Calculated Equilibrium Lattice Parameters Research Articles

Phase stability and elastic properties of Al–Pr intermetallic compounds from first principles calculations

To develop a better understanding of the phase stability and elastic properties of the Al–Pr intermetallic compounds, the lattice parameters, enthalpy of formation, and cohesive energy and elastic modulus of the Al–Pr intermetallic compounds were investigated by using first-principles calculations based on density functional theory. The calculated equilibrium lattice parameters are by available experimental values. The thermodynamic properties were discussed and analyzed with an energy minimum approach in terms of structural stability. The results reveal that the Al2Pr intermetallic compound has the strongest alloying ability. α-AlPr intermetallic compounds show a minimum of cohesive energy. The results of the elastic modulus calculation show that the intermetallic compound α-AlPr3 behaves with the biggest anisotropy, and the intermetallic compound Al2Pr tends to be isotropic.

Electronic, mechanical, optical and thermodynamic properties of the quaternary semiconductors Sr3GeMgN4 and Ba3GeMgN4

The electronic structure, optical and thermodynamic properties of M3GeMgN4 (M = Sr or Ba) nitrides have been investigated using first-principles calculations. The calculated equilibrium lattice parameters and inter-atomic bond-lengths show excellent concordance with experiment. The elastic constants (Cijs) and their derived properties have been calculated showing that the examined compounds are mechanically stable and elastically soft, ductile and anisotropic. The analysis of the electronic structure reveals a semiconductor comportment for both crystals. The Sr3GeMgN4 (Ba3GeMgN4) compound possesses a direct (indirect) energy gap of 1.476 eV (1.194 eV). The chemical bonding in both semiconductors is dominated by a covalent character, which originates from the Ge-N and Mg-N hybridized states. Both nitrides show moderate dielectric properties, high visible and UV absorbance, indicating that both materials are suitable for optoelectronic applications. Phononic dispersion curves have demonstrated the dynamical stability of the studied crystals.

A first-principles study of the electronic, mechanical, vibrational, and optical properties of the zirconium carbide under high pressure

Zirconium carbide is a compound widely used in cutting tools, nuclear reactors, field emitter arrays and solar energy receivers; additionally, combined with other materials, it can be used in rocket technology and the aerospace industry. For this work was studied the effect of the high hydrostatic pressure on the electronic, mechanical, vibrational, and optical properties of the ZrC, from first principles calculations based on the Density Functional Theory. The calculated enthalpy and cohesive energy data show a B1 (NaCl) to B2 (CsCl) phase transition at 297 GPa. For the B1 phase, results for the calculated equilibrium lattice parameters, bands structure, electron and phonon densities of states, elastic moduli constants, entropy, enthalpy, Gibbs free energy, heat capacity, reflectivity, loss function, conductivity, and dielectric function are consistent with the available experimental and theoretical data. Our results for phonons show that the B1 phase is dynamically stable; in contrast, the B2 phase is not stable. Furthermore, when pressure is applied, the calculated density of electronic states shows that the C 2p-orbitals around the Fermi energy contribute significantly to the conduction band, turning the compound into a ductile the material, with a mixture of metallic and ionic-covalent bonds. On the other hand, the study of the mechanical properties of the B1 phase shows a highest mechanical resistance and maximum thermal absorption, above 356 K and 638 K, respectively; but these switch to higher temperatures as pressure is applied. Finally, the B1 phase of the ZrC is a good coating material and a photon detector at low frequencies in the UV region, but also at the visible and infrared regions; although, increasing the pressure, the values of the optical properties increase. The increase of the parameters’ values of the studied properties, as the pressure increases, indicates that the ZrC could be more efficient in a wider range of applications.

