Ab initio calculations of structural,elastic and electronic properties of Li2O2

The equilibrium structure of the compound Li₂O₂ has been obtained via minimization of the total energy within the local density approximation (LDA) based on density functional theory (DFT). The calculated lattice parameters are in excellent agreement with available values. The elastic properties of Li₂O₂ are investigated. Values of all independent elastic constants (C ₁₁, C ₁₂, C ₁₃, C ₃₃ and C ₄₄) as well as bulk moduli in the a and c directions are predicted. Our calculated elastic properties suggest that the compound Li₂O₂ is slightly anisotropic but can be considered as an isotropic material compared with other highly anisotropic materials. The electronic properties, including the density of states and energy band structure, are obtained and we find that this compound behaves as a semiconductor.     

Ab initio studies of the structural,elastic, electronic and thermal properties of NiTi2 intermetallic

First principles calculations were performed in the framework of the density functional theory (DFT) using the Full Potential–Linear Augment Plane Wave method (FP–LAPW) within the generalized gradient approximation (GGA) to predict the structural, electronic, elastic and thermal properties of NiTi₂ intermetallic compound. By using the Wien2k all-electron code, calculations of the ground state and electronic properties such as lattice constants, bulk modulus, presure derivative of bulk modulus, total energies and density of states were also included. The elastic constants and mechanical properties such as Poisson’s ratio, Young’s modulus and shear modulus are estimated from the calculated elastic constants of the single crystal. Through the quasi-harmonic Debye model, the preasure and temperature dependences of the linear expansion coefficient, bulk modulus and heat capacity have been investigated. Finally, the Debye temperature has been estimated from the average sound velocity according to the predicted polycrystal bulk properties and from the single crystal elastic constants.     

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.     

Ab initio study of structural,electronic and dynamical properties of MgAuSn

The structural and electronic properties of MgAuSn in the cubic AlLiSi structure have been studied, using density functional theory within the local density approximation. The calculated lattice constant for MgAuSn is found to be in good agreement with its experimental value. Our calculated electronic structure is also compared in detail with a recent tight-binding. A linear-response approach to density-functional theory is used to calculate the phonon spectrum and density of states for MgAuSn.     

Ab initio calculations of yttrium nitride: structural and electronic properties

Using first principles total energy calculations within the full-potential linearized augmented plane wave method, we have studied the structural and electronic properties of yttrium nitride (YN) in the three phases, namely wurtzite, caesium chloride and rocksalt structures. The calculations are performed at zero and under hydrostatic pressure. In agreement with previous findings, it is found that the favored phase for YN is the rocksalt-like structure. We predict that at zero pressure YN in the rocksalt structure is a semiconductor with an indirect bandgap of 0.8 eV. A phase transition from a rocksalt to a caesium chloride structure is found to occur at ∼134 GPa. Besides, a transition from an indirect (Γ−X) bandgap semiconductor to a direct (X−X) one is predicted at pressure of ∼84 GPa. For the electron effective mass of rocksalt YN, these are the first results, to our knowledge. The information derived from the present study may be useful for the use of YN as an active layer in electronic devices such as diodes and transistors.     

Ab initio study of structural,electronic,thermo-elastic and optical properties of Pt_3Zr intermetallic compound

Structural,elastic,electronic and optical properties of the Pt3Zr intermetallic compound are investigated using first principles calculations based on the density functional theory(DFT)within the generalized gradient approximation(GGA)and the local density approximation(LDA).The Pt3Zr compound is predicted to be of cubic L12 and hexagonal D024 structures.The calculated equilibrium ground-state properties(lattice parameters a and c,bulk modulus B and its pressure derivative B',formation enthalpy ΔH)of the Pt3Zr compound,for both cubic and hexagonal phases,show good agreement with the experimental results and other theoretical data.Elastic constants(C11,C12,C13,C33,C44,and C55)are calculated.The predicted elastic properties such as Young's modulus E and shear modulus GH,Poisson ratioν,anisotropic ratio A,Kleinman parameter ξ,Cauchy pressure(C12-C44),ratios B/C44 and B/G,and Vickers hardness Hv indicate the stiffness,hardness and ductility of the compound.Thermal characteristic parameters such as Debye temperature θD and melting temperature Tm are computed.Electronic properties such as density of states(DOS)and electronic specific heat γ are also reported.The calculated results reveal that the Fermi level is on the psedogap for the D024 structure and on the antibonding side for the L12 structure.The optical property functions(real partε1(ω)and imaginary part ε2(ω)of dielectric function),optical conductivity σ(ω),refraction index n(ω),reflectivity R(ω),absorption α(ω)and extinction coefficients k(ω)and loss function L(ω)are also investigated for the first time for Pt3Zr in a large gamme of energy from 0 to 70 eV.     

Ab initio investigation of the electronic structure of AgCl

The structural and electronic behavior of a prototype silver halide, namely AgCl, has been investigated by means of the full-potential linearized augmented plane wave method with the local density approximation. The aim of our study is to focus on the influence of the d metal orbitals through a detailed analysis of the electronic energies. The presence the d Ag orbitals leads to a strong hybridization between them and the p halogen ones, giving rise to specific electronic states organization and charge distribution. As expected from its rock-salt structure, AgCl is as an ionic compound characterized by a mixed p–d top valence band.     

