Electronic structures and magnetic properties of CrSiTe3 single-layer nanoribbons

One-dimensional nanoribbons usually exhibit considerably different properties compared to their monolayer counterparts due to the formation of edge states and limited width. In this study, we systematically investigate the stability, electronic structures and magnetic properties of CrSiTe₃ single-layer nanoribbons with different edge configurations and ribbon widths using first-principles calculations. The results show that the edge energies (less than 0.4 eV/Å) for all studied CrSiTe₃ nanoribbons are much lower than that of graphene and many transition-metal dichalcogenide nanoribbons, indicating their stability and easy formation. Compared to the CrSiTe₃ monolayer with ferromagnetic semiconductor characteristics, some of CrSiTe₃ nanoribbons (N-SiCr-ZNRs, N-Te-ZNRs, N-TeCr-ANRs and N-Te-ANRs) become half-metal due to the hybridization between the d orbitals of edge Cr atoms and the p orbitals of edge Te atoms. While N-SiTe-ANRs are bipolar magnetic semiconductors, in which the states near Fermi level are localized around the nanoribbons edge. Our results show that CrSiTe₃ single-layer nanoribbons are promising candidates suitable for applications in spintronic devices.     

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.     

Orbital-decomposed electronic and magnetic properties of the double perovskite Sr2FeReO6

The detailed orbital-decomposed electronic structures and magnetic properties of the double perovskite Sr₂FeReO₆ have been studied using the first-principles projector augmented wave (PAW) potential within the generalized gradient approximation (GGA). Both occupied and unoccupied s and three p states of Fe³⁺ ion are located far away from the Fermi level, while all up-spin states and most down-spin states are completely filled for the s and three p states of Re⁵⁺ ion. The octahedral crystal field of the oxygen atoms around transition-metal (TM) sites splits the five-fold degenerate d states of the free TM atoms into triply degenerate t_2g states with smaller bonding-antibonding splitting and doubly degenerate e_g states with larger bonding-antibonding splitting. The Fe³⁺ and Re⁵⁺ ions are in the states (3d⁵, S=5/2) and (5d², S=1) with magnetic moments 3.70 and −0.86μ_B, respectively and thus antiferromagnetic coupling via oxygen between them. There are no direct interactions between two nearest Fe-Fe or Re-Re pairs, whereas along each Fe-O-Re-O-Fe or Re-O-Fe-O-Re chains, the hybridizations between Fe 3d and 4s, O 2s and 2p, as well as Re 5p, 5d and 6s orbitals are fairly significant.     

First-principles study of the electronic and magnetic properties of a Nickel-Zinc ferrite: ZnxNi1−xFe2O4

Using first-principles density functional theory within the generalized gradient approximation method, the effect of Zn doping on electronic and magnetic properties of NiFe₂O₄ ferrite spinel has been studied. The crystal structure of the compounds is assigned to a pseudocubic structure and the lattice constant increases as the Zn concentration increases. Our spin-polarized calculations give a half-metallic state for NiFe₂O₄ and a normal metal state for Zn_xNi_1−xFe₂O₄ (0<x≤0.5). Based on the magnetic properties calculations, it is found that the saturation magnetic moment enhances linearly with increase in the Zn content in NiFe₂O₄. The Zn doping in NiFe₂O₄ also induces strong ferrimagnetism since it decreases the magnetic moment of A-sites.     

The electronic and optical properties of Cu doped CdI2

Based on the density functional pseudopotential method, the electronic structures and the optical properties of CdI₂ doped with Cu are investigated in detail. The calculation results indicate that the defect of Cu(Cd) exists steadily with a certain solubility. For the Cu doped CdI₂, the new highly localized impurity bands induced by Cu 3d states lie just across the Fermi energy at the top of the valence band. The doping of Cu induces reduction of band gap of CdI₂; red shifts are revealed in both the imaginary part of dielectric function and the absorption spectra corresponding to the change in band gaps. Moreover, the study of the reflection spectrum and the loss function shows that the doped Cu is responsible for the increased reflection peak intensity and the red shift of the plasma resonant frequency of CdI₂.     