Physical properties of BaRu2X2 (X = P, As) superconducting compound sunder pressure effects: Ab initio study

We report the results of a detailed ab initio investigation of the pressure effects up to 18 GPa on the structural, elastic and thermodynamic properties of the superconducting compounds BaRu2P2 and BaRu2As2. The exchange-correlation effects were modeled through the PBEsol version of the generalized gradient approximation. The calculated equilibrium lattice parameters are in good agreement with the available experimental counterparts. The lattice parameter c decreases with increasing pressure faster than the lattice parameter a. The computed single-crystal elastic constants (Cij) show that both BaRu2P2 and BaRu2As2 are mechanically stable under pressure effect up to 18 GPa. Pressure dependence of the single-crystal and polycrystalline elastic moduli, and related physical parameters, namely Cij, Young's modulus, shear modulus, bulk modulus, Poisson's ratio, average sound velocity, Debye temperature (θD), minimum thermal conductivity (Kmin), melting temperature (Tm) and Vickers hardness (HV), were successfully calculated for the pressure range 0-18 GPa. The quasi-harmonic Debye model was successfully used to explore the temperature and pressure dependencies of the unit cell volume, bulk modulus, isochoric and isobar heat capacities, volume thermal expansion coefficient and Debye temperature. The good agreement between the results obtained using the quasi-harmonic Debye model and those corresponding deduced from the elastic constants constitutes proof of the reliability of the results obtained.

Structural, elastic, electronic and optical properties of the half-Heusler ScPtSb and YPtSb compounds under pressure

First-principles calculations using the plane-wave pseudopotential method within the generalized gradient approximation method were performed to study the pressure dependence of the structural, elastic, electronic and optical properties for the half-Heusler compounds ScPtSb and YPtSb in a cubic MgAgAs-type structure. The calculations were performed with the inclusion of spin-orbit coupling. The calculated equilibrium lattice parameters are in good agreement with the available experimental and theoretical values. The crystal rigidity and mechanical stability were discussed using the elastic constants and related parameters, namely bulk modulus, shear modulus, Debye temperature, Poisson's coefficient, Young's modulus and isotropic sound velocities. The calculated electronic band structures show that ScPtSb has an indirect gap of Γ-X type, whereas YPtSb has a direct band gap of Γ-Γ type. Furthermore, the effect of pressure on the optical properties, namely the dielectric function, absorption spectrum, refractive index, extinction coefficient, reflectivity and energy-loss spectrum is investigated for both compounds ScPtSb and YPtSb.

First-principles calculations of structural, elastic and electronic properties of (TaNb)0.67(HfZrTi)0.33 high-entropy alloy under high pressure

To clarify the effect of pressure on a (TaNb)0.67(HfZrTi)0.33 alloy composed of a solid solution with a single body-centered-cubic crystal structure, we used first-principles calculations to theoretically investigate the structural, elastic, and electronic properties of this alloy at different pressures. The results show that the calculated equilibrium lattice parameters are consistent with the experimental results, and that the normalized structural parameters of lattice constants and volume decrease whereas the total enthalpy difference ΔE and elastic constants increase with increasing pressure. The (TaNb)0.67(HfZrTi)0.33 alloy exhibits mechanical stability at high pressures lower than 400 GPa. At high pressure, the bulk modulus B shows larger values than the shear modulus G, and the alloy exhibits an obvious anisotropic feature at pressures ranging from 30 to 70 GPa. Our analysis of the electronic structures reveals that the atomic orbitals are occupied by the electrons change due to the compression of the crystal lattices under the effect of high pressure, which results in a decrease in the total density of states and a wider electron energy level. This factor is favorable for zero resistance.

DFT COMPUTATION OF THE BAND STRUCTURE AND DENSITY OF STATE FOR ZnO HALITE STRUCTURE USING FHI-aims CODE.