Ab initio investigation into the structural, electronic and elastic properties of AlCu2TM (TM = Ti, Zr and Hf) ternary compounds

The Al-Cu-TM (TM = transition metal) alloy system has attracted great attention for both excellent glass-forming ability and its interesting physical properties. In this work, an investigation into the crystal, electrical and elastic properties of the AlCu₂TM (TM = Ti, Zr, and Hf) compounds has been conducted by first-principles calculations based on density-functional theory. The fully relaxed structure parameters of the AlCu₂TM compounds are in good agreement with previous experimental and other theoretical results. Besides, the cohesive energies of all the AlCu₂TM compounds have been evaluated. The energy band and densities of state of these compounds are also obtained. According to the calculated single crystal elastic constants, all the compounds are mechanically stable. The polycrystalline bulk moduli, shear moduli, Young’s moduli and Poisson’s ratio have been deduced by using Voigt-Reuss-Hill (VRH) approximations. The calculated negative Cauchy pressure and ratio of bulk modulus to shear modulus indicated that the AlCu₂TM compounds are ductile materials. The Debye temperatures of the AlCu₂TM compounds decrease with increasing the TM (Ti, Zr, and Hf) atomic number.     

非晶碳结构建模和电子结构的第一性原理研究

基于密度泛函理论，采用了一种更为精确的交换相关泛函OLYP(OPTX+LYP)，对密度范围从2.0到3.2 g/cm³的非晶碳进行结构建模. 模拟得到的5个碳网络结构无论从径向分布函数还是sp³含量都与实验符合得很好. 对非晶碳电子结构的研究表明费米能级附近的电子态密度主要是sp²碳原子的贡献. 随着密度的增加，sp³碳原子增加，费米能级附近的态密度越来越小. 小环结构增加了费米能级附近的电子态密度，缺陷态在费米能级形     

Ab initio investigation of the pressure influence on elastic properties of the GaS layered compound

From first principles, in the pressure range of 0–20 GPa, taking into account the structural phase transition at 3 GPa, all independent elastic constants of GaS compound have been calculated. From obtained data, the pressure dependences of the velocities of propagation of elastic waves in different symmetry directions have been determined. The values of averaged elastic moduli, Young’s modulus and Poisson’s ratio and their pressure dependence have also been calculated..     

Li_2NH晶体结构建模和电子结构的第一性原理研究

基于密度泛函理论的赝势-平面波方法,采用三种模型分别研究Li,N原子对N—H键方位的影响以及N—H键间的相互影响,得到了Li2NH的晶体结构和H原子的占位位置.计算结果表明:Li2NH晶体为层状结构,空间群为P42,晶胞中4个N—H键分为两层,层内N—H键为反平行排列,层间N—H键为垂直排列.态密度和电子局域函数(ELF)分析表明,N—H键呈明显的共价键特性,Li和N—H键呈明显的离子键相互作用.可逆储氢反应Li2NH+H2/LiNH2+LiH在温度0K时的反应焓为69.6kJ/molH2,与实验结果66kJ/molH2符合得较好.     

Ab initio investigation of the electronic and vibrational properties for the (CaLi)+ ionic molecule

A wide adiabatic study has been performed for numerous electronic states of CaLi⁺ molecular ion. The adiabatic potential energy curves and their spectroscopic constants (R_e, D_e, ω_e and T_e) have been calculated using an ab initio approach including a nonempirical pseudo-potential for the Ca and Li cores with the core polarisation potentials operator through full configuration interaction (FCI). Thereafter, the energies of vibrational levels and their spacing for all these states have been reported. In addition, the electric dipole moment curves have been investigated for the (1-19) Σ, (1-12) Π and (1-8) Δ electric states. Moreover it lets us check the extreme transition dipole moments (TDM). These behaviours of TDM are more accustomed to estimate the radiative lifetimes for all vibrational levels in 2¹Σ⁺ and 3¹Σ⁺ states. Also, the bound-bound and the bound-free contribution have been calculated precisely and by employing a Franck–Condon (FC) approximation.     

Ab initio study of structural and electronic properties of BiAlO3 and BiGaO3

The first principles within the full potential linearized augmented plane wave (FP-LAPW) method was applied to study the structural and electronic properties of cubic perovskite-type compounds BiAlO₃ and BiGaO₃. The lattice constant, bulk modulus, its pressure derivative, band structure and density of states were obtained. The results show that BiGaO₃ should exhibit higher hardness and stiffness than BiAlO₃. The Al–O or Ga–O bonds are typically covalent with a strong hybridizations as well as Bi–O ones that have a significant ionic character. Both materials are weakly ionic and exhibit wide and indirect band gaps, which are typical of insulators.     

非晶碳结构建模和电子结构的第一性原理研究

基于密度泛函理论,采用了一种更为精确的交换相关泛函OLYP(OPTX+LYP),对密度范围从2.0到3.2 g/cm³的非晶碳进行结构建模. 模拟得到的5个碳网络结构无论从径向分布函数还是sp³含量都与实验符合得很好. 对非晶碳电子结构的研究表明费米能级附近的电子态密度主要是sp²碳原子的贡献. 随着密度的增加,sp³碳原子增加,费米能级附近的态密度越来越小. 小环结构增加了费米能级附近的电子态密度,缺陷态在费米能级形 关键词： 非晶碳 密度泛函理论 电子结构