Structural,elastic, electronic,optical and thermoelectric properties of the Zintl-phase Ae3AlAs3 (Ae = Sr,Ba)

First-principles calculations were performed to investigate the structural, elastic, electronic, optical and thermoelectric properties of the Zintl-phase Ae₃AlAs₃ (Ae = Sr, Ba) using two complementary approaches based on density functional theory. The pseudopotential plane-wave method was used to explore the structural and elastic properties whereas the full-potential linearised augmented plane wave approach was used to study the structural, electronic, optical and thermoelectric properties. The calculated structural parameters are in good consistency with the corresponding measured ones. The single-crystal and polycrystalline elastic constants and related properties were examined in details. The electronic properties, including energy band dispersions, density of states and charge-carrier effective masses, were computed using Tran-Blaha modified Becke-Johnson functional for the exchange-correlation potential. It is found that both studied compounds are direct band gap semiconductors. Frequency-dependence of the linear optical functions were predicted for a wide photon energy range up to 15 eV. Charge carrier concentration and temperature dependences of the basic parameters of the thermoelectric properties were explored using the semi-classical Boltzmann transport model. Our calculations unveil that the studied compounds are characterised by a high thermopower for both carriers, especially the p-type conduction is more favourable.     

The under-pressure behaviour of mechanical,electronic and optical properties of calcium titanate and its ground state thermoelectric response

Abstract

In this study, the elastic, electronic, optical and thermoelectric properties of CaTiO₃ perovskite oxide have been investigated using first-principles calculations. The generalised gradient approximation (GGA) has been employed for evaluating structural and elastic properties, while the modified Becke Johnson functional is used for studying the optical response of this compound. In addition to ground state physical properties, we also investigate the effects of pressure (0, 30, 60, 90 and 120 GPa) on the electronic structure of CaTiO₃. The application of pressure from 0 to 90 GPa shows that the indirect band gap (Γ-M) of CaTiO₃ increases with increasing pressure and at 120 GPa it spontaneously decreases transforming cubic CaTiO₃ to a direct (Γ-Γ) band gap material. The complex dielectric function and some optical parameters are also investigated under the application of pressures. All the calculated optical properties have been found to exhibit a shift to the higher energies with the increase of applied pressure suggesting potential optoelectronic device applications of CaTiO₃. The thermoelectric properties of CaTiO₃ have been computed at 0 GPa in terms of electrical conductivity, thermal conductivity and Seebeck coefficient.     

Structural,elastic, thermodynamic and electronic properties of LuX (X = N,Bi and Sb) compounds: first principles calculations

ABSTRACT

The structural, electronic, elastic and thermodynamic properties of LuX (X = N, Bi and Sb) based on rare earth into phases, Rocksalt (B1) and CsCl (B2) have been investigated using full-potential linearized muffin-tin orbital method (FP-LMTO) within density functional theory. Local density approximation (LDA) for exchange-correlation potential and local spin density approximation (LSDA) are employed. The structural parameters as lattice parameters a₀, bulk modulus B, its pressure derivate B’ and cut-off energy (E_c) within LDA and LSDA are presented. The elastic constants were derived from the stress–strain relation at 0 K. The thermodynamic properties for LuX using the quasi-harmonic Debye model are studied. The temperature and pressure variation of volume, bulk modulus, thermal expansion coefficient, heat capacities, Debye temperature and Gibbs free energy at different pressures (0–50 GPa) and temperatures (0–1600 K) are predicted. The calculated results are in accordance with other data.     

