First principles calculation on ternary stannide phase narrow band gap semiconductor Na2MgSn

The electronic structures, chemical bonding, elastic and optical properties of the ternary stannide phase Na₂MgSn were investigated by using density-functional theory (DFT) within generalized gradient approximation (GGA). The calculated energy band structures show that Na₂MgSn is an indirect semiconductor material with a narrow band gap 0.126 eV. The density of state (DOS) and the partial density of state (PDOS) calculations show that the DOS near the Fermi level is mainly from the Na 2p, Mg 3p and Sn 5p states. Population analysis suggests that there are strongly bonded Mg-Sn honeycomb layers in Na₂MgSn. Basic physical properties, such as lattice constant, bulk modulus, shear modulus, elastic constants c_ij were calculated. The elastic modulus E and Poisson ratio v were also predicted. The results show that Na₂MgSn is mechanically stable soft material and behaves in a brittle manner. Detailed analysis of all optical functions reveals that Na₂MgSn is a better dielectric material, and reflectivity spectra show that Na₂MgSn promise as good coating materials in the energy regions 6.24–10.49 eV.     

极端不可压缩Re2P的电子结构、化学键及弹性性质的第一性原理研究

利用基于密度泛函理论（DFT）的广义梯度近似（GGA）,研究Co2P类型结构的极端不可压缩Re2P的电子结构、化学键和弹性性质。能带结构显示Re2P为金属性材料;态密度和分态密度的计算结果表明,费米能级附近的态密度主要来自Re-5d态;布居分析表明Re2P中的化学键具有以共价性为主的混合离子一共价特征。计算得到Re2P的晶格参数、体模量、剪切模量和单晶的弹性常数,由此导出弹性模量和泊松比。结果表明,Re2P是力学稳定的,且具有一定的脆性。     

BiOCuS电子结构、化学键和弹性性质的第一性原理研究(英文)

利用基于密度泛函理论(DFT)的广义梯度近似(GGA)研究四方相BiOCuS的电子结构、化学键和弹性性质。能带结构显示,BiOCuS为间接带隙半导体,带隙宽为0.503eV;态密度和分态密度的结果表明,费米能级附近的态密度主要来自Cu-3d态。布居分析表明,BiOCuS中的化学键具有以离子性为主的混合离子?共价特征。计算得到四方相BiOCuS的晶格参数、体模量、剪切模量和单晶的弹性常数,由此导出弹性模量和泊松比。结果表明,BiOCuS是力学稳定的,且具有一定的延展性。     

n型掺杂BaSnO3的电子结构和光学性能的第一性原理研究

基于密度泛函理论,从头计算了La以及Nb掺杂BaSnO3的稳定性、电子结构和光学性质。结果表明La以及Nb掺杂BaSnO3体系结构稳定,均为n型导电材料,在可见光区透过率大于80%,且La以及Nb掺杂BaSnO3明显改善了体系的导电性。计算结果为实验制备n型BaSnO3基透明导电材料提供了理论指导。     

过渡金属氢化物TMH（TM=Mo、TC、RU）的显微组织、电子特性和力学性能的第一性原理研究

通过基于广义梯度近似密度泛函理论的第一性原理研究过渡金属氢化物 TMH(TM =Mo、TC、RU)的显微组织、电子特性和力学性能。在被研究的5个晶体结构中,立方结构比六方晶结构更稳定。预测了不同过渡金属氢化物在高压下的相结构转变,如：MoH中从ZB结构到WC结构的转变、在TcH中从NaCl结构到NiAs结构的转变以及在RuH中从NaCl结构到ZB结构再到NiAs结构的转变。弹性常数的计算表明：三种氢化物的力学性能在环境压力下是稳定的。     

RhZr相结构稳定性和电子结构性质的第一性原理研究

用第一性原理计算研究RhZr两种晶体结构的结构稳定性和电子结构性质。采用基于第一性原理的平面波赝势法,分别用局域密度近似和广义梯度近似法,对晶体原子的结构进行优化,并分别对正交晶系RhZr和立方晶系RhZr的基态性质,如晶格参数、能态密度、形成能以及形成焓等进行计算。计算结果表明：正交晶系RhZr比立方晶系RhZr更容易生成,而且生成的正交晶系RhZr比立方晶系RhZr更稳定。能态密度计算结果表明：立方晶系RhZr比正交晶系RhZr稳定,是因为在立方晶系RhZr中不仅存在Rh？Zr还存在Rh？Rh或者Zr？Zr之间的相互作用键。由态密度分析还可看出,在费米面附近Rh的4d轨道与Zr的4d轨道存在较强的轨道杂化。     

