First-principles study of structural,elastic, electronic and optical properties of RDX under pressure

ABSTRACT

The influences of pressure on structural, elastic, electronic and optical properties of α-RDX under pressure from 0 to 40?GPa have been investigated by performing first-principles calculations. The obtained structural parameters based on the GGA-PBE+G calculations are consistent with previous experimental values. The results of B/G, C₁₂-C₄₄ and Poisson's ratio show that α-RDX has changed to ductility under pressure between 0 and 5?GPa. The obvious rotation of NO₂ group in the equatorial position appears, especially in the range of pressure from 10 to 15?GPa, which influences the elastic and mechanical properties of α-RDX. Moreover, we find that the electrons of α-RDX become more active under higher pressure by comparing the curves of DOS under different pressure. Furthermore, the anisotropy of optical properties under different pressures has been shown.     

First-principles analysis of the structural,electronic, and elastic properties of cubic organic-inorganic perovskite HC(NH_2)_2PbI_3

The structural, electronic, and elastic properties of cubic HC(NH_2)_2PbI_3 perovskite are investigated by density functional theory using the Tkatchenko–Scheffler pairwise dispersion scheme. Our relaxed lattice parameters are in agreement with experimental data. The hydrogen bonding between NH_2 and I ions is found to have a crucial role in FAPbI_3 stability. The first calculated band structure shows that HC(NH_2)_2PbI_3 has a direct bandgap(1.02 eV) at R-point, lower than the bandgap(1.53 eV) of CH_3NH_3PbI_3. The calculated density of states reveals that the strong hybridization of s(Pb)–p(I) orbital in valence band maximum plays an important role in the structural stability. The photo-generated effective electron mass and hole mass at R-point along the R–Γ and R–M directions are estimated to be smaller: m_e~*= 0.06 m0 and m_h~*= 0.08 m0 respectively, which are consistent with the values experimentally observed from long range photocarrier transport. The elastic properties are also investigated for the first time, which shows that HC(NH_2)_2PbI_3 is mechanically stable and ductile and has weaker strength of the average chemical bond. This work sheds light on the understanding of applications of HC(NH_2)_2PbI_3 as the perovskite in a planar-heterojunction solar cell light absorber fabricated on flexible polymer substrates.     

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.     

AsI_3电子结构与弹性性质的第一性原理研究

采用基于密度泛函理论的第一性原理赝势方法,对AsI3的平衡态晶格常数、弹性常数和电子结构进行了研究.研究结果表明,R-3结构的AsI3在零压下是稳定的,优化得到的平衡结构参数与实验值符合的很好.AsI3是脆性材料,具有大的弹性各向异性特征.R-3相AsI3的块体模量、剪切模量和杨氏模量分别为14.2GPa,9.8GPa和23.9GPa,泊松比为0.22,德拜温度是163K.能带结构计算表明,AsI3是带隙为2.34eV的间接带隙半导体.AsI3的化学键是弱共价键和离子键的混合.     

AsI3电子结构与弹性性质的第一性原理研究

采用基于密度泛函理论的第一性原理赝势方法,对AsI3的平衡态晶格常数、弹性常数和电子结构进行了研究。研究结果表明,R-3结构的AsI3在零压下是稳定的,优化得到的平衡结构参数与实验值符合的很好。AsI3是脆性材料,具有大的弹性各向异性特征。R-3相AsI3的块体模量、剪切模量和杨氏模量分别为14.2 GPa, 9.8 GPa和23.9 GPa,泊松比为0.22,德拜温度是163 K。能带结构计算表明,AsI3是带隙为2.34 eV的间接带隙半导体。AsI3的化学键是弱共价键和离子键的混合。     

Stability,elastic anisotropy,and electronic properties of Ca_2C_3

The systematic investigations of the mechanical, elastic, and electronic properties, and stability of the newly synthesized monoclinic C2/m-Ca_2C_3 are performed, based on the first-principles calculations. Ca_2C_3 is found to be mechanically and dynamically stable only from 0 GPa to 24 GPa. The elastic anisotropy studies show that Ca_2C_3 exhibits the elastic anisotropy increasing with the augment of pressure. Furthermore, using the HSE06 hybrid functional, the electronic properties of Ca_2C_3 under pressure are calculated. The structure can be regarded as a quasi-direct band gap semiconductor, and the pressure-induced direct-indirect band gap transition is studied in detail.     

First-principles investigation of structural,mechanical, electronic,and bonding properties of NaZnSb

The structural, mechanical, electronic, and bonding properties and phase transition of NaZnSb are explored using the generalized gradient approximation based on ab initio plane-wave pseudopotential density functional theory. With the help of the quasi-harmonic Debye model, we probe the Grüneisen parameter, thermal expansivity, heat capacity, Debye temperature, and entropy of NaZnSb in the tetragonal phase. The results indicate that the lattice constants and the bulk modulus and its first pressure derivative agree well with the available theoretical and experimental data. NaZnSb in its ground state structure exhibits a distinct energy gap of about 0.41 eV, which increases with increasing pressure. Our conclusions are consistent with the theoretical predictions obtained by the ABINIT package, but are different from those obtained through the tight-binding linear muffin-tin orbital method. As a result, further experimental and theoretical researches need to be carried out. For the purpose of providing a comparative and complementary study for future research, we first investigate the thermodynamic properties of NaZnSb.     

