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.     

The disproportionation reaction phase transition,mechanical, and lattice dynamical properties of the lanthanum dihydrides under high pressure: A first principles study

The pressure-induced disproportionation reaction phase transition, mechanical, and dynamical properties of LaH₂ with fluorite structure under high pressure are investigated by performing first-principles calculations using the projector augmented wave (PAW) method. The phase transition of 2LaH₂ → LaH + LaH₃ obtained from the usual condition of equal enthalpies occurs at the pressure of 10.38 GPa for Perdew–Wang (PW91) functional and 6.05 GPa for Ceperly–Adler (CA) functional, respectively. The result shows that the PW91 functional calculations agree excellently with the experimental finding of 11 GPa of synchrotron radiation (SR) X-ray diffraction (XRD) of Machida et al. and 10 GPa of their PBE functional theoretical result. Three independent single-crystal elastic constants, polycrystalline bulk modulus, shear modulus, Young's modulus, elastic anisotropy, Poisson's ratio, the brittle/ductile characteristics and elastic wave velocities over different directions dependences on pressure are also successfully obtained. Especially, the phonon dispersion curves and corresponding phonon density of states of LaH₂ under high pressure are determined systematically using a linear-response approach to density functional perturbation theory (DFPT). Our results demonstrate that LaH₂ in fluorite phase can be stable energetically up to 10.38 GPa, stabilized mechanically up to 17.98 GPa, and stabilized dynamically up to 29 GPa, so it may remain a metastable phase above 10.38 GPa up to 29 GPa, these calculated results accord with the recent X-Ray diffraction experimental finding and theoretical predictions of Machida et al.     

Structural, electronic, bonding, and elastic properties of NH3BH3: a density functional study

The structural, electronic, bonding, and elastic properties of the low-temperature orthorhombic phase of NH(3)BH(3) are studied by means of first-principles total energy calculations based on the pseudopotential method. The calculated structural parameters of NH(3)BH(3) are found to be in good agreement with the experimental values. From the band structure calculations, the compound is found to be an indirect bandgap insulator with the bandgap of 5.65 eV (5.90 eV) with LDA(GGA) along the Γ-Z direction. The Mulliken bond population and the charge density distributions are used to analyze the chemical bonding in NH(3)BH(3) . The study reveals that B-H bonds are more covalent than N-H bonds. The elastic constants are predicted for ambient as well as pressures up to 6 GPa, from which theoretical values of all the related mechanical properties such as bulk modulus, shear modulus, Young's modulus, Poisson's ratio, and anisotropy factors are calculated. It is found that NH(3)BH(3) is mechanically stable at ambient and also external pressures up to 6 GPa. As pressure increases all the calculated elastic moduli of NH(3)BH(3) increase, indicating that the compound becomes more stiffer and hard under pressure. From the ratio of shear modulus to bulk modulus (G/B), we conclude NH(3)BH(3) to be ductile in nature, and the ductility increases with pressure. The present results confirm the experimentally observed less plastic nature of the low-temperature phase of NH(3)BH(3) .     

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, electronic and elastic properties of MAX phases M2GaN (M = Ti, V and Cr)

Based on first-principles total energy calculations, we have investigated the systematic trends for structural, electronic and elastic properties of the MAX phases M₂GaN depending on the type of M transition metal (M are Ti, V and Cr). The optimized zero pressure geometrical parameters: the two unit cell lengths (a, c), the internal coordinate z and the bulk modulus are calculated. The results for the lattice constants are in agreement with the available experimental data. The band structures show that all studied materials are electrical conductors. The analysis of the site-projected l-decomposed density of states shows that bonding is due to M d-N p and M d-Ga 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 10.5–11.0. The isotropic elastic moduli, namely, bulk modulus (B), shear modulus (G), Young's modulus (E) and Poisson's ratio (σ) are calculated in framework of the Voigt–Reuss–Hill approximation for ideal polycrystalline M₂GaN aggregates. We estimated the Debye temperature of M₂GaN from the average sound velocity. This is the first quantitative theoretical prediction of the electronic structures, and elastic constants and related properties for Ti₂GaN, V₂GaN and Cr₂GaN compounds that require experimental confirmation.     