This research work is on Density Functional Theory (DFT) within Local Density Approximation as parameterised by Perdew and Wang (pw-lda).The calculation was performed using Fritz Haber Institute Ab-initio Molecular Simulations (FHI-aims) code based on numerical atomic-centered orbital basis sets. The electronic band structure, density of state (DOS) and band gap energy were calculated for ZnO compound. The band structure and Density of States (DOS) diagrams are plotted from the calculated equilibrium lattice parameters. The experimentally lattice constant values were used to calculate the minimum total energy. The calculated electronic band structure results show that ZnO (Halite) is an indirect semiconductor with energy band gap of 0.89 eV. Hence, the HOMO is -0.863382 eV at L_symmetry point and LUMO is 0.0239417 eV at ᴦ- point. The DOS energy level within the compound shows considerable high state of electron occupation and the DOS observed around the Fermi level at zero level indicate that it has conducting properties. In general, FHI-aims code has shown better accuracy and prediction of band structure calculation within reasonable computational methods.

Elastic and mechanical properties of hydroxyapatite under pressure: A first-principles investigation

The structural, elastic, and mechanical properties of hydroxyapatite (HAp) were investigated by generalized gradient approximation (GGA) in the functional form by Perdew, Bruke, and Ernzerhof (PBE) exchange-correlation functional using density-functional theory. Our calculated equilibrium lattice parameters at ambient pressure are in good agreement with the experimental and previous theoretical results. The details of the structural, mechanical, and electrical properties such as elastic constants, bulk modulus B, shear modulus G, Young’s modulus E, Poisson’s ratioν, Cauchy pressure, shear anisotropic factor A, and total density of states under pressure ranging 0 GPa to 10 GPa are studied. The lattice parameters a and c are found to be decreased with increasing pressure. Moreover, the lattice parameter a is more sensitive to external pressure than c. The calculated elastic constants of hexagonal HAp increase with increasing pressure. The elastic constants C11 and C33, which represent the elasticity in length are larger than the elasticity in shape, which represent by the elastic constants C12, C13, C44, and C66. The deformation resistances along the axial direction are stronger than the deformation resistances in shape. The calculated B/G, Poisson’s ratio ν, and Cauchy pressure show that the hexagonal HAp behaves as a ductility material at ambient pressure and has more ductile under pressure. While the calculated shear anisotropic factor A indicate that the HAp shows elastic anisotropy under pressure. Moreover, calculated total density of states (DOS) show that HAp becomes more insulator property with increasing pressure.

First-principles investigation of the structural, electronic, magnetic, thermodynamic and optical properties of the cubic Sr1-xMnxS ternary alloys

This article reports the structural, electronic, magnetic, thermodynamic and optical properties of the Sr1-xMnxS ternary alloys, this type of research is useful for discovering a new efficient material suitable for spintronic. The systematic calculations were performed using density functional theory under the framework of the full potential linearized augmented plane wave (FP-LAPW). It is verified that all the investigated systems are in a stable ferromagnetic phase in comparison to the other magnetic structures. The optimized structural properties reveal that the calculated equilibrium lattice parameters decrease with the increase of the concentration of Mn elements, and some other features were computed too, such as the bulk modulus (B) and its pressure derivatives (B′). The study revealed important prediction about the spin polarized band structure and electronic density of state calculations for Sr1-xMnxS that exhibit semiconducting nature. In addition, the analysis of the magnetic properties of Sr1-xMnxS alloys shows that the value of the total magnetic moment equal to 5μB per Mn atom. Moreover, the thermodynamic properties are studied and investigated using the quasi-harmonic model. Finally, the optical properties are described by calculating the absorption coefficients, dielectric function along with real and imaginary part of the dielectric function.

First-principles predictions of anisotropies in elasticity and sound velocities of CsCl-type refractory intermetallics: TiTM, ZrTM and HfTM (TM = Fe, Ru, Os)

ABSTRACTStructural properties, elastic properties, sound velocities and Debye temperatures of CsCl-type refractory TiTM, ZrTM and HfTM (TM = Fe, Ru, Os) intermetallics were investigated using first-principles calculations. The calculated equilibrium lattice parameters are coincided with the reported experimental and theoretical data. Based on single-crystal elastic constants, polycrystalline elastic moduli, Poisson’s ratios, sound velocities and Debye temperatures were evaluated. Anisotropies in elastic moduli of these CsCl-type intermetallics were discussed by elastic anisotropy indexes, three-dimensional surface constructions and their projections, and directional elastic modulus. The results showed that ZrFe has the highest elastic anisotropy and ZrOs presents the lowest one. Finally, sound velocities, Debye temperatures and their anisotropies were also calculated and discussed.

