velocities along [100], [110] and [111] directions. The shear modulus, Young's modulus, Poisson's ratio, Lamé’s coefficients, average sound velocity and Debye temperature are estimated in the framework of the Voigt-Reuss-Hill approximation for ideal polycrystalline BaSnO₃ aggregate. Using the sX-LDA for the exchange-correlation potential, the calculated indirect fundamental band gap value is in very good agreement with the measured one. The analysis of the site-projected l-decomposed density of states, charge transfer and charge density shows that the bonding is of ionic nature. Through the quasi-harmonic Debye model, in which the phononic effects are considered, the temperature effect on the lattice constant, bulk modulus, thermal expansion coefficient, heat capacity and Debye temperature is calculated.     

Electro-structural correlations,elastic and optical properties among the nanolaminated ternary carbides Zr2AC

We have performed ab initio calculations for the nanolaminates Zr₂AC (A = Ti, In, Tl, Si, Ge, Sn, Pb, P, As, S) ceramics to study their electronic structure, elastic and optical properties. In this work, we used the accurate augmented plane wave plus local orbital method with density functional theory to find the equilibrium structural parameters, dielectric functions and to compute the full elastic tensors. The obtained elastic constants were used to quantify the stiffness of the Zr₂AC phases and to appraise their mechanical stability. The relationship between elastic, electronic and valence electron concentration is discussed. Our results show that the bulk modulus and shear modulus increase across the periodic table for Zr₂AC. Furthermore, trends in elastic stiffness are well explained in terms of electronic structure analysis, as occupation of valence electrons in states near the Fermi level of Zr₂AC. We show that increments of bulk moduli originate from additional valence electrons filling states involving Zr d–A p. We show also that Zr d–A p hybridizations are located just below the Fermi level and are weaker bonds than the Zr d–C p hybridizations, which are deeper in energy. As a function of the p-state filling of the A element the Zr d–A p bands are driven to deeper energy. The optical spectra were analyzed by means of the electronic structure, which provides theoretical understanding of the conduction mechanism of these ceramics.     

Electronic,elastic and thermal properties of lutetium intermetallic compounds

The electronic, structural, elastic, thermal and mechanical properties of Lutetium intermetallic compounds LuX (X = Mg, Cu, Ag, Au, Zn, Cd and Hg) have been studied using ab-initio full potential linear augmented plane wave (FP-LAPW) with the generalized gradient approximation (GGA) in their non magnetic phase. The ground state properties such as lattice constant, bulk modulus, pressure derivatives of bulk modulus are reported in CsCl-(B₂ phase) structure. We also report the band structure and density of states at equilibrium lattice constant. The calculated band structures indicate that these intermetallics are metallic in nature. The second order elastic constants of these compounds are also predicted for the first time. The ductility of these compounds is determined by calculating the bulk to shear ratio B/G_H.     

Theoretical assessment of structural,mechanical, and thermodynamic properties of Pd2Al

The physical properties, namely structural, mechanical, and thermodynamic properties, of Pd₂Al intermetallic compound were explored through first-principles calculations within the framework of density functional theory. The calculated lattice constants were consistent with the available experimental data. The calculated elastic constants revealed that Pd₂Al was mechanically stable. By the predicted elastic constants, several related properties, namely Cauchy pressures, shear anisotropy factors, directional Young's modulus, bulk, shear and Young's moduli, the ratio of K/G, Vickers hardness, sound velocity, and minimum thermal conductivity for Pd₂Al were evaluated. According to the calculated results, it was found that Pd₂Al possesses a highly anisotropic feature and behaves in a ductile manner with low stiffness. Finally, temperature-dependence of thermodynamic properties, namely Debye temperature and heat capacity, were also evaluated through the quasi-harmonic Debye model.     

Structural,mechanical, electronic,optical properties and effective masses of CuMO2 (M = Sc,Y, La) compounds: First-principles calculations

The structural, elastic, mechanical, electronic, optical properties and effective masses of CuM_IIIBO₂ (M_IIIB = Sc, Y, La) compounds have been investigated by the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory under local density approximation. The equilibrium structural parameters are in good agreement with previous experimental and theoretical data. To our knowledge, there are no available data of elastic constants for comparison. The bulk, shear and Young's modulus, ratio of B/G, Poisson's ratio and Lamé's constants of CuM_IIIBO₂ have been studied. The electronic structures of CuM_IIIBO₂ are consistent with other calculations. The population analysis, charge densities and effective masses have been shown and analyzed. The imaginary and real parts of the dielectric function, refractive index and extinction coefficient of CuM_IIIBO₂ are calculated. The interband transitions to absorption of CuM_IIIBO₂ have been analyzed.     