Theoretical prediction of the structural,elastic, electronic,optical and thermal properties of the cubic perovskites CsXF3 (X = Ca,Sr and Hg) under pressure effect

Some physical properties of the cubic perovskites CsXF₃ (X = Ca, Sr and Hg) have been investigated using pseudopotential plane-wave method based on the density functional theory. The calculated lattice parameters within GGA and LDA agree reasonably with the available experimental data. The elastic constants and their pressure derivatives are predicted using the static finite strain technique. We derived the bulk and shear moduli, Young's modulus, Poisson's ratio and Lamé’s constants for ideal polycrystalline aggregates. The analysis of B/G ratio indicates that CsXF₃ (X = Ca, Sr and Hg) are ductile materials. The thermal effect on the volume, bulk modulus, heat capacity and Debye temperature was predicted.     

Elastic, electronic and thermal properties of YSZ from first principles

First principles calculations were performed to investigate the elastic, electronic and thermal properties of 14% cubic yttria-stabilized zirconia (YSZ) using the pseudo potential plane-wave method within the gradient generalized approximation (GGA) for the exchange and correlation potential. Computed lattice constant parameters are in good agreement with the available experimental results. The three independent elastic constants were computed by means of the stress-strain method, indicating that 14% cubic YSZ is a mechanically stable structure. From the knowledge of the elastic constants, a set of related properties, namely bulk, shear modulus, Young’s modulus, sound velocity, Debye temperature, thermal capacity and minimum thermal conductivity are numerically estimated in the frame work of the Voigt-Reuss-Hill approximation for YSZ polycrystalline. The calculated bulk modulus, shear modulus, Young’s modulus, sound velocity, Debye temperature, thermal capacity and minimum thermal conductivity are in reasonable agreement with the available experimental and theory data. Density of states, charge density and Mulliken population analysis show that the 14% cubic YSZ is covalent and possess ionic character.     

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.     

First-principles investigation of the ternary scandium based inverse-perovskite carbides Sc3AC (A = Al,Ga, In and Tl)

Based on first-principles approach, we present a comparative study of structural, electronic, elastic and thermo-dynamical properties of the series of inverse-perovskites Sc₃AC, with A = Al, Ga, In and Tl. The calculated equilibrium lattice constants are in excellent agreement with the experimental and available theoretical data. The electronic band structures and densities of states profiles show that the studied compounds are conductors. Analysis of atomic site projected local density of states and charge densities reveals that a mixture of covalent–ionic–metallic characterizes the chemical bonding of the considered inverse-perovskites. Pressure dependence up to 40 GPa of the single-crystal and polycrystalline elastic constants has been investigated in details. The computed B/G ratios show that all Sc₃AC compounds are brittle. We have estimated the sound velocities in the principal directions. Through the quasi-harmonic Debye model, in which the phononic effects are taken into account, the temperature and pressure effects on the lattice constant, bulk modulus, heat capacity and Debye temperature are performed.     

High-throughput first-principle calculations of the structural,mechanical, and electronic properties of cubic XTiO3 (X = Ca,Sr, Ba,Pb) ceramics under high pressure

High-throughput first-principle calculations are implemented to study the structural, mechanical, and electronic properties of cubic XTiO₃ (X = Ca, Sr, Ba, Pb) ceramics under high pressure. The effects of applied pressure on physical parameters, such as elastic constants, bulk modulus, Young's modulus, shear modulus, ductile-brittle transition, elastic anisotropy, Poisson's ratio, and band gap, are investigated. Results indicate that high pressure improves the resistance to bulk, elastic, and shear deformation for XTiO₃ ceramics. Pugh's ratios B/G reveal that CaTiO₃ and PbTiO₃ ceramics are ductile, but SrTiO₃ and BaTiO₃ ceramics are brittle under the ground state. The brittle-to-ductile transition pressures are 24.26 GPa for SrTiO₃ and 43.23 GPa for BaTiO₃. Under high pressure, the strong anisotropy promotes the cross-slip process of screw dislocations, and then enhances the plasticity of XTiO₃ ceramics. Meanwhile, XTiO₃ (X = Ca, Sr, Ba) is intrinsically an indirect-gap ceramic, but PbTiO₃ is a direct-gap ceramic. High pressure increases the band gap of XTiO₃ (X = Ca, Sr, Ba) ceramic, but decreases that of PbTiO₃ ceramic. This work is helpful for designing and applying XTiO₃ ceramics under high pressure.     

