Mn掺杂Fe2B晶体结构、力学性能及电子结构的第一性原理研究

基于密度泛函理论的第一性原理计算方法,本文系统地研究了Fe8-xMnxB4 (x = 0, 0.25, 0.5, 1, 2, 3, 4, 5, 6, 7 ,8)的晶体结构、机械性能和电子结构。计算得到Fe2B的晶格常数与实验值相符,所有相都具有良好的热力学稳定性和机械稳定性。随着Mn掺杂浓度逐渐增大,Fe8-xMnxB4的各向异性先减弱后增强,Fe7.75Mn0.25B4的各向异性最弱。当Mn掺杂浓度较低时,Fe8-xMnxB4的硬度略微降低,韧性增强。除了Fe7Mn1B4、Fe6Mn2B4、Fe5Mn3B4、Fe4Mn4B4之外,其余的Fe8-xMnxB4相的韧性均比Fe2B好。由电子结构可以发现,Fe8-xMnxB4的力学性能主要由Fe-B键或Mn-B键决定。Mn掺杂到Fe2B中会使得B-B共价键增强,Fe2B的本征脆性得到改善,同时Fe2B的磁性不断减弱。     

Co doping effects on structural, electronic and magnetic properties in Mn2VGa

The electronic structure and magnetic properties of Co-doped Heusler alloys (Mn_1−xCo_x)₂ VGa (x=0.0, 0.25, 0.5, 0.75, 1.0) have been studied by first-principles calculations. The results show that the lattice constants decrease with increasing Co content except x=1.0. The spin polarization for x=0.5 is only 34%, much lower than the other concentrations. The compounds of x=0.0, 0.25 show nearly half-metallicity because the Fermi level slightly touches the valence bands. And the compounds of x=0.75, 1.0 exhibit the half-metallic character with 100% spin polarization. It is found the local moments of Mn(Co) basically show a linear increasing trend while the moments of V show a linear decreasing trend with increasing doping concentration. However, the local moments for x=0.5 quite depart from the linear trend. The majority-spin component at the Fermi level increases while the minority-spin component at the Fermi level decreases with the substitution of Co atoms for Mn atoms when x≤0.75. For x≥0.75, the majority-spin component remains more or less the same and the gap in the minority DOS increases with Co doping. The majority spin states are shifted to valence bands and the majority spin states around E_F increase due to a leakage of charge from the unoccupied spin-up states to the occupied majority states with increasing Co content.     

First-principles study on the electronic structure, magnetic properties and phase stability of alloyed cementite with Cr or Mn

Using the first-principles technique, the electronic structures, magnetic properties and phase stability of alloyed cementite with Cr or Mn were investigated. The calculations show that the chemical and mechanical stability of alloyed cementite can be strengthened by the use of Cr/Mn-doped method. The Magnetic Moments (Ms) of Mn₁Fe₂C, Mn₂Fe₁C, Cr₁Fe₂C and Cr₂Fe₁C are 5.274, 0.941, 1.864 and 0.736 μ_B/f.u, respectively. The Ms of Cr in Fe₂CrC (−1.374 μ_B) and Cr₂FeC (−0.032 μ_B) are different due to replacing different sites Fe atoms. The magnetic behaviors of Mn are different from Cr in alloyed cementite. The Ms of Mn in Fe₂MnC and Mn₂FeC are 2.300 μ_B and −0.147 μ_B, respectively.     

Dangling bond modulating the electronic and magnetic properties of zigzag SiGe nanoribbon