First-principles study of structural,elastic, electronic and thermodynamic properties of topological insulator Bi2Se3 under pressure

The structural, elastic, electronic and thermodynamic properties of the rhombohedral topological insulator Bi₂Se₃ are investigated by the generalized gradient approximation (GGA) with the Wu–Cohen (WC) exchange-correlation functional. The calculated lattice constants agree well with the available experimental and other theoretical data. Our GGA calculations indicate that Bi₂Se₃ is a 3D topological insulator with a band gap of 0.287 eV, which are well consistent with the experimental value of 0.3 eV. The pressure dependence of the elastic constants C_ij, bulk modulus B, shear modulus G, Young’s modulus E, and Poisson’s ratio σ of Bi₂Se₃ are also obtained successfully. The bulk modulus obtained from elastic constants is 53.5 GPa, which agrees well with the experimental value of 53 GPa. We also investigate the shear sound velocity V_S, longitudinal sound velocity V_L, and Debye temperature Θ_E from our elastic constants, as well as the thermodynamic properties from quasi-harmonic Debye model. We obtain that the heat capacity C_v and the thermal expansion coefficient α at 0 GPa and 300 K are 120.78 J mol^?1 K^?1 and 4.70 × 10^?5 K^?1, respectively.     

Ab initio study of the structural,electronic, elastic and thermal conductivity properties of SrClF with pressure effects

Abstract

SrClF is an important optical crystal and can be used as pressure gauge in diamond anvil cell at high pressure. In this work, we performed a systematic study on the structural, electronic and elastic properties of SrClF under pressure, as well as its thermal conductivity, by first-principles calculation. Different exchange-correlation functionals were tested and PBESOL was finally chosen to study these properties of SrClF. Studies reveal that SrClF has a bulk modulus of about 56.2 GPa (by fitting equation of states) or 54.3 GPa (derived from elastic constants), which agree well with the experimental result. SrClF is mechanically and dynamically stable up to 50 GPa. Its elastic constants increase with the applied pressure, but its mechanical anisotropy deteriorates as the pressure increases. Investigation of its electronic properties reveals that SrClF is a direct band-gap insulator with a gap value of 5.73 eV at 0 GPa, which decreases with the increasing pressure and the reason is found by analysing the partial density of states. Based on the calculated phonon dispersion curves, thermal conductivity of SrClF is predicated. At ambient conditions, the predicted thermal conductivity is about 3.74 Wm^?1 K^?1, while that obtained using the simplified Slack model give a slightly larger value of 4.62 Wm^?1 K^?1.     

Elastic,mechanical, electronic properties and hardness of Nb2AsC from first principles

The study aims at the elastic, mechanical, electronic properties and hardness of Nb₂AsC using first principles based on the density functional theory method within the generalised gradient approximation. The calculated lattice parameters of Nb₂AsC are in good agreement with the experimental data. The five independent elastic constants are firstly calculated as a function of pressure, and our results indicate that it is mechanically stable in the applied pressure. The elastic anisotropy is examined through the computation of the direction dependence of Young's modulus. The pressure dependences of the bulk modulus, shear modulus, average velocity of acoustic waves and Debye temperature of Nb₂AsC are systematically investigated. The band structure and density of states are discussed, and the results show that the strong hybridisations C p–Nb d and As p–Nb d would be beneficial to the structure stability of Nb₂AsC. Based on the Mulliken population analysis, the hardness of Nb₂AsC is predicted.     

Structural,elastic, electronic,andoptical properties of layered TiNX (X = F,Cl, Br,I) compounds: a density functional theory study

ABSTRACT

Titanium nitride halides, TiNX (X = F, Cl, Br, I) in the α-phase (orthorhombic) are exciting quasi two-dimensional (2D) electronic systems exhibiting a fascinating series of electronic ground states. Pristine TiNX are semiconductors with varying energy gaps and possess attractive properties for potential applications in optoelectronics, photovoltaics, and thermoelectrics. Alkali metal intercalated TiNCl becomes superconducting at reasonably high temperature. We have revisited the electronic band structure of TiNX using density functional theory (DFT) based calculations. The atomic orbital resolved partial electronic energy densities of states are calculated together with the total density of states (TDOS). The structural and elastic properties have been investigated in details for the first time. The elastic anisotropy has been explored. The optical properties of TiNX are studied for the first time. The Debye temperatures have been calculated and the related thermal and phonon parameters are discussed. The calculated physical parameters are compared with existing theoretical and experimental results and showed fair agreement. TiNX are found to reflect electromagnetic radiation strongly in the mid ultraviolet region. The elastic properties show high degree of anisotropy. The effect of halogen atoms on various structural, elastic, electronic, and thermal properties in TiNX are also discussed in detail.     