Structural and magnetic properties of MoS2 monolayer zigzag nanoribbon doped by Ti,V, Cr,and Mn

In order to find new functions of monolayer MoS₂ in nanoelectronics or spin electronic devices, using spin-polarized density functional theory (DFT) calculations with on-site coulomb interaction (U), we investigated substitutional doping of Mo atoms of monolayer zigzag MoS₂ nanoribbon (ZZ-MoS₂ NR) by transition metals (TM) (where TM = Ti, V, Cr, Mn) at the Mo-edge, S-edge, and the middle of the NRs. The results of this study indicate the NR widened irrespective of the doped TM position and type, and the Mo-edge was found as the easiest substitutional position. For ZZ-MoS₂ NR doped by Mn, Cr or V atoms, the preferred magnetic coupling state is the edge atoms of S at the S-edge, exhibiting the same spin polarization with TM (named the FM1 state), attributing the NR with metallic magnetism. For Ti-doped monolayer ZZ-MoS₂ NR, in addition to the FM1 state, other preferred magnetic coupling state was observed in which the edge atoms of S at the S-edge exhibit the opposite spin polarization with that of Ti (named the FM2 state). Thus, the NR doped by Ti atom possesses metallic (FM1 state) or half-metallic (FM2 state) magnetism. The total magnetic moments of the ZZ-MoS₂ NR doped by TM follows a linear relationship as a function of the TM dopants (Mn, Cr, V, and Ti). Under $>4\text{\%}$ applied strain, the NR doped by Ti atom only presents the characteristics of half-metallic magnetism as the initial one in the FM2 state, and its total magnetic moment always remained 0 μB, i.e., it was not affected by the width of the NR. This study provides a rational route of tuning the magnetic properties of ZZ-MoS₂ NRs for their promising applications in nanoelectronics and spin electronic devices.     

Electronic structural, elastic properties and thermodynamics of Mg17Al12, Mg2Si and Al2Y phases from first-principles calculations

Electronic structures, elastic properties and thermal stabilities of Mg₁₇Al₁₂, Mg₂Si and Al₂Y have been determined from first-principle calculations. The calculated heats of formation and cohesive energies show that Al₂Y has the strongest alloying ability and structural stability. The brittle behavior and structural stability mechanism is also explained through the electronic structures of these intermetallic compounds. The elastic constants are calculated, the bulk moduli, shear moduli, Young's moduli and Poisson ratio value are derived, the brittleness and plasticity of these phases are discussed. Gibbs free energy, Debye temperature and heat capacity are calculated and discussed.     

过渡金属TM(V,Cr,Mn)掺杂ZnS的电子结构和磁性

采用基于密度泛函理论(DFT)的第一性原理赝势平面波方法,对过渡金属V、Cr、Mn掺杂ZnS的超晶胞体系进行了几何结构优化,计算了晶格常数、电子结构与磁学性质.研究结果表明:掺入V,Cr后,ZnS表现出明显的半金属性,而掺入Mn后,半金属性不明显;掺入过渡金属TM(V,Cr,Mn)后系统产生的磁矩主要有杂质的3d态电子贡献,且磁矩的大小与过渡金属的电子排布有关.     

Structural and Electronic Properties of Li2Mg(NH)2 for Hydrogen Storage: First-principles Study

应用第一原理方法研究了储氢材料α-Li₂Mg(NH)₂和β-Li₂Mg(NH)₂两种构型的结构性质和电子性质．计算优化得到的晶胞参数和N-H键长符合实验得到的数据．通过Murnaghan状态方程得到了体积模量和零压力下的能量,计算结果表明α-Li₂Mg(NH)₂为基态构型．通过Mulliken布居分析说明α构型的N-Li/Mg的离子特性和N-H间的交互作用都弱于β构型．态密度分析结果表明,价带轨道主要由N原子的s轨道和p轨道占据,并与H原子的s轨道杂化．     

First-principles study on electronic structure and elastic properties of Fe16N2

We have performed first-principles study on structural stability, elastic properties and electronic structure of Fe₁₆N₂ by applying LSDA+U method. The calculated values of formation energy and reaction enthalpy for decomposition reaction indicate that Fe₁₆N₂ is a thermodynamically stable phase at the ground state. The six independent elastic constants are derived and the bulk modulus, Young's modulus, shear modulus, and Poisson's ratio are determined as 180 GPa, 199 GPa, 76 GPa and 0.32, respectively. The elastic constants meet all the mechanical stability criteria. The ductility of Fe₁₆N₂ is predicted by Pugh's criterion. The strong bonding between Fe and N atoms results in high values of elastic constants C₁₁ and C₃₃, and contributes to the strengthening of the Fe₁₆N₂ structural stability. The total and partial densities of states (DOS) suggest the existence of hybridization between N-p and Fe-d bands. The position of the Fermi level in DOS curve implies that Fe₁₆N₂ is a metastable phase.     