DFT based study on structural stability and transport properties of Sr3AsN: A potential thermoelectric material

Abstract

Implications of Oxygen–Sulfur Exchange on Structural, Electronic Properties, and Stability of Alkali‐Metal Hexatitanates

The structural and electronic properties and thermal stability of a new series of sulfur‐containing compounds (A2Ti6S13 [A = Li+, Na+, or K+]) are studied using density functional theory (DFT). The calculated equilibrium lattice parameters are larger compared to their oxide counterparts, Li2Ti6O13, Na2Ti6O13, and K2Ti6O13. These new compounds are thermodynamically stable with standard molar formation enthalpies of −8743, −8389, and −8386 kJ mol−1, and a cell voltage per A+ insertion/desertion process of roughly 2 V, which is comparable with the oxygen‐based systems. The electronic band structures of these systems indicate a semiconductor‐to‐metallic transition, where the metallic character is more accentuated for K2Ti6S13 and Li2Ti6S13.

Properties of BiMnO3 and BiMn0.5Nb0.5O3 from ab initio simulations

Ab initio studies of structural and electronic properties of the monoclinic perovskite-type BiMnO3 and BiMn0.5Nb0.5O3 crystals are presented using the pseudo-potential plane wave method within the density functional theory in generalized – gradient approximation. The calculated equilibrium lattice parameters remain in a good agreement with the available experimental data. The gap energy took values in the range Eg=0.2−0.5eV for both compounds.

Electron-phonon interaction in the binary superconductor lutetium carbide LuC2 via first-principles calculations

Structural, electronic, electron-phonon coupling and superconducting properties of the intermetallic compound LuC2 are investigated by means of ab initio pseudopotential plane wave method within the generalized gradient approximation. The calculated equilibrium lattice parameters yielded a very good accord with experiment. There is no imaginary phonon frequency in the whole Brillouin zone supporting thus the dynamical stability in the material of interest. The average electron-phonon coupling parameter is found to be 0.59 indicating thus a weak-coupling BCS superconductor. Using a reasonable value of μ* = 0.12 for the effective Coulomb repulsion parameter, the superconducting critical temperature Tc is found to be 3.324 which is in excellent agreement with the experimental value of 3.33 K. The effect of the spin-orbit coupling on the superconducting properties of the material of interest has been examined and found to be weak.

First-principles investigations on structural, elastic, electronic properties and Debye temperature of orthorhombic Ni3Ta under pressure

ABSTRACT The structural, elastic, electronic properties and Debye temperature of Ni3Ta under different pressures are investigated using the first-principles method based on density functional theory. Our calculated equilibrium lattice parameters at 0 GPa well agree with the experimental and previous theoretical results. The calculated negative formation enthalpies and elastic constants both indicate that Ni3Ta is stable under different pressures. The bulk modulus B, shear modulus G, Young’s modulus E and Poisson’s ratio ν are calculated by the Voigt–Reuss–Hill method. The bigger ratio of B/G indicates Ni3Ta is ductile and the pressure can improve the ductility of Ni3Ta. In addition, the results of density of states and the charge density difference show that the stability of Ni3Ta is improved by the increasing pressure. The Debye temperature Θ D calculated from elastic modulus increases along with the pressure.

Structural Stability, Electronic and Magnetic Properties of (Ni1−xCox)2MnSn Quaternary Heusler Alloys

In this study, we present the calculated structural, electronic and magnetic properties of mixed Heusler alloys (Ni[Formula: see text]Co[Formula: see text]MnSn. Using ab initio calculations with the full-potential augmented plane-wave method (FP-LAPW), we evaluated the various possible configurations of Ni and Co sites in the (Ni[Formula: see text]Co[Formula: see text]MnSn crystallographic lattice. The lowest energy configuration is determined based on energetic considerations. The calculated equilibrium lattice parameters and magnetic moments are in a reasonable agreement with available experimental data. Of interest, we found that the change of total magnetic moment can be interpreted as a linear variation of the magnetic moment of manganese and cobalt atoms.

