不同构型下ZnO基稀磁半导体的第一性原理研究

针对5种不同构型下的ZnO基稀磁半导体特性展开研究,利用第一性原理对Co掺杂ZnO,Mn掺杂ZnO,以及(Co,Mn)共掺杂ZnO进行模拟计算,分析其电子结构及磁性。结果表明,Co掺杂ZnO的铁磁性随掺杂位置不同而变化,Mn掺杂ZnO表现出反铁磁性。而(Co,Mn)共掺杂ZnO由于掺杂原子间的相互作用,表现出铁磁性并且具有高于室温的局里温度,是一种理想的稀磁半导体材料。

掺杂半导体β-FeSi_2电子结构及几何结构第一性原理研究

采用基于第一性原理的密度泛函理论全势线性缀加平面波法,使用广义梯度近似处理交换相关势能,首先计算了β-FeSi2的电子结构及其各元素各亚层电子的能态密度,β-FeSi2的电子能态密度主要由Fe的d层电子和Si的p层电子的能态密度确定;其次通过计算不同掺杂系统的总能量确定了掺杂原子在β-FeSi2中的置换位置,在β-FeSi2中,Co置换FeⅡ位置的Fe原子,Al置换SiⅠ位置的Si原子,这种择位置换与现有的计算结果完全一致;最后计算了Fe1-xCoxSi2和Fe(Si1-xAlx)2的电子结构,对它们的电子结构特征进行了分析,并探讨了电子结构对其热电性能(塞贝克系数、电传输及热传输性能)的影响.

在Si(111)面上外延生长的OsSi_2电子结构的研究

采用基于第一性原理的赝势平面波方法,对异质外延关系为OsSi2(101)//Si(111),取向关系为OsSi2[010]//Si<011>的OsSi2平衡体系及附近各点的电子结构进行了理论计算。计算结果表明:当1.005nm≤a≤1.030时,且带隙值随着晶格常数a取值的增大而减小。当a取值为10.20时,体系处于稳定状态,此时OsSi2是具有带隙值为0.628eV的间接带隙半导体。

新型稀磁半导体Mn掺杂LiZnAs的第一性原理研究

采用基于密度泛函理论的第一性原理平面波超软赝势方法,对纯LiZnAs,Mn掺杂的LiZnAs,Li过量和不足下Mn掺杂的LiZnAs体系进行几何结构优化,计算并对比分析了体系的电子结构、半金属性、光学性质及形成能.结果表明新型稀磁半导体Li(Zn0.875Mn0.125)As,Li1.1(Zn0.875Mn0.125)As和Li0.9(Zn0.875Mn0.125)As均表现为100%自旋注入,材料均具有半金属性,Li过量和不足下体系的半金属性明显增强.Li过量可以提高体系的居里温度,改善材料的导电性,使体系的形成能降低.说明LiZnAs半导体可以实现自旋和电荷注入机理的分离,磁性和电性可以分别通过Mn的掺入和Li的含量进行调控.进一步对比分析光学性质发现,低能区的介电函数虚部和复折射率函数明显受到Li的化学计量数的影响.

Rate and Cycling Performance of Ti and Cu Dopedβ-NaMnO_(2) as Cathode of Sodium-ion Battery

Sodium-ion batteries are economical and environmentally sustainable energy storage batteries.Among them,β-NaMnO_(2),a promising sodium-ion cathode material,is a manganese-based oxide with a corrugated laminar structure,which has attracted significant attention due to its structural robustness and relatively high specific capacity.However,it has short cycle life and poor rate capability.To address these issues,Ti atoms,known for enhancing structural stability,and Cu atoms,which facilitate desodiation,were doped intoβ-NaMnO_(2) by first-principles calculation and crystal orbital Hamilton population(COHP)analysis.β-NaMn_(0.8)Ti_(0.1)Cu_(0.1)O_(2) exhibits a notable increase in reversible specific capacity and remarkable rate properties.Operating at a current density of 0.2C(1C=219 mA·g^(–1))and within a voltage range of 1.8–4.0 V,the modified material delivers an initial discharge capacity of 132 mAh·g^(–1).After charge/discharge testing at current densities of 0.2C,0.5C,1C,3C,and 0.2C,the material still maintains a capacity of 110 mA h·g^(–1).The doping of Ti atoms slows down the changes in the crystal structure,resulting in only minimal variation in the lattice constant c/a during the desodiation process.Mn and Cu engage in reversible redox reactions at voltages below 3.0 V and around 3.5 V,respectively.The extended plateau observed in the discharge curve below 3.0 V signifies that Mn significantly contributes to the overall battery capacity.This study provides insights into modifyingβ-NaMnO_(2) as a cathode material,offering experimental evidence and theoretical guidance for enhancing battery performance in Na-ion batteries.