Electronic structure,optical properties,and phonon transport in Janus monolayer PtSSe via first-principles study

Motivated by the synthesis of a Janus monolayer, the new PtSSe transition-metal dichalcogenide (TMD) have attracted remarkable attention due to their characteristic properties. In this work, we calculated the electronic structure, optical properties, and the thermal conductivity of the PtSSe monolayers, and performed a detailed comparison with other TMDs (monolayer PtS₂ and PtSe₂) using first-principles calculations. The calculated band gaps of the PtS₂, PtSSe, and PtSe₂ monolayers were 1.76, 1.38, and 1.21?eV, respectively, which are in good agreement with experimental data. At the same time, we observed a larger spin-orbit splitting in the electronic structure of PtSSe monolayers. The optical properties were also calculated and a significant red shift was observed from the PtS₂ to PtSSe to PtSe₂ monolayers. The lattice thermal conductivity of the PtSSe monolayer at room temperature (36.19?W/mK) is significantly lower than that of the PtS₂ monolayer (54.25?W/mK) and higher than that of the PtSe₂ monolayer (18.07?W/mK). Our results show that the PtSSe monolayer breaks structural symmetry and has the same ability to reduce the thermal conductivity as MoSSe and ZrSSe monolayers due to the shorter group velocity and the lower converged phonon scattering rate. These results may stimulate further studies on the electronic structure, optical properties, and thermal conductivity of the PtSSe monolayer in both experimental synthesis and theoretical efforts.     

First-principles study of the structural, magnetic, and electronic properties of LiMBO3 (M = Mn, Fe, Co)

We present a first-principles calculation for the structural, magnetic, and electronic properties of LiMBO₃ (M = Mn, Fe, Co). Along the [0 0 1] direction, transition metals shows antiferromagnetic coupling in LiMBO₃ of both hexagonal and monoclinic lattices. The calculated magnetic moment of 5μB per formula unit is close to the experimental value. These compounds are semiconductors with band gap of 0.4-2 eV, and with average intercalation voltages of 2-4.8 V.     

Spin-orbital coupling and magnetic properties of Ir-based double perovskites with different 5dn (n = 3, 4, 5) states

We have investigated the spin and orbital moments of Ir-based double perovskites with $5d^n$ (n = 3, 4, 5) states by local spin-density approximation with spin-orbital coupling and Hubbard correlation (LSDA+SOC+U). Our calculations reveal that the ratio of orbital to spin momentum $L_z/S_z$ approaches to certain values for the double perovskites with different 5dⁿ (n = 3, 4, 5) shell fillings. Based on d orbits, a spin-orbital coupling model with exchange splitting is proposed and it can well describe the ratio of angular momentums for the compounds. Our model calculations reveal that $L_z/S_z$ is determined by the exchange splitting, spin-orbital coupling as well as the state of shell filling. Our model is well corroborated by the experiments and density-functional calculations.     

Electronic structural properties and formation energy of Sn1−xPbxO2 solid solutions electrode

First-principles calculations based on density functional theory within the generalized gradient approximation have been performed for the Sn_1−xPb_xO₂ solid solution. The doped formation energies and electronic structures are also analyzed. Results show that the Sn_0.9375Pb_0.0625O₂ solid solution has the highest stability because of its minimum formation energy value of 0.04589 eV at a doping ratio of 0.0625. The SnO₂ lattice constants expand in a distorted rutile structure after Pb doping. The band structure and density of states calculations indicate that the band gap of SnO₂ narrowed due to the presence of the Pb impurity energy levels in the forbidden band, namely, Pb 6s energy band overlaps with the conductivity band in the F–Q direction. In addition, the number of electrons filled at the bottom of the conduction band increases from 0.13 to 3.96 after doping, resulting in the strengthening of the conductivity of the solid solution after doping of plumbum. The results provide a theoretical basis for the development and application of the Sn_1−xPb_xO₂ solid solution electrode.     