First-principles study of the structural,elastic, and optical properties for Sr0.5Ca0.5TiO3

A detailed theoretical study of the structural, elastic, and optical properties for Sr0.5Ca0.5TiO3 is carried out by first- principles calculations. The band structure exhibits a direct bandgap of 2.08 eV at the F point in the Brillouin zone. The bulk modulus, shear modulus, Young＇s modulus, and Poisson＇s ratio are derived based on the calculated elastic constants. The bulk modulus B = 153 GPa and shear modulus G = 81GPa are in good agreement with available experimental data. Poisson＇s ratio v = 0.275 suggests that Sr0.sCa0.sTiO3 should be classified as being a ductile material. Using the electronic band structure and density of states, we analyze the interband contribution to the optical properties. The real and imaginary parts of the dielectric function, as well as the optical properties such as the optical absorption coefficient, refractive index, extinction coefficient, and energy-loss spectrum are calculated. The static dielectric constant ε1 （0） and the refractive index n（0） are also investigated.     

Cr2MC(M=Al, Ga)的电子结构、弹性和热力学性质的第一性原理研究

本文使用第一性原理的GGA/RPBE方法研究了Cr₂MC(M=Al, Ga)的电子结构、弹性和热力学性质. 研究发现两个化合物的体积压缩性几乎相同, 并且证实了在0—50 GPa范围内c轴始终较a轴更难以压缩并且结构始终是稳定的. 通过对内坐标的研究发现了Cr₂AlC中Cr离子的内坐标始终大于Cr₂GaC中Cr离子的内坐标. 使用准谐德拜模型得到的体弹模量在0 GPa下随着温度的升高而减小, 而在300 GPa下则随着温度的升高而增大. 对德拜温度的研究发现Cr₂GaC的值小于Cr₂AlC的值, 而对热膨胀系数、Grüneisen参数、熵和热容的计算发现Cr₂GaC的值大于Cr₂AlC的值. 对电子结构的分析发现Cr₂GaC的s和p电子在费米能级处的值大于Cr₂AlC的s和p电子的值, 而其他离子的电子分布几乎一致.     

几种三元过渡金属碳化物弹性及电子结构的第一性原理研究

基于密度泛函理论平面波方法研究了六方WC型Re_xW_1－xC(x=1, 0.25, 0.75, 0),Re_0.5Os_0.5C和Os_0.5W_0.5C的晶体结构、弹性和电子结构性质.研究发现Re_0.25W_0.75C晶体具有优异的弹性性能及稳定性,其剪切模量(312 GPa)超过了所有其他实验合成和     

高压下RhB的相变、弹性性质、电子结构及硬度的第一性原理计算

采用密度泛函理论中的赝势平面波方法系统地研究了高压下RhB的结构相变、弹性性质、电子结构和硬度.分析表明,RhB在25.3 GPa时从anti-NiAs结构相变到FeB结构,这两种结构的弹性常数、体弹模量、剪切模量、杨氏模量和弹性各向异性因子的外压力效应明显.电子态密度的计算结果显示,这两种结构是金属性的,且费米能级附近的峰随着压强的增大向两侧移动,赝能隙变宽,轨道杂化增强,共价性增强,非局域化更加明显.此外,硬度计算结果显示,anti-NiAs-RhB的金属性比较弱,有着较高的硬度,属于硬质材料.     

闪锌矿GaN弹性性质、电子结构和光学性质外压力效应的理论研究

采用基于密度泛函理论(DFT)的第一性原理平面波赝势方法,结合广义梯度近似(GGA)下的RPBE和局域密度近似(LDA)的CA-PZ交换-关联泛函对闪锌矿结构的GaN在高压的性质进行了系统研究. 计算结果表明:弹性常数、体模量、杨氏模量和能隙都具有明显的外压力效应,计算结果与实验值和理论值很好的符合. 同时利用计算的能带结构和态密度系统分析了GaN的介电函数、折射率、反射率、吸收系数和能量损失函数等光学性质及其外压力效应. 分析结果为GaN的设计与应用提供了理论依据. 关键词： 第一性原理计算 电子结构 光学性质 闪锌矿GaN     

黑索金电子结构和光学性质的第一性原理研究

利用基于密度泛函理论的第一性原理方法对黑索金晶体的电子结构和光学性质进行了计算. 结果表明: 黑索金是能隙值为3.43 eV的绝缘体, 价带主要由C, N和O的2s与2p态构成, 而导带主要由N-2p和O-2p态构成; 静态介电函数ε₁(0)=1.38, 介电常数的虚部有5个峰值, 其中最大峰值在光子能量4.59 eV处, 并对造成这些峰值的可能的电子跃迁做了详细分析. 利用能带结构和态密度分析了黑索金的光反射系数、吸收系数及能量损失函数等光学性质, 发现黑索金是对光吸收、反射及能量损失不敏感的材料. 关键词： 黑索金 第一性原理 电子结构 光学性质     

CaB6电子结构及光学性质的第一性原理计算

采用基于密度泛函理论的第一性原理的分子动力学方法系统地计算了温度为300K时CaB6基态的电子结构、态密度和光学性质.能带结构分析表明CaB6属于一种直接带隙半导体;其导带主要由Ca的3d态电子构成,价带主要由B的2p态电子构成,静态介电常数ε1(0)=7.8,折射率n(0)=2.8,吸收系数最大峰值为4.37×105...     