Structural, elastic and lattice dynamical properties of the alkali metal tellurides: First-principles study

We report a detailed first-principles density functional calculations to understand the systematic trends for crystal structure, elastic and lattice dynamical properties of the anti-fluorite alkali metal tellurides M2Te depending from the type of the M cations (M are Li, Na, K and Rb). The calculated equilibrium lattice parameters are in very good agreement with the available experimental data. Single-crystal and polycrystalline elastic moduli and their related properties of the title compounds were calculated via the stress-strain method. The relatively weak values of the calculated elastic moduli demonstrate the weak resistance of these compounds to applied external forces. Phonon dispersion curves throughout the Brillouin zone and corresponding density of states were calculated using the linear response approach. No imaginary phonon modes were found, which indicate the dynamical stability of the examined materials. The atomic displacements at Γ point were determined. Low-frequency dielectric properties and infrared response were investigated.

Electronic structures and thermodynamic properties of HfAl3 in L12, D022 and D023 structures

To better understand the relative stability and bonding characteristics of the L12, D022 and D023 structures for HfAl3, the formation enthalpies, electronic structures and thermodynamics properties were investigated by first-principles calculations. The agreement of calculated equilibrium lattice parameters and formation enthalpies with experimental results indicates the reliability of this work. The order of structural stability is D023>D022>L12. The results of densities of states, atomic Mulliken charge and bond population support the best structural stability for D023 structure. Variations of thermodynamic properties with temperature were predicted via phonon frequencies calculation. The enthalpy, entropy, free energy of D023 structure change more quickly than those of the other two structures. The Debye temperatures of L12, D022 and D023 structures are 399, 407 and 416 K, respectively. The volume thermal expansions for HfAl3 increase exponentially at the low temperature, whereas the thermal expansion coefficients increase linearly at the high temperature.

Effects of pressure on anisotropic elastic properties and minimum thermal conductivity of D022-Ni3Nb phase: First-principles calculations

The elastic constants, formation enthalpies, elastic moduli, Poisson's ratios, acoustic velocities and Debye temperatures of D022-Ni3Nb phase at different pressures are determined using first-principles calculations. The effects of pressure on anisotropic elastic properties and minimum thermal conductivity are discussed in detail. It is found that the calculated equilibrium lattice parameters at 0 GPa well agree with the experimental results. The negative formation enthalpy indicates that Ni3Nb phase is thermodynamically stable in the ground state, and the stability becomes better as the pressure is increased. The bigger ratio of B/G (larger than 1.75) and positive Cauchy pressure indicate that Ni3Nb phase is ductile. Moreover, Ni3Nb phase exhibits high elastic anisotropy, and the elastic anisotropies become increasingly pronounced with the increase of pressure. Additionally, the anisotropic chemical bonds of Ni3Nb phase reduce the minimum thermal conductivity. The minimum thermal conductivity increases with the increased pressure.

Elastic and Thermal Properties of Silicon Compounds from First-Principles Calculations

Abstract The structural and elastic properties of V-Si (V3Si, VSi2, V5Si3, and V6Si5) compounds are studied by using first-principles method. The calculated equilibrium lattice parameters and formation enthalpy are in good agreement with the available experimental data and other theoretical results. The calculated results indicate that the V-Si compounds are mechanically stable. Elastic properties including bulk modulus, shear modulus, Young’s modulus, and Poisson’s ratio are also obtained. The elastic anisotropies of V-Si compounds are investigated via the three-dimensional (3D) figures of directional dependences of reciprocals of Young’s modulus. Finally, based on the quasi-harmonic Debye model, the internal energy, Helmholtz free energy, entropy, heat capacity, thermal expansion coefficient, Grüneisen parameter, and Debye temperature of V-Si compounds have been calculated.