Electronic structure and magnetic properties of BaTi1-xMnxO3

The electronic structure and magnetic properties of polycrystalline BaTi_1-xMn_xO₃ (x = 0–0.1) compounds prepared by solid-state reactions were studied. The results revealed that the increase in Mn content (x) did not change the oxidation numbers of Ba (+2) and Ti (+4) in BaTi_1-xMn_xO₃. However, there is the change in Mn valence that Mn^3+,4+ ions coexist in the samples with x = 0.01–0.04 while Mn⁴⁺ ions are almost dominant in the samples with x = 0.06–0.1. We also point out that Mn³⁺ and Mn⁴⁺ ions substitute for Ti⁴⁺ and prefer locating in the tetragonal and hexagonal BaTiO₃ structures, respectively, in which the hexagonal phase constitutes soon as x = 0.01. Particularly, all the samples exhibit room-temperature ferromagnetism. Ferromagnetic order increases with increasing x from 0 to 0.02, but decreases as x ≥ 0.04. We think that ferromagnetism in BaTi_1-xMn_xO₃ is related to lattice defects and/or exchange interactions between Mn³⁺ and Mn⁴⁺ ions.     

Piezoelectric, dielectric and magnetic properties of (1-x)Pb[Zr, Ti, (Mg1/2W1/2), (Ni1/3Nb2/3)]O3+x(Ni, Co, Cu)FeO4 composites

The phase structure, microstructure, piezoelectric properties, dielectric characteristic and the ME effect of magnetoelectric Pb[Zr_0.23Ti_0.36+0.02(Mg_1/2W_1/2)+0.39(Ni_1/3Nb_2/3)]O₃ (PZT)+xNi_0.8Co_0.1Cu_0.1Fe₂O₄ (NCCF) composite ceramics were prepared by the conventional solid state reaction method. The structural analysis of both the constituent phases and their composites was carried out by X-ray diffraction, energy dispersive spectrometry and scanning electron microscopy. The results showed cubic spinel structure for ferrite phase and tetragonal perovskite structure for ferroelectric phase. The piezoelectric constant, dielectric constant, Curie temperature, remanent polarization and coercive electric field decreased with increase of ferrite content. The coercive field strength, saturation magnetization and remanent magnetization increased with increasing ferrite content.     

The mechanical,thermodynamic and electronic properties of Al3Nb with DO22 structure: A first-principles study

The lattice constants, elastic properties, electronic structure and thermodynamic properties of Al₃Nb with DO₂₂ structure have been investigated by the first-principles calculation. The calculated lattice constants were consistent with the experimental values, and the structural stability was also studied from the energetic point of view. The single-crystal elastic constants (C_ij) as well as polycrystalline elastic parameters (bulk modulus B, shear modulus G, Young's modulus E, Poisson's ratio υ and anisotropy value A) were calculated, and brittleness of Al₃Nb was discussed in detail. Besides, the electronic structure of tetragonal Al₃Nb was studied, which indicates a mixture of metallic bond and covalent bond in Al₃Nb and reveals the underlying mechanism of the stability and elastic properties of Al₃Nb. Finally, the thermodynamic properties of Al₃Nb were calculated and the physical properties such as heat capacity and Debye temperature were predicted within the quasi-harmonic approximation.     

Electronic structures of zigzag AlN, GaN nanoribbons and AlxGa1−xN nanoribbon heterojunctions: First-principles study

The electronic and structural properties of zigzag aluminum nitride (AlN), gallium nitride (GaN) nanoribbons and Al_xGa_1−xN nanoribbon heterojunctions are investigated using the first-principles calculations. Both AlN and GaN ribbons are found to be semiconductor with an indirect band gap, which decreases monotonically with the increased ribbon width, and approaching to the gaps of their infinite two dimensional graphitic-like monolayer structures, respectively. Furthermore, the band gap of Al_xGa_1−xN nanoribbon heterojunctions is closely related to Al (and/or Ga) concentrations. The Al_xGa_1−xN nanoribbon of width n=8 shows a continuously band gap varying from about 2.2 eV-3.1 eV as x increases from 0 to 1. The large ranged tunable band gaps in such a quasi one dimension structure may open up new opportunities for these AlN/GaN based materials in future optoelectronic devices.     

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.