First‑principles study on electronic structure,optical and magnetic properties of rare earth elements X(X=Sc,Y,La,Ce,Eu)doped with two‑dimensional GaSe

The electronic structure,magnetic,and optical properties of two-dimensional(2D)GaSe doped with rare earth elements X(X=Sc,Y,La,Ce,Eu)were calculated using the first-principles plane wave method based on den-sity functional theory.The results show that intrinsic 2D GaSe is a p-type nonmagnetic semiconductor with an indi-rect bandgap of 2.6611 eV.The spin-up and spin-down channels of Sc-,Y-,and La-doped 2D GaSe are symmetric,they are non-magnetic semiconductors.The magnetic moments of Ce-and Eu-doped 2D GaSe are 0.908μ_(B)and 7.163μ_(B),which are magnetic semiconductors.Impurity energy levels appear in both spin-up and spin-down chan-nels of Eu-doped 2D GaSe,which enhances the probability of electron transition.Compared with intrinsic 2D GaSe,the static dielectric constant of the doped 2D GaSe increases,and the polarization ability is strengthened.The ab-sorption spectrum of the doped 2D GaSe shifts in the low-energy direction,and the red-shift phenomenon occurs,which extends the absorption spectral range.The optical reflection coefficient of the doped 2D GaSe is improved in the low energy region,and the improvement of Eu-doped 2D GaSe is the most obvious.

First principles investigation of binary intermetallics in Mg-Al-Ca-Sn alloy:Stability,electronic structures,elastic properties and thermodynamic properties

The structural stability, electronic structures, elastic properties and thermodynamic properties of the main binary phases Mg_（17）Al_（12）, Al_2Ca, Mg_2 Sn and Mg_2 Ca in Mg-Al-Ca-Sn alloy were determined from the first-principles calculation. The calculated lattice parameters are in good agreement with the experimental and literature values. The calculated heats of formation and cohesive energies show that Al_2Ca has the strongest alloying ability and structural stability. The densities of states（DOS）, Mulliken electron occupation number, metallicity and charge density difference of these compounds are given. The elastic constants of Mg_（17）Al_（12）, Al_2Ca, Mg_2 Sn and Mg_2 Ca phases are calculated, and the bulk moduli, shear moduli, elastic moduli and Poisson ratio are derived. The calculations of thermodynamic properties show that the Gibbs free energies of Al_2Ca and Mg_2 Sn are lower than that of Mg_（17）Al_（12）, which indicates that Al_2Ca and Mg_2 Sn are more stable than Mg_（17）Al_（12） phase. Hence, the heat resistance of Mg-Al-based alloys can be improved by adding Ca and Sn additions.

Microstructure of 18R-type long period ordered structure phase in Mg_(97)Y_2Zn_1 alloy

The microstructure of the 18R-type long period stacking ordered （LPSO） phase in Mg 97 Y 2 Zn 1 alloy was investigated by the first principles calculation. The arrangement rule of Zn and Y atoms in the LPSO structure is determined theoretically. The calculation results reveal that the additive atoms are firstly located in the fault layers at the two ends of the 18R-type LPSO structure, and then extend to fault layers in the interior, which is in good agreement with the experimental observations. This feature also implies the microstructural relationship between 18R and other LPSO structures. The cohesive energy and the formation heat indicate the dependence of the stability of 18R LPSO structure on contents of Y and Zn atoms. The calculated electronic structures reveal the underlying mechanism of microstructure and the stability of 18R LPSO structure.

First principles calculation on ternary stannide phase narrow band gap semiconductor Na_2MgSn

The electronic structures,chemical bonding,elastic and optical properties of the ternary stannide phase Na2MgSn were investigated by using density-fimctional 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 Sn5 p 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.