First principles calculations on elasticity, electronic structure and bonding properties of antiperovskites ANTi3 (A = Al, In and Tl)

We use an ab initio pseudopotential plane wave (PP-PW) method within the generalized gradient approximation (GGA) and the local density approximation (LDA) to study the structural, elastic and electronic properties of the unexplored antiperovskite ANTi₃ compounds. The elastic constants C₁₁, C₁₂, C₄₄ and their pressure dependence are calculated. We derived the bulk, shear and Young's moduli for ideal monocrystalline and for polycrystalline ANTi₃ aggregates which we have classified as ductile in nature. Band structures reveal that these compounds are conductors. The covalent ionic bands nature is due to the strong hybridization between Ti 3d and N 2p states. The Ti 3d states play dominant roles near the Fermi levels for all these compounds. The energy difference between spin polarized calculations and the nonspin polarized calculations indicate that ANTi₃ compounds exhibit magnetism at their equilibrium lattice constants.     

Mg17Al12、Al2Y及Al2Ca相稳定性与弹性性能第一原理研究

采用基于密度泛函理论的Castep和Dmol程序软件包,计算了Mg17Al12、Al2Y及Al2Ca相的结构稳定性、弹性性能与电子结构。形成热和结合能计算结果表明:Al2Y具有最强的合金化形成能力和结构稳定性;热力学性质计算结果表明:在298~573 K温度范围内,Al2Y的Gibbs自由能始终最小,其结构热稳定性最好,Al2Ca次之,Mg17Al12最差,Y和Ca合金化Mg-Al系合金形成Al2Y及Al2Ca利于提高镁合金的高温抗蠕变性能;弹性常数的计算结果表明:3种金属间化合物均为脆性相,Mg17Al12的塑性最好;采用弹性常数计算结果预测的Al2Y熔点最高,其结构热稳定性最好。态密度和Mulliken电子占据数的计算结果表明:Al2Y结构最稳定的原因,主要源于体系在Fermi能级以下区域成键电子存在强烈的共价键作用。     

The first-principles calculations for the elastic properties of Zr2Al under compression

The first-principles calculations were applied to investigate the structural, elastic constants of Zr₂Al alloy with increasing pressure. These properties are based on the plane wave pseudopotential density functional theory (DFT) method within the generalized gradient approximation (GGA) for exchange and correlation. The result of the heat of formation of Zr₂Al crystal investigated is in excellent consistent with results from other study. The anisotropy, the shear modulus, and Young's modulus for the ideal polycrystalline Zr₂Al are also studied. It is found that (higher) pressure can significantly improve the ductility of Zr₂Al. Moreover, the elastic constants of Zr₂Al increase monotonically and the anisotropies decrease with the increasing pressure. Finally, it is observed that Zr d electrons are mainly contributed to the density of states at the Fermi level.     

Lattice stability of Ca, Sr and Yb disilicides

In this paper a study of the lattice stability of Ca, Sr and Yb disilicides is reported. The structural stability of six different prototype lattices was investigated by means of density functional theory calculations and pseudopotentials within the generalized-gradient approximation using the VASP code. The high-pressure equilibria for the CaSi₂ and SrSi₂ have been described deriving the transition pressures, the structural properties, the bulk moduli and the heats of formation for the various polymorphs. Results are discussed together with the experimental literature. For the ytterbium disilicide a specific study of the Si vacancies in the hR3 ground state structure was carried out. Six different supercells derived from the primitive hexagonal cell were considered and full atomic and lattice relaxations were performed in order to predict the energetically most favorable structure. The formation of vacancies in the Si-sublattice is driven by the lowering of the density of states at the Fermi energy. A new mP22 lattice is proposed to describe the structure of the defective YbSi_2 − x phase: the resulting stoichiometry is Yb₄Si₇.     