First principles study of structural,electronic, elastic and thermal properties of YX (X = Cd,In, Au,Hg and Tl) intermetallics

The structural, electronic, elastic and thermal properties of YX (X = Cd, In, Au, Hg and Tl) intermetallic compounds crystallizing in B₂-type structure have been studied using first principles density functional theory within generalized gradient approximation (GGA) for the exchange correlation potential. Amongst all the YX compounds, YIn is stable in distorted tetragonal (P4/mmm) CuAu-type structure at ambient pressure with very small energy difference of 0.00681 Ry. but it undergoes to CsCl-type (B₂ phase) structure at 23.3 GPa. Rest of the compounds are stable in B₂ structure at ambient condition. The values of elastic moduli as a function of pressure are also reported. The ductility of these compounds has been analyzed using the Pugh rule. Our calculated results indicate that YTl is the most ductile amongst all the B₂-YX compounds. YAu is the hardest and less compressible compound due to the largest bulk modulus. The elastic properties such as Young's modulus (E), Poisson's ratio (σ) and anisotropic ratio (A) are also predicted. The anisotropic factor is found to be unity for YHg which shows that this compound is isotropic.     

Theoretical investigation of the structural,elastic, electronic and optical properties of the ternary indium sulfide layered structures AInS2 (A = K,Rb and Cs)

Ab initio calculations were performed to investigate the structural, elastic, electronic and optical properties of the ternary layered systems AInS₂ (A = K, Rb and Cs). The calculated structural parameters are in good agreement with the existing experimental data. Analysis of the electronic band structure shows that the three studied materials are direct band-gap semiconductors. Density of states, charge transfers and charge density distribution maps were computed and analyzed. Numerical estimations of the elastic moduli and their related properties for single-crystal and polycrystalline aggregates were predicted. The optical properties were calculated for incident radiation polarized along the [100], [010] and [001] crystallographic directions. The studied materials exhibit a noticeable anisotropic behaviour in the elastic and optical properties, which is expected due to the symmetry and the layered nature of these compounds.     

First-principles study of structural,elastic, electronic and vibrational properties of BiCoO3

We used density functional theory (DFT) to study the structural, elastic, electronic, and lattice dynamical properties of tetragonal BiCoO₃ applying the “norm-conserving” pseudopotentials within the local spin density approximation (LSDA). The calculated equilibrium lattice parameters and atomic displacements are in agreement with the available experimental and theoretical results. Moreover, the structural stability of tetragonal BiCoO₃ were confirmed by the calculated elastic constants. In addition, the elastic properties of polycrystalline aggregates including bulk, shear and Young's moduli, and Poisson's ratio are also determined. The electronic band structure, total and partial density of states (DOS and PDOS) with ferromagnetic spin configuration are obtained. The results show that tetragonal BiCoO₃ has an indirect band gap with both up- and down-spin configurations and its bonding behavior is of covalent nature. We compute Born effective charge (BEC) which is found to be quite anisotropic of Bi, Co and O atoms. The infrared and Raman active phonon mode frequencies at the Г point are found. The phonon dispersion curves exhibit imaginary frequencies which lead from the high-symmetry tetragonal phase to low-symmetry rhombohedral phase in BiCoO₃. The six independent elastic constants, including bulk, shear and Young's moduli, and Poisson's ratio, complete BEC tensor and phonon dispersion relations in tetragonal BiCoO₃ are predicted for the first time. Results of the calculations are compared with the existing experimental and theoretical data.     

First-principles calculations of the stability and hydrogen storage behavior of C14 Laves phase compound TiCrMn

The structural, elastic properties, electronic structure and hydrogen storage behavior of TiCrMn with a hexagonal C14 structure were investigated by the first-principles calculations within the frame work of DFT. The calculated lattice constants were consistent with the experimental values, and obtained cohesive energy and formation enthalpy showed TiCrMn is of the structural stability. These results also indicated that Mn atoms would optionally substitute on the Cr sites of TiCr₂ phase to form the ternary intermetallic TiCrMn. The five independent elastic constants as well as polycrystalline elastic parameters (bulk modulus B, shear modulus G, Young's modulus E, Poisson's ratio ν and anisotropy value A) were calculated, and then the ductility and elastic anisotropy of TiCrMn were discussed in details. Furthermore, the electronic DOS and charge density distribution of TiCrMn were also calculated, which revealed the underlying mechanism of structural stability and chemical bonding. Finally, the binding energy of hydrogen in hydride TiCrMn(H₃) was investigated, confirming the better hydrogen storage behavior of C14 Laves phase TiCrMn.     