Structural, electronic and elastic properties of Ti2TlC, Zr2TlC and Hf2TlC

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.      

Structural,electronic, optical and elastic properties of the complex K2PtCl6-structure hydrides ARuH6 (A = Mg,Ca, Sr and Ba): first-principles study

We report a systematic study of the structural, electronic, optical and elastic properties of the ternary ruthenium-based hydrides A₂RuH₆ (A = Mg, Ca, Sr and Ba) within two complementary first-principles approaches. We describe the properties of the A₂RuH₆ systems looking for trends on different properties as a function of the A sublattice. Our results are in agreement with experimental ones when the latter are available. In particular, our theoretical lattice parameters obtained using the GGA-PBEsol to include the exchange-correlation functional are in good agreement with experiment. Analysis of the calculated electronic band structure diagrams suggests that these hydrides are wide nearly direct band semiconductors, with a very slight deviation from the ideal direct-band gap behaviour and they are expected to have a poor hole-type electrical conductivity. The TB-mBJ potential has been used to correct the deficiency of the standard GGA for predicting the optoelectronic properties. The calculated TB-mBJ fundamental band gaps are about 3.53, 3.11, 2.99 and 2.68 eV for Mg₂RuH₆, Ca₂RuH₆, Sr₂RuH₆ and Ba₂RuH₆, respectively. Calculated density of states spectra demonstrates that the topmost valence bands consist of d orbitals of the Ru atoms, classifying these materials as d-type hydrides. Analysis of charge density maps tells that these systems can be classified as mixed ionic-covalent bonding materials. Optical spectra in a wide energy range from 0 to 30 eV have been provided and the origin of the observed peaks and structures has been assigned. Optical spectra in the visible range of solar spectrum suggest these hydrides for use as antireflection coatings. The single-crystal and polycrystalline elastic moduli and their related properties have been numerically estimated and analysed for the first time.     

Ab initio modelling of band states in doped diamond

Presented in this study is an analysis of the electronic properties of doped diamond calculated using the Vienna ab initio simulation package, employing density functional theory within the generalized-gradient approximation. The dopants studied here have been inserted substitutionally into a 64-atom diamond supercell and include the single-electron acceptors boron and aluminium, the single-electron donors nitrogen and phosphorus and the double-electron donors oxygen and sulphur. Co-doping of diamond with sulphur and boron has also been briefly examined. The doped supercells have been relaxed, followed by calculation of electronic properties from the electronic density of states such as the indirect bandgap E _g, the valence bandwidth and an examination of the acceptor and donor states in the bandgap. It is anticipated that this study will provide a useful comparison of the third- and fourth-row donors and acceptors in diamond.     

First-principles study of structural,mechanical, lattice dynamical and thermal properties of nodal-line semimetals ZrXY (X=Si,Ge; Y=S,Se)

Abstract

The nodal-line semimetals are new and very promising materials for technological applications. To understand their structural, mechanical, lattice dynamical and thermal properties in detail, we have investigated theoretical study of ZrXY (X = Si,Ge; Y = S,Se) using Density Functional Theory for the first time. Obtained lattice parameters are in excellent agreement with previous experimental data. These nodal-line semimetals obey the mechanical stability conditions for tetragonal structure. We obtain Bulk modulus, Shear modulus, Poisson’s ratio, Pugh ratio, sound velocities and thermal conductivity using elastic constant. All the materials behave in brittle manner. Poisson’s ratio data and Bader charge analysis results indicate that the ionic bonding characters are dominant. Next, the lattice dynamical properties are calculated. Phonon density of states shows that nodal-line semimetals ZrXY are also dynamically stable in the tetragonal structure. Raman and IR active phonon modes are determined. Highest optical mode at gamma point corresponds to A_2u (IR active) and E_g (Raman active) modes for ZrXSe and ZrXS, respectively. Based on phonon density of states, thermal properties such as Helmholtz free energy, entropy, heat capacity at constant volume and Debye temperature are also presented and discussed.     