Low-compressibility and hard material carbon nitride imide C2N2(NH): First principles calculations

First principles calculations are performed to investigate the structural, mechanical, and electronic properties of C₂N₂(NH). Our calculated lattice parameters are in good agreement with the experimental data and previous theoretical values. Orthorhombic C₂N₂(NH) phase is found to be mechanically stable at an ambient pressure. Based on the calculated bulk modulus and shear modulus of polycrystalline aggregate, C₂N₂(NH) can be regarded as a potential candidate of ultra-incompressible and hard material. Furthermore, the elastic anisotropy and Debye temperatures are also discussed by investigating the elastic constants and moduli. Density of states and electronic localization function analysis show that the strong C-N covalent bond in CN₄ tetrahedron is the main driving force for the high bulk and shear moduli as well as small Poisson's ratio of C₂N₂(NH).     

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 studies of Al-Ni intermetallic compounds

The structural properties, heats of formation, elastic properties, and electronic structures of Al-Ni intermetallic compounds are analyzed here in detail by using density functional theory. Higher calculated absolute values of heats of formation indicate a very strong chemical interaction between Al and Ni for all Al-Ni intermetallic compounds. According to the computational single crystal elastic constants, all the Al-Ni intermetallic compounds considered here are mechanically stable. The polycrystalline elastic modulus and Poisson's ratio have been deduced by using Voigt, Reuss, and Hill (VRH) approximations, and the calculated ratio of shear modulus to bulk modulus indicated that AlNi, Al₃Ni, AlNi₃ and Al₃Ni₅ compounds are ductile materials, but Al₄Ni₃ and Al₃Ni₂ are brittle materials. With increasing Ni concentration, the bulk modulus of Al-Ni intermetallic compounds increases in a linear manner. The electronic energy band structures confirm that all Al-Ni intermetallic compounds are conductors.     

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.     

EuS高压相变发其弹性和热力学性质

采用平面波赝势密度泛函理论,利用第一性原理的方法研究了EuS的晶体结构、高压相变以及弹性性质．计算结果和实验值以及前人利用不同计算模型得到的理论值相吻合．研究了EuS的弹性常数、弹性模量和弹性的各向异性等力学性质随压力变化的趋势．同时研究了泊松比、德拜温度及纵波和横波的弹性波速随压力的变化趋势．基于德拜模型,进而研究了EuS在0-800K和0-60GPa下相变前后的热膨胀系数、热熔、Gruneisen参数等热力学性质．     

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.     

The mechanical properties of crystalline cyclopentyl polyhedral oligomeric silsesquioxane

The anisotropic elastic constants of crystalline octacyclopentyl polyhedral oligomeric silsesquioxane (CpPOSS) were determined using molecular dynamics. The force field used for these calculations was shown to model accurately the rhombohedral and triclinic crystal structures of octasilsesquioxane and CpPOSS, respectively, as well as the vibrational frequencies of octasilsesquioxane. The moduli for CpPOSS are anisotropic, with a Reuss-averaged bulk modulus of 7.5 GPa, an isotropic averaged Young's modulus of 11.78 GPa, and an isotropic averaged shear modulus of 4.75 GPa. These isotropic averages or, alternatively, the full anisotropic stiffness tensor of the crystal can be used with micromechanical composite models to calculate the effective elastic properties of polymer nanocomposites that contain crystalline aggregates of CpPOSS.