First-principles nonmagnetic calculations reveal a metallic character in zigzag SiGe nanoribbons (ZSiGeNRs) regardless of their width. The partial DOS projected onto the Si and Ge atoms of ZSiGeNR shows that a sharp peak at the Fermi level is derived from the edge Si and Ge atoms. The charge density contours show the Si–Ge bond is covalent bond, while for the Si–H bond and Ge–H bond, the valence charges are strongly accumulated around H atoms due to their stronger 1 s potential and the higher electronegativity of 2.20 than that of 1.90 for Si atom and 2.01 for Ge atom, so that a significant charge transformation from Si or Ge atoms to H atoms and thus an ionic binding feature. Spin–polarization calculations show that the band structures of ZSiGeNR are modified by the dangling bonds. Compared with perfect ZSiGeNR which is a ferrimagnetic semiconductor, the bands of the ZSiGeNRs with bare Si edge, bare Ge edge, and bare Si and Ge edges shift up and nearly flat extra bands appear at the Fermi level. The ZSiGeNR with bare Si edge or bare Ge edge is a ferrimagnetic metal, while ZSiGeNR with bare Si and Ge edges is a nonmagnetic metal.     

Ab initio study of the structural,electronic, elastic and magnetic properties of Cu2GdIn,Ag2GdIn and Au2GdIn

We preformed first-principle calculations for the structural, electronic, elastic and magnetic properties of Cu₂GdIn, Ag₂GdIn and Au₂GdIn using the full-potential linearized augmented plane wave (FP-LAPW) scheme within the generalized gradient approximation by Wu and Cohen (GGA-WC), GGA+U, the local spin density approximation (LSDA) and LSDA+U. The lattice parameters, the bulk modulus and its pressure derivative and the elastic constants were determined. Also, we present the band structures and the densities of states. The electronic structures of the ferromagnetic configuration for Heusler compounds (X₂GdIn) have a metallic character. The magnetic moments were mostly contributed by the rare-earth Gd 4f ion.     

First-principles investigation of structural,elastic, electronic and magnetic properties of Be0.75Co0.25Y (YS,Se and Te) compounds

We have theoretically investigated the structural, elastic, electronic and magnetic properties of Be_0.75Co_0.25Y (YS, Se and Te) alloys, in their zinc-blend phase. This study is carried out by using the full-potential augmented plane wave plus local orbitals method within the density functional theory. Foe computing the exchange-correlation potential, the Wu and Cohen generalized gradient approximation is employed to calculate structural and elastic properties whereas the modified Becke and Johnson potential local density approximation is utilized to examine electronic and magnetic properties. By minimizing the total energy in paramagnetic (PM) and ferromagnetic (FM) phases, it is found the studied compounds are stable in FM structure. The mechanical behavior of the studied compounds is reported with the calculation of shear modulus, Young's modulus, and Poisson's ratio provides. Such mechanical aspects might be useful for the experimentalists to study the mechanical properties upon alloying BeY compounds with Co. We also compute electronic structures, density of states (total and partial), pd-exchange splitting and magnetic moments. Moreover, bond nature is studied by estimating the spin polarized charge densities of Be_0.75Co_0.25Y (YS, Se and Te).     

Structural,electronic, magnetic and vibrational properties of half-Heusler NaZrZ (Z = P,As, Sb) compounds

The structural, electronic, magnetic and vibrational properties of NaZrP, NaZrAs and NaZrSb half-Heusler alloys have been investigated on the basis of density functional theory and generalized gradient approximation. There are three types of structures for these compounds where type a is the most stable one. It is found that all of these materials are half-metallic ferromagnets with a magnetic moment of $2{\mu }_{\mathrm{B}}$. The half-metallic gaps are estimated to be 0.16, 0.35 and 0.55 eV for Z = P, As and Sb, respectively. The hybridization between s and $t_{2g}$ orbitals of Zr with s and p orbitals of Z leads to half-metallic ferromagnetism in these compounds. The effect of strain on the half-metallic property is also investigated, and we notice that the half-metallicity is conserved up to the lattice compressions of 54.43%, 48.29% and 47.55% for NaZrP, NaZrAs and NaZrSb, respectively. The dynamical stability of these compounds is confirmed using dispersion curves. The Curie temperatures are also estimated to be 501.29 K, 855.49 K and 1348.88 K for NaZrP, NaZrAs and NaZrSb, respectively. Therefore, it seems that NaZrZ (Z = P, As, Sb) could be suitable materials for spin-injector applications.     