钒基固溶体储氢材料弹性性质第一性原理研究

采用基于密度泛函理论的第一性原理赝势平面波方法,计算了（59Cr-41Ti）_100－xV_x（x=5,15,30,60,80,100）六种钒基储氢合金的晶格常数、弹性性质和电子态密度,计算结果与实验值符合较好.发现当x=60时的钒基合金具有较好弹性性质,杨氏模量为14930 GPa,切变模量为5442 GPa及体弹模量为19396 GPa.结合实验循环性能分析认为在吸放氢过程中合金已经发生塑性变形,弹性 关键词： 钒基固溶体 储氢合金材料 密度泛函理论 弹性性质     

Ab initio study of the linear and nonlinear optical responses in BiAlO3

The linear and non-linear optical properties of BiAlO₃ are studied by employing the density functional perturbation theory within the local density and generalized gradient approximations. The computations are based on the electronic structure obtained within density functional theory. The optical properties such as the dielectric function, refractive index, spectral reflectivity, absorption coefficient and electron energy-loss spectrum are obtained in the energy region of up to 30 eV. The calculated value of the birefringence for BiAlO₃ shows that it is a uniaxial negative crystal and has a large birefringence. We also report our studies on the second harmonic generation response coefficient over a large frequency range for BiAlO₃ crystal. The predicted second-order optical spectra indicate pronounced structures related to of 1ω and 2ω frequency resonances. Furthermore, the non-linear optic and linear electro-optic coefficients are computed by employing 2n + 1 theorem applied to an electric-field dependent energy functional. The results are compared with the available calculations.     

Structural,elastic, electronic and optical properties of platinum-based superconductor SrPt3P under pressure: a first-principles study

The structural, elastic, electronic and optical properties of the platinum-based superconductor SrPt₃P under pressure are investigated by the generalized gradient approximation with the Perdew–Burke–Ernzerhof exchange-correlation functional in the framework of density-functional theory. The calculated structural parameters (a, c) and the primitive cell volume V of SrPt₃P at the ground state are in good agreement with the available experimental data and seem to be better than other calculated results. The pressure dependences of the elastic constants \mathop C\nolimits_{ij}, bulk modulus B, shear modulus G, Young’s modulus E and Poisson’s ratio σ of SrPt₃P are also obtained successfully. The computed elastic constants indicate that SrPt₃P is mechanically stable up to 100 GPa. The obtained B/G is 2.56 at the ground state, indicating that SrPt₃P behaves in a ductile manner. The ratio B/G also increases with growing pressures, indicating that the structure becomes more and more ductile. Even though SrPt₃P is an ionic-covalent crystal, the obtained density of states shows that it has metallic characteristic. These conclusions can be further demonstrated by analysing the charge and Mulliken population. In addition, we have investigated the dielectric function and the loss function. It is found that the dielectric function in (E||x, E||y) is isotropic, whereas the directions (E||x, E||z) are anisotropic; the effect of pressure on the loss function of the deep ultraviolet region gradually increases as the pressure increases.     

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

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.     

An ab initio study of the structural,elastic, electronic and optical properties of the newly synthesized nitridoaluminate LiCaAlN2