Nb掺杂对Mo2FeB2弹性、硬度和电子结构影响的第一性原理计算

Mo₂FeB₂具有耐高温、耐磨、高强度,是一种良好的硼基金属陶瓷材料,在模具领域有很广阔的应用前景.本文采用第一性原理计算的方法,研究了Nb元素掺杂Mo₂FeB₂合金的结构稳定性、弹性、硬度和电子结构.结合能和生成焓的计算结果表明,Nb在Mo₂FeB₂中更容易占据Fe位置,并且在Fe位掺Nb的Mo₂FeB₂比在Mo位处掺Nb具有更好的力学性能.此外,计算结果还表明,Nb掺杂可以提高Mo₂FeB₂的剪切模量、杨氏模量、体积模量和硬度,但塑性略有下降,合适的掺杂浓度应为2.5 at.%.电子结构计算结果表明,Nb掺杂Mo₂FeB₂力学性能的提高可归因于Nb-B共价键的形成.     

BaHfO3纳米薄膜电子结构、光学和弹性性质的第一性原理研究

采用基于密度泛函理论的第一性原理方法,在局域密度近似（LDA）下研究了厚度为0.626～2.711nm (100)面BaHfO3薄膜的电子结构、光学和弹性性质．电子结构和光学性质计算结果表明：以BaO为表面层原子的BaHfO3纳米薄膜均为直接带隙半导体材料,带隙随薄膜厚度减小而逐渐减小,表现出明显的量子尺寸效应,此时薄膜的光学吸收边发生红移,吸收带出现窄化现象．以HfO2作为表面层原子的BaHfO3薄膜则属于间接带隙半导体材料,且带隙随薄膜厚度减小而微弱增加．弹性性质计算结果表明：体弹模量、剪切模量和杨氏模量等表征材料硬度的力学参数均随BaHfO3纳米薄膜厚度减小而显著减小,呈现尺寸效应．电荷密度分布分析揭示了薄膜厚度改变了BaHfO3纳米薄膜的价健特性,这是材料硬度改变的内在原因．该研究结果为BaHfO3纳米薄膜材料的设计与应用提供了理论依据．     

Theoretical investigation of the elastic,electronic, thermodynamic and optical properties of the zinc-blende structure AlN under high pressure

The elastic, electronic, thermodynamic and optical properties of the zinc-blende structure aluminum nitride (AlN) under high pressure have been investigated using first-principles calculations. The dependencies of the elastic constants, the bulk modulus, the shear modulus and energy gaps on the applied pressure are presented, and the results are in good agreement with comparable experimental and theoretical values. Also, the energy band structure and density of states under high pressure have been analysed. Furthermore, the optical constants, including the dielectric function, optical reflectivity, refractive index and electron energy loss, are discussed for radiation up to 50 eV.     

First-principles investigation of N-Ag co-doping effect on electronic properties in p-type ZnO

The geometric structure, band structure and density of states of pure, Ag-doped, N-doped, and N--Ag codoped wurtzite ZnO have been investigated by the first-principles ultra-soft pseudopotential method based on the density functional theory. The calculated results show that the carrier concentration is increased in the ZnO crystal codoped by N and Ag, and the codoped structure is stable and is more in favour of the formation of p-type ZnO.     

TiO$lt;sub$gt;2$lt;/sub$gt;纳米管电子结构和光学性质的第一性原理研究

运用基于密度泛函理论的第一性原理方法, 系统研究了小尺寸锐钛矿相(n,0)型TiO₂纳米管(D<16 Å)的几何构型、电子结构和光学性质. 结果表明: 随着管径增大, 体系单位TiO₂分子的形成能降低, 体系趋于稳定; 在管径14 Å左右, (n,0)型TiO₂纳米管会发生一次构型的转变. 能带分析显示, TiO₂纳米管的电子态比较局域化, 小管径下(D<14 Å)其导电性更好; 随着构型的转变, TiO₂纳米管由直接带隙转变为间接带隙, 并且带隙值随着管径的增大而增大, 这是由于π轨道重叠效应的影响大于量子限域效应所导致的结果. 两种效应的竞争, 使得TiO₂纳米管的介电函数虚部ε₂ (ω)谱的峰值位置随管径增大既可能红移也可能蓝移, 管径大于9 Å (即(8, 0)管)之后, TiO₂纳米管的光吸收会出现明显的增强. 关键词： 2纳米管')" href="#">TiO₂纳米管 第一性原理 电子结构 光学性质