Half-metallic properties and the robustness of Co2MnGe Heusler alloy under pressure: Ab-initio calculation

To investigate the structural, mechanical, electronic and magnetic properties of full Heusler Co₂MnGe in L2₁ structure, we used first-principle calculations. We made use of all-electron full potential linearized muffin-tin orbital method (FP-LMTO) within the density functional theory. The generalized gradient approximation GGA allows describing the exchange correlation energy. The obtained lattice parameters, bulk modulus and its derivate are in good agreement with experimental and theoretical values. We have also calculated the elastic constants and their related parameters. GGA + U approach allows to process electronic properties. For our compound, the band structure and magnetic moments are treated at equilibrium lattice constant. At Fermi level, the material has a semi metallic behavior with 100% spin polarization ratio. Computed magnetic exchange constants are used to evaluate the Curie temperature from mean field-approximation (MFA). Finally the elastic constants, electronic structure and magnetic properties are investigated at high-pressure. We noticed that half-metal to metal transition was around 102 GPa. The increasing pressure does not affect-the total magnetic moment and the overall shape of the band structure which indicates the robustness of electronic structure of this system.     

First-principles study of electronic structure and magnetic properties of orthorhombic CrGa2Sb2 and MnGa2Sb2

By the first-principles calculations, we present the results of electronic structure and magnetic properties on bulk CrGa₂Sb₂ and MnGa₂Sb₂ in an orthorhombic structure with the linear chains of transition-metal Cr and Mn atoms, using four different exchange correlation potentials: the local density approximation (LDA), the generalized gradient approximation (GGA), GGA + U, and the Tran-Blaha modified Becke-Johnson functional (mBJ). The electronic structure calculations from four exchange correlation potentials show that CrGa₂Sb₂ is a pseudogap (negative gap) material with very small density of states (DOS) at the Fermi level, while MnGa₂Sb₂ has notably higher DOS at the Fermi level compared to CrGa₂Sb₂, exhibiting stronger metallic conductivity, although the mBJ potential obtains lower DOS at the Fermi level than LDA and GGA for both CrGa₂Sb₂ and MnGa₂Sb₂. The GGA + U method with a small value (1 eV) of the on-site Coulomb interaction parameter U obtains lower DOS at the Fermi level compared to the large value of U. In agreement with the measurement data, the total energy calculations reveal that both CrGa₂Sb₂ and MnGa₂Sb₂ have a stable ferromagnetic ground state with lower energies relative to antiferromagnetic state. Based on the Heisenberg model, the magnetic exchange constants between the nearest-neighbor Cr–Cr and Mn–Mn along transition-metal linear chains are calculated to be 48.6 meV and 27.5 meV for CrGa₂Sb₂ and MnGa₂Sb₂, respectively. By the mean-field approximation method, we calculated the Curie temperature of two compounds to be above room-temperature.     

Cr掺杂LiFePO4导电性能的第一原理研究

基于第一原理方法,由广义梯度近似(GGA)的密度泛函理论计算了Cr在Fe位掺杂的LiFePO4的电子结构,分析了不同掺杂量对品胞参数,体积和费米能的影响.掺杂Cr后,系统的态密度图中费米能级移入导带;费米能级附近的价带和导带的峰强度增强;能带结构图中最低空轨道与最高占有轨道之间的能隙变窄,从LiFePO4的0.75 e...     

Mg-Ti-H体系电子结构与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赝势平面波方法,对不同Ti含量的MgxTi(1-x)H2(x=0.25,0.5,0.75,0.875)体系的电子结构进行研究,并预测其光学性质。电子态密度计算结果表明:在MgH2中加入Ti原子,使MgxTi(1-x)H2体系呈现金属特性,这源于Ti诱导费米能级处电子密度增加和费米能级附近能隙消失。电荷密度分析进一步得到了Ti-H原子间形成比Mg–H原子间更强的共价键的成键本质。光学性质预测结果表明,MgxTi(1-x)H2体系中Ti含量对其可见光能量附近的光学性质存在重要影响,较低Ti含量(如Mg0.875Ti0.125H2)不利于提高其可见光的吸收能力,而较高Ti含量(如Mg0.25Ti0.75H2)则对可见光的反射较高。计算结果为制备具有优良的太阳光吸收能力和光电转化效率的Mg-Ti-H光电材料提供了理论依据。     

Structural, electronic and elastic properties of TaRu high temperature shape memory alloys

The structural, electronic and elastic properties of TaRu alloy have been studied by the plane-wave pseudopotential method within the generalized gradient approximation. The crystal structure of the β′ phase is obtained for the first time. Our calculations show that the hybridization between Ta d and Ru d states is responsible for the phase stability of TaRu. The total density of states at the Fermi level of the β′ phase is lower that that of the β phase. In addition, it is found that the β to β′ martensitic transformation is closely related to the elastic properties.     