First-principle study of phase stability,electronic structure and thermodynamic properties of cadmium sulfide under high pressure

By employing first principle and a quasi-harmonic Debye model, we study the phase stability, phase transition, electronic structure and thermodynamic properties of cadmium sulfide (CdS). The results indicate that CdS is a typical ionic crystal and that the zinc-blende phase in CdS is thermodynamically unstable. Moreover, the heat capacity of the wurtzite and rocksalt phases of CdS decreases with pressure and increases with temperature, obeying the rule of the Debye T³ law at low temperature and the Dulong–Petit limit at high temperature.     

First-principle study of the electronic and optical properties of BInGaAs quaternary alloy lattice-matched to GaAs

The first-principle calculations based on density functional theory have been used to study the electronic and optical properties of zinc-blende BInGaAs quaternary alloy lattice-matched to GaAs. The calculated results show the band gap of BInGaAs alloy are direct and the band gap will reduce with the increment of boron and indium composition. The electronic structures of BInGaAs alloy are analyzed via the calculation of density of states. The variation of optical properties including dielectric function, absorption coefficient, reflectivity, refractive index and energy loss function of the alloy were also investigated in detail.     

First-principles study on the influence of biaxial strain on the electronic and magnetic properties of defective blue phosphorene

Regulating the magnetic state of 2D materials is becoming increasingly important for the next generation of spintronic devices. In this study, the first-principles calculation method is used to study the synergistic modulating effect of biaxial strain and vacancy defects on the magnetic properties of blue phosphorene. Results show that only Single Vacancy (SV) doping magnetizes the intrinsic blue phosphorene, Double Vacancy-1 (DV-1), Double Vacancy-2 (DV-2) and Double Vacancy-3 (DV-3) doped blue phosphorene are magnetized under biaxial strain. The magnetic states of SV, DV-1, DV-2 and DV-3 systems change with the intensity of biaxial strain. In some cases, the magnetic moment of the system can be changed from 0 μB to 4 μB. The biaxial strain affects the partially bonding structure near the defects, changes the position of the dangling bond, and thereby adjusts the magnetic state. Our research provides positive guidance for the future application of blue phosphorene in the semiconductor field.     

多壳层铜纳米线结构和电子特性的第一性原理研究

基于密度泛函理论框架下的第一性原理计算,系统地研究了多壳层Cu纳米线的稳定结构和电子特性.得到不同线径多壳层Cu纳米线的平衡态晶格常数相差不大,都表现出金属特性,且其单原子平均结合能和量子电导随着纳米线直径的增加而增加.纳米线中内壳层Cu原子表现出体相结构Cu原子相似的电子特性,而表面壳层由于配位数的减少,其3d态能量范围变窄且整体向费米能级发生移动.电荷密度分析表明,相对于体相Cu晶体中原子间的相互作用,纳米线表面壳层Cu原子与其最近邻原子间的相互作用明显增强.     

A first-principle study of the structural and electronic properties of amorphous Cu-Zr alloys

The atomic and electronic structures of amorphous CuxZr100-x(x=36,46,50,56,64) alloys were simulated using first-principle calculations within a 400-atom supercell.The pair correlation function,coordination numbers,local cluster structures and electronic density of states were analyzed.Reasonable agreements between the theory and the experiments were obtained.The amorphous alloys exhibit different local cluster structures and can all be explained with cluster formulas [cluster](glue)1,3,where the clusters a...     

Structural,electronic and magnetic properties of the double perovskite Pb2FeReO6

The structural, electronic and magnetic properties of the double perovskite Pb₂FeReO₆ have been studied by using the first-principles projector augmented wave (PAW) potential within the generalized gradient approximation (GGA) as well as taking into account the on-site Coulomb repulsive and exchange coupling interactions (GGA+U). The optimized crystal structure of the Pb₂FeReO₆ is a body-centered tetragonal (BCT) with a space group of I4/m and the lattice constants of a=b=5.59 Å and c=7.93 Å, consistent with the experimental results. The two axial transition metal and oxygen (TM–O) distances are slightly larger than the four equatorial TM–O distances and shows the existence of the Jahn–Teller structural distortion in FeO₆ and ReO₆ octahedra. The Fe³⁺ and Re⁵⁺ ions are in the states (3d⁵, S=5/2) and (5d², S=1) with magnetic moments 3.929 and −0.831μ_B respectively and thus antiferromagnetic (AFM) coupling via oxygen between them. The half-metallic (HM) ferromagnetic (FM) nature implies a potential application of this new compound in magnetoelectronic and spintronics devices.     