The structural parameters, elastic constants, electronic structure and optical properties of the recently reported monoclinic quaternary nitridoaluminate LiCaAlN₂ are investigated in detail using the ab initio plane-wave pseudopotential method within the generalized gradient approximation. The calculated equilibrium structural parameters are in excellent agreement with the experimental data, which validate the reliability of the applied theoretical method. The chemical and structural stabilities of LiCaAlN₂ are confirmed by calculating the cohesion energy and enthalpy of formation. Chemical band stiffness is calculated to explain the pressure dependence of the lattice parameters. Through the band structure calculation, LiCaAlN₂ is predicted to be an indirect band gap of 2.725 eV. The charge-carrier effective masses are estimated from the band structure dispersions. The frequency-dependent dielectric function, absorption coefficient, refractive index, extinction coefficient, reflectivity coefficient and electron energy loss function spectra are calculated for polarized incident light in a wide energy range. Optical spectra exhibit a noticeable anisotropy. Single-crystal and polycrystalline elastic constants and related properties, including isotropic sound velocities and Debye temperatures, are numerically estimated. The calculated elastic constants and elastic compliances are used to analyse and visualize the elastic anisotropy of LiCaAlN₂. The calculated elastic constants demonstrate the mechanical stability and brittle behaviour of the considered material.     

缺陷黄铜矿结构Xga2S4 (X=Zn,Cd, Hg)晶体电子结构和光学性质的第一性原理研究

采用基于密度泛函理论(DFT)的第一性原理超软赝势方法对缺陷黄铜矿结构XGa₂S₄ (X=Zn, Cd, Hg)晶体的晶格结构、电学以及光学性质进行了对比研究. 分析比较了它们的晶格常数、键长、能带结构、态密度、介电函数、折射率和反射系数等性质, 并总结其变化趋势. 结果表明: 这三种材料的光学性质在中间能量区域(4 eV–10 eV)表现出较强的各向异性, 而在低能区域(<4 eV)和高能区域(>10 eV)各向异性较弱. ZnGa₂S₄和HgGa₂S₄两种材料的折射率曲线在等离子体频率ω_p处有一明显的拐点, 反射系数在ω_p处达到最大值后急剧下降. 三种晶体的强反射峰均处于紫外区域, 因此可以用作紫外光屏蔽或紫外探测材料. 关键词： 缺陷黄铜矿结构 电子结构 光学性质 第一性原理计算     

Structural and electronic properties of InNxP1-x alloy in full range (0 ≤ x ≤1)

We have performed first-principles method to investigate structural and electronic properties of InN_xP_1?x ternary semiconductor alloy in full range (0 ≤ x ≤ 1) using density functional theory. We have used modified Becke–Johnson potential to obtain accurate band gap results. From the electronic band structure calculation we have found that InN_xP_1?x become metal between 47 and 80% of nitrogen concentration. Additional to our band gap calculations, we have also used the band anticrossing model. The band anticrossing model supplies a simple, analytical expression to calculate the physical properties, such as the electronic and optical properties, of III-N_xV_1?x alloys. The knowledge of the electron density of states is required to understand and clarify some properties of materials such as the band structures, bonding character and dielectric function. In order to have a deeper understanding of these properties of the studied materials, the total and partial density of states has been calculated. Finally, we have calculated the total bowing parameter b of studied alloys, together with three contributions b_VD, b_CE, and b_SR due to volume deformation, different atomic electron negativities and structural relaxation, respectively.     

The mechanical,thermodynamic and electronic properties of Al3Nb with DO22 structure: A first-principles study

The lattice constants, elastic properties, electronic structure and thermodynamic properties of Al₃Nb with DO₂₂ structure have been investigated by the first-principles calculation. The calculated lattice constants were consistent with the experimental values, and the structural stability was also studied from the energetic point of view. The single-crystal elastic constants (C_ij) as well as polycrystalline elastic parameters (bulk modulus B, shear modulus G, Young's modulus E, Poisson's ratio υ and anisotropy value A) were calculated, and brittleness of Al₃Nb was discussed in detail. Besides, the electronic structure of tetragonal Al₃Nb was studied, which indicates a mixture of metallic bond and covalent bond in Al₃Nb and reveals the underlying mechanism of the stability and elastic properties of Al₃Nb. Finally, the thermodynamic properties of Al₃Nb were calculated and the physical properties such as heat capacity and Debye temperature were predicted within the quasi-harmonic approximation.