Cell-structure and mechanical properties of closed-cell aluminum foam

1　INTRODUCTIONMetalfoamsexhibitunusualmechanical,ther mal,acoustic ,damping ,electricalandchemicalprop ertiesthatcannotbefoundinsolidmaterials .Thosespecialpropertiesmayleadtoavarietyofapplicationsinstructuralandfunctionalproducts.Closed cellalu minumfoamisalight massstructuralmaterialofgreatpromise .Itsdensityisonlyafractionofthatofthecorrespondingbulkmetal,butitsstrengthissuf ficientlyhightobeusedintheautomobileindustry ,buildingindustryandtransportation .Examplesoftheirapplicationsinc…     

First principles study on electronic structure and optical properties of novel Na-hP4 high pressure phase

The electronic structure and optical properties of novel Na-hP4 high pressure phase at different pressures (260, 320, 400 and 600 GPa) were investigated by the density functional theory (DFT) with the generalized gradient approximation (GGA) for the exchange and correlation energy. The band structure along the higher symmetry axes in the Brillouin zone, the density of states (DOS) and the partial density of states (PDOS) were presented. The band gap increases and the energy band expands to some extent with the pressure increasing. The dielectric function, reflectivity, energy-loss function, optical absorption coefficient, optical conductivity, refractive index and extinction coefficient were calculated for discussing the optical properties of Na-hP4 high pressure phase at different pressures.     

韧性金属间化合物CeAg的第一性原理计算(英文)

采用第一性原理计算法研究具有B2(CsCl)结构的二元韧性金属间化合物CeAg的结构、力学性能、电子性质以及热力学性能。利用广义梯度近似计算得到的晶格常数为3.713,比自旋密度近似计算的结果更符合实验值。负的形成能表明具有B2结构的CeAg是热力学稳定相。Ce和Ag原子的d能带相互分离导致两者的键合杂化作用较弱,从而阻止具有方向性的共价键形成。计算得到了CeAg的3个独立弹性常数(C11,C12和C44),体模量、剪切模量、弹性模量、各向异性因子以及泊松比分别为57.6GPa、15.8GPa、43.4GPa、3.15和0.374。弹性常数符合所有力学稳定性准则。CeAg的Pugh判据值为3.65,当Pugh判据值大于1.75时,CeAg具有良好的韧性。此外,还计算和讨论了CeAg的体积、体模量、热容和热膨胀系数随温度或者压力的变化规律。     

二维碳材料电子结构与光学性质的第一性原理研究

本文基于密度泛函理论,研究了二维碳材料石墨烯和石墨炔的电子结构和光学性质。计算结果表明石墨烯比石墨炔更稳定,在费米能级附近它们的电子态主要由C-2p态贡献;石墨烯在可见光区域是透明的并且表现出良好的非线性光学吸收特性和电导率;石墨炔的光吸收和光电导对长波下的可见光响应明显,在费米能级附近的电子跃迁,除了从价带到导带的跃迁外还存在带间跃迁。本文的结论可为二维碳材料石墨烯和石墨炔在光电器件、光催化等领域中的应用提供理论依据。     

多元稀土硼化物La1-xEuxB6纳米粉末的制备及光学性能研究

本研究首次采用钙热还原-酸浸法(CTR&AL)成功制备了La_1-xEu_x B₆纳米粉末，研究了Eu掺杂对La_1-xEu_x B₆结构、光学性能的影响规律及作用机理。XRD、FE-SEM及TEM分析结果确认纳米La_1-xEu_x B₆为CsCl型简单立方单相结构，结晶性良好，粉末颗粒具有立方形貌，平均晶粒尺度为40 nm。光吸收结果表明随着Eu含量的增加，纳米La_1-xEu_x B₆透射光波长从595 nm增大至825 nm，产生“红移”现象，且Eu掺杂引起LaB₆近红外区吸收光谱的增强与展宽。第一性原理计算结果揭示了Eu掺杂引起LaB₆近费米能级能带局域性加强，导带中的传导电子数量减少，进而导致其等离激元共振频率能量降低，定性解释了纳米La_1-xEu_...