First-principles study of structural stability, electronic and elastic properties of ZrC compounds

We theoretically study the possible pressure-induced structural phase transition, electronic and elastic properties of ZrC by using first-principles calculations based on density functional theory (DFT), in the presence and absence of spin-orbit coupling (SOC). The calculations indicate that there exists a phase transition from the NaCl-type (B1) structure to CsCl-type (B2) structure at the transition pressure of 313.2 GPa (without SOC) and 303.5 GPa (with SOC). The detailed structural changes during the phase transition were analyzed. The band structure shows that B1-ZrC is metallic. A pseudogap appears around the Fermi level of the total density of states (DOS) of the B1 phase of ZrC, which may contribute to its structural stability.     

Itenerant magnetic properties of amorphous metallic systems: Numerical studies of the Fe-B alloys

A self-consistent method to compute local magnetic moments and spin polarized electron densities of states and to test the stability of the ferromagnetic vs. the paramagnetic state is developed within the framework of the itinerant electron theory. The tight-binding Hamiltonian, with Coulomb correlation among d electrons, is parametrized according to the Slater-Koster interpolation scheme. The method goes beyond the rigid band splitting approximation. We apply it to the Fe_1−xB_x amorphous system for 0 ⩽x⩽0.6 and obtain the magnetization for T=0 as a function of x in agreement with experimental data in the experimentally-accessible concentration region.     

First-principle calculations of structural,electronic and magnetic investigations of Mn2RuGe1-xSnx quaternary Heusler alloys

First-principles calculations were used to calculate the structural, electronic and half-metallic ferromagnetism of Mn₂RuGe_1-xSn_x (x?=?0, 0.25, 0.50, 0.75, 1) Heusler alloys. The Hg₂CuTi-type structure is found to be energetic more than Cu₂MnAl-type structure for both Mn₂RuGe and Mn₂RuSn compounds. The calculated lattice constants for Mn₂RuGe and Mn₂RuSn are 5.91?Å and 6.17?Å, respectively. The electronic band structures and density of states of Mn₂RuGe show a half metallic character with total magnetic moments, 2 μ_B per formula unit that are in good agreement with Slater-Pauling rule with indirect band gap, 0.31?eV along the direction Γ –X. It is observed that the total magnetic moment per cell increases as Sn concentration increases in the Heusler alloys.     

Effect of Ce and Cu co-doping on the structural,morphological, and optical properties of ZnO nanocrystals and first principle investigation of their stability and magnetic properties

Ce, Cu co-doped ZnO (Zn_1−2xCe_xCu_xO: x=0.00, 0.01, 0.02, 0.03, 0.04 and 0.05) nanocrystals were synthesized by a microwave combustion method. These nanocrystals were investigated by using X-ray diffraction (XRD), UV–visible diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM). The stability and magnetic properties of Ce and Cu co-doped ZnO were probed by first principle calculations. XRD results revealed that all the compositions are single crystalline. hexagonal wurtzite structure. The optical band gap of pure ZnO was found to be 3.22 eV, and it decreased from 3.15 to 3.10 eV with an increase in the concentration of Cu and Ce content. The morphologies of Ce and Cu co-doped ZnO samples confirmed the formation of nanocrystals with an average grain size ranging from 70 to 150 nm. The magnetization measurement results affirmed the antiferro and ferromagnetic state for Ce and Cu co-doped ZnO samples and this is in agreement with the first principles theoretical calculations.