A first-principles study on electronic structure and elastic properties of Al_4Sr, Mg_2Sr and Mg_(23)Sr_6 phases

The electronic structures and mechanical properties of Al4Sr, Mg2Sr and Mg23Sr6 phases were determined by the use of first-principles calculations. The calculated heat of formation and cohesive energy indicate that Al4Sr has the strongest alloying ability as well as the highest structural stability. The elastic parameters were calculated, and then the bulk modulus, shear modulus, elastic modulus and Poisson ratio were derived. The ductility and plasticity were discussed. The results show that Al4Sr and Mg2Sr phases both are ductile, on the contrary, Mg23Sr6 is brittle, and among the three phases, Mg2Sr is a phase with the best plasticity.

First-principles study of phase stability and electronic properties of RhZr

First-principles calculations were carried out to investigate the structural stabilities and electronic properties of RhZr.The plane wave based pseudopotential method was used,in which both the local density approximation（LDA） and the generalized gradient approximation（GGA） implanted in the CASTEP code were employed.The internal positions of atoms in the unit cell were optimized and the ground state properties such as lattice parameter,density of state,cohesive energies and enthalpies of formation of ortho-RhZr and cubic-RhZr were calculated.The calculation results indicate that ortho-RhZr can form more easily than cubic-RhZr and the ortho-RhZr is more stable than cubic-RhZr.The density of states（DOS） reveals that the strong bonding in the Rh-Zr and Rh-Rh or Zr-Zr interaction chains accounts for the structural stability of ortho-RhZr and the hybridization between Rh-4d states and Zr-4d states is strong.

First-Principle Calculation of the Electronic Structure of Sb-Doped SrTiO_3

The electronic structure,including band structure,density of states （DOS）, and partial density of states of SrTi1-xSbxO3 with x = 0,0. 125,0.25,and 0.33 is calculated from the first principles of plane wave ultra-soft pseudo-potential technology based on density function theory. The calculated results reveal that due to the electron doping,the Fermi level moves into the conduction bands for SrTi1-xSbxO3 with x = 0. 125 and the system shows metallic behavior. In addition, the DOS moves towards low energy and the optical band gap is broadened. The wide band gap and the low density of the states in the conduction band result in the transparency of the films.

First principles study of electronic structure, chemical bonding and elastic properties of BiOCuS

The electronic structures, chemical bonding and elastic properties of the tetragonal phase BiOCuS were investigated by using density-functional theory （DFT） within generalized gradient approximation （GGA）. The calculated energy band structures show that the tetragonal phase BiOCuS is an indirect semiconductor with the calculated band gap of about 0.503 eV. The density of states （DOS） and the partial density of states （PDOS） calculations show that the DOS near the Fermi level is mainly from the Cu-3d state. Population analysis suggests that the chemical bonding in BiOCuS has predominantly ionic character with mixed covalent-ionic character. Basic physical properties, such as lattice constant, bulk modulus, shear modulus, elastic constants, were calculated. The elastic modulus and Poisson ratio were also predicted. The results show that tetragonal phase BiOCuS is mechanically stable and behaves in a ductile manner.

Electronic and Optical Properties of O-Terminated Armchair Graphene Nanoribbons

The structure, electromagnetic and optical properties of the O-terminated graphene nanorib- bons with armchair edge are studied using first-principles theory. The results show that the O-terminated armchair edge are more stable than the H-terminated ribbons and show metal- lic character. Spin-polarized calculations reveal that the antiferromagnetic state are more stable than the ferromagnetic state. The energy band and density of states analyses show that the O-terminated armchair edge are antiferromagnetic semiconductors. Because of the terminated 0 atoms, the dielectric function has an evident red shift and the first peak is the strongest with its main contribution derived from the highest valence band. The peaks of the dielectric function, reflection, absorption, energy loss are related to the transition of electrons. Our results suggest that the O-terminated graphene nanoribbons have potential applications in nanoelectronics, opto-electric devices.

First principles calculation of electronic structure, chemical bonding and elastic properties of ultra-incompressible Re_2P

The electronic structures, chemical bonding and elastic properties of the Co2P-type structure phase ultra-incompressible Re2P （orthorhombic phase） were investigated by density-functional theory （DFT） within generalized gradient approximation （GGA）. The calculated energy band structures show that the orthorhombic structure phase Re2P is metallic material. 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 Re-5d state. Population analysis suggests that the chemical bonding in Re2P has predominantly covalent character with mixed covalent-ionic character. Basic physical properties, such as lattice constant, bulk modulus, shear modulus, and elastic constants Cij, were calculated. The elastic modulus and Poisson ratio were also predicted. The results show that the Co2P-type structure phase Re2P is mechanically stable and behaves in a brittle manner.