Structural,elastic and electronic properties of β′ phase precipitate in Mg–Gd alloy system investigated via first-principles calculation

The β′ phase precipitate in Mg–Gd alloy system has been investigated by means of first-principles calculation within the generalized gradient approximation. The lattice parameters are determined theoretically by structural optimization of full relaxation, and the Mg₇Gd is found to be energetically more stable compared with the Mg₁₅Gd from the calculated formation energy. The nine independent elastic constants are calculated, indicating the proposed Mg₁₅Gd structure in literature is mechanically unstable. Then the polycrystalline bulk modulus B, Young's modulus E, shear modulus G, Poisson ratio ν of Mg₇Gd are gained by the Voigt–Reuss–Hill (VRH) approximation. The ductility and plasticity, especially elastic anisotropy are discussed in details. Based on the electronic density of states and charge density distribution, the covalent bonding and metallic bonding are exhibited in Mg₇Gd compound. Last, the Debye temperature is also calculated for the investigation in the future.     

Structural,electronic, elastic,thermodynamic and vibration properties of TbN compound from first principles calculations

We have predicted structural, electronic, elastic, thermodynamic and vibration characteristics of TbN, using density functional theory within generalized-gradient (GGA) apraximation. For the total energy calculation we have used the projected augmented plane-wave (PAW) implementation of the Vienna Ab initio Simulation Package (VASP). We have used to examine structure parameter in eight different structures such as in NaCl (B1), CsCl (B2), ZB (B3), Tetragonal (L1₀), WC (Bh), NiAs (B8), PbO (B10) and Wurtzite (B4). We have performed the thermodynamics properties for TbN by using quasi-harmonic Debye model. We have, also, predicted the temperature and pressure variation of the volume, bulk modulus, thermal expansion coefficient, heat capacities and Debye temperatures in a wide pressure (0–130 GPa) and temperature ranges (0–2000 K). Furthermore, the band structure, phonon dispersion curves and corresponding density of states are computed. Our results are compared to other theoretical and experimental works, and excellent agreement is obtained.     

Elastic properties and electronic structures of typical Al–Ce structures from first-principles calculations

The elastic property and electronic structure of three typical Al–Ce structures have been studied by means of first-principles calculations within GGA approximation. The optimized structural parameters for these precipitates agree very well with experimental data. The obtained negative cohesive energy and formation enthalpy show that all of these precipitates have strong structural stability. Elastic constants as well as other mechanical parameters such as bulk modulus B, shear modulus G, Young’s modulus E and Poisson’s ratio ν for these phases are computed and discussed. The calculated electronic densities of state and charge distribution show the covalent features of Ce–Ce and Al–Ce bonding in three phases, which reveals the underlying mechanism for the elastic properties of these Al–Ce structures.     

First-principles investigation of the binary AB2 type Laves phase in Mg–Al–Ca alloy: Electronic structure and elastic properties

First-principles calculations have been carried out to investigate the electronic structure and mechanical properties of the main binary Laves phase CaMg₂, CaAl₂ and MgAl₂ with C14, C15 and C36 structures in Mg–Al–Ca alloy, respectively. The optimized structural parameters were in very good agreement with the experimental values. The calculated heat of formation and cohesive energy showed that the C15-CaAl₂ Laves phase was of the strongest alloying ability and structural stability. The electronic density of states (DOS) and charge density distribution were given. The elastic parameters C_ij were calculated, then the bulk modulus, shear modulus, Young's modulus, Possion's ratio and anisotropy value were derived. The ductility and plasticity were discussed in comparison with the previous experimental and theoretical data. The results showed that C14-MgAl₂ is of the best ductility and C15-MgAl₂ is of the best plasticity in the investigated binary alloys.     

Ab initio Predictions of Structural and Thermodynamic Properties of Zr2AlC Under High Pressure and High Temperature

The structural and thermodynamic properties of Zr₂AlC at high pressure and high temperature are investigated by first principles density functional theory method. The calculated lattice parameters of Zr₂AlC are in good agreement with the available theoretical data. The pressure dependences of the elastic constants, bulk modulus, shear modulus, Young's modulus, and Vickers hardness of Zr₂AlC are successfully obtained. The elastic anisotropy is examined through the computation of the direction dependence of Young's modulus. By using the quasiharmonic Debye model, the thermodynamic properties including the Debye temperature, heat capacity, volume thermal expansion coefficient, and Grüneisen parameter at high pressure and temperature are predicted for the first time.