不同N掺杂硅烯的研究

超级电容器设备是一种通过使用两层不同能量层的存储电极界面,或在内层电极与该材料的外层表面、或者靠近该材料表面之间发生快速而非可逆的氧化和还原化学反应以同时存储一定能量的电子设备。具有多种高能量和低密度磁性电极的量子材料的开发制备应用是当前超级电容器技术研究的一个重点。N原子耦合掺杂技术可有效调节针对硅烯的优化电子存储结构,从而大幅提高针对硅烯的优化量子存储容量并同时改善硅烯电容器的量子能量优化存储。

A first-principles study on interfacial properties of Ni(001)/Ni_3Nb(001)

The Ni （001） surface, Ni3Nb （001） surface and Ni （001）/Ni3Nb （001） interfaces were studied using the first-principles pseudopotential plane-wave method. The adhesion work, thermal stability and electronic structure of Ni/Ni3Nb （001） interfaces were calculated to expound the influence of atom termination and stacking sequence on the interface strength and stability. Simulated results indicate that Ni and Ni3Nb （001） surface models with more than eight atomic layers exhibit bulk-like interior. The （Ni＋Nb）-terminated interface with hollow site stacking has the largest cohesive strength and critical stress for crack propagation and the best thermal stability among the four models. This interfacial Ni and the first nearest neighbor Nb atoms form covalent bonds across the interface region, which are mainly contributed by Nb 4d and Ni 3d valence electrons. By comparison, the thermal stability of Ni/Ni3Nb （001） interfaces is worse than Ni/Ni3A1 （001） interface, implying that the former is harder to form. But the Ni/Ni3Nb interface can improve the mechanical properties ofNi-based superalloys.

First-principles calculation of structural and elastic properties of Pd_(3-x)Rh_xV alloys

The structural stability, electronic and elastic properties of Pd3-xRhxV alloys with L12 and D022 structures were investigated theoretically by the first-principles calculations. The results reveal that with the increase of Rh content, the unit cell volume of Pd3-xRhxV alloys with L12 and D022 structures decreases, and the structure of Pd3-xRhxV alloys tends to transform from D022 to L12. The elastic parameters such as elastic constants, bulk modulus, shear modulus, elastic modulus, and Poisson ratio, were calculated and discussed in details. Electronic structures were also computed to reveal the underlying mechanism for the stability and elastic properties.

一价组胺阳离子结构和性质的计算化学研究

应用第一原理电子结构方法计算了侧链质子化的一价组胺阳离子的各种可能的构象,并且根据所计算的相对吉布斯自由能得到气相和溶液中的最稳定构象.所有的计算结果都表明,无论在气相还是溶液中,g3H构象的相对自由能都是最低,也就是说无论在气相还是溶液中g3H都是最稳定的构象,只不过由于溶剂化作用在水溶液中各个构象之间的自由能差减小,并影响了各个构象在气相和溶液中的相对比率.所得到的这些结构信息对将来计算组胺和各种生物大分子之间的相互作用具有很好的参考价值.

First Principles Study of the Electronic and Magnetic Properties of Ce Doped SrMnO3

The electronic and magnetic properties of Ce doped SrMnO3 have been investigated us- ing the pseudo-potential plane wave method within the generalized gradient approximation method by first principles. The different Mn-O bond lengths indicate that there is a strong Jahn-Teller distortion of the MnO6 octahedron, which associates with a structural phase transition from cubic symmetry （Pm3m） to tetragonal symmetry （I4/mcm）, and the Jahn- Teller ordering stabilizes a chain like （C-type） antiferromagnetie ground state. The electronic structures indicate that SrMnO3 and Sr1-xCexMnO3 （z=0.125 and 0.25） are semiconductor and metallic, respectively. The doping of SrMnO3 with cerium induces simultaneously a decrease in the electrical resistivity, which can be attributed to the formation of Mn3＋ as a result of charge compensation. The density of states and charge density map present that hybridization exists between some of O bands with those of Mn and Ce bands, the bonding between Sr and O is mainly ionic. Density of states and magnetic moment calculations show that the formal valence state of the Ce ion is trivalence.