Enhanced gas-sensing performance of graphene by doping transition metal atoms: A first-principles study

By performing the first-principles calculations, we investigated the sensitivity and selectivity of transitional metal (TM, TMSc, Ti, V, Cr and Mn) atoms doped graphene toward NO molecule. We firstly calculated the atomic structures, electronic structures and magnetic properties of TM-doped graphene, then studied the adsorptions of NO, N₂ and O₂ molecules on the TM-doped graphene. By comparing the change of electrical conductivity and magnetic moments after the adsorption of these molecules, we found that the Sc-, Ti- and Mn-doped graphene are the potential candidates in the applications of gas sensor for detection NO molecule.     

A first-principles study on zigzag phosphorene nanoribbons terminated by transition metal atoms

We have investigated the electronic and magnetic properties of zigzag phosphorene nanoribbons(ZPNRs)with transition metal(TM)passivated atoms,it can be found that the ZPNRs with TM passivated atoms exhibit different magnetisms except for the Ni-passivated system.Meanwhile,the results show that the magnetic moments of ZPNRs with TM passivated atoms are larger than that of ZPNRs with other passivated non-metals/groups.Interestingly,it can be found that Fe-passivated ZPNR exhibits magnetic semiconducting character,which provides the possbility for the application of phosphorene in information storage.For Mn-passivated ZPNRs,it exhibits the half-metallicity.These results may be useful for potential applications of phosphorene in electronic and high-performance spintronic devices.     

Intermediate band insertion by group-IIIA elements alloying in a low cost solar cell absorber CuYSe2: A first-principles study

By using first-principles calculations based on HSE06 hybrid functional, the structural, electronic, and optical properties of CuYSe₂ as a low cost absorber material have been studied. Our results show that CuYSe₂ is a semiconductor with indirect band gap of 1.46 eV and optical band gap of 2.00 eV. Especially, an intermediate band has been found in Ga and In alloyed CuYSe₂, respectively, which can be served as a stepping stone to optical absorption on low energy photons. Therefore, Ga and In alloyed CuYSe₂ with an intermediate band as a new absorber material have been proposed.     

3d过渡金属元素掺杂Al12N12纳米线几何结构和电子性能的第一性原理研究

基于密度泛函理论的第一性原理计算方法,系统地研究了不同3d过渡金属元素(Sc、Ti、V、Cr、Mn、Fe、Co和Ni)掺杂Al₁₂N₁₂纳米线的几何结构、稳定性和电子结构.结果表明：所有掺杂体系均是热力学稳定的;掺杂Ni时体系保留了原有的非磁性间接带隙半导体特性;当掺杂其它原子(Sc、Ti、V、Cr、Mn、Fe、Co)时体系仍然保持为半导体,但带隙明显减小.掺杂过渡金属原子对于Al₁₂N₁₂纳米线的电子结构具有明显的调控作用,在能带调控和光电方面有潜在的应用前景.     

Electronic and magnetic behaviors of graphene with 5d series transition metal atom substitutions: A first-principles study

The electronic structures and magnetic behaviors of graphene with 5d series transition metal atom substitutions are investigated by performing first-principles calculations. All the impurities are tightly bonded to single vacancy in a graphene sheet. The substitutions of La and Ta lead to Fermi level shifting to valence and conduction band, respectively. Both the two substitutions result in metallic properties. Moreover, the Hf, Os and Pt-substituted systems exhibit semiconductor properties, while the Re and Ir-substituted ones exhibit robust half-metallic properties. Interestingly, W-substituted system shows dilute magnetic semiconductor property. On the other hand, the substitution of Ta, W, Re and Ir induce 0.86 μ_B, 2 μ_B, 1 μ_B and 0.99 μ_B magnetic moment, respectively. Our studies demonstrate that the 5d series transition metal substituted graphene have potential applications in nanoelectronics, spintronics and magnetic storage devices.     

Mg12O12纳米线掺杂3过渡金属元素的第一性原理计算研究

基于密度泛函第一性原理计算,系统研究了Mg12O12笼状团簇组装一维纳米线及其掺杂3d族元素体系的几何结构与电子结构。结果表明：Mg12O12团簇组装一维纳米线为非磁性半导体,带隙值为3.16 eV;掺杂Sc和V后,体系由半导体转变为金属;掺杂Ti、Cr、Mn、Fe、Co、Ni、Cu后体系仍然保持半导体特性、但带隙值明显减小,而掺杂Zn时带隙值变化不大;掺杂V、Cr、Mn、Fe、Co、Ni、Cu后纳米线具有磁性。     

Molecular dynamics study of mosaic structure in the Ni-based single-crystal superalloy

The mosaic structure in a Ni-based single-crystal superalloy is simulated by molecular dynamics using a potential employed in a modified analytic embedded atom method. From the calculated results we find that a closed three-dimensional misfit dislocation network, with index of $\langle 011\rangle${\{}100{\}} and the side length of the mesh 89.6\,{\AA}, is formed around a cuboidal $\gamma '$ precipitate. Comparing the simulation results of the different mosaic models, we find that the side length of the mesh only depends on the lattice parameters of the $\gamma $ and $\gamma '$ phases as well as the $\gamma $/$\gamma '$ interface direction, but is independent of the size and number of the cuboidal $\gamma '$ precipitate. The density of dislocations is inversely proportional to the size of the cuboidal $\gamma '$ precipitate, i.e.~the amount of the dislocation is proportional to the total area of the $\gamma $/$\gamma '$ interface, which may be used to explain the relation between the amount of the fine $\gamma '$ particles and the creep rupture life of the superalloy. In addition, the closed three-dimensional networks assembled with the misfit dislocations can play a significant role in improving the mechanical properties of superalloys.     

Ni基金属间化合物第一性原理研究

稀土(R)-过渡族(T)金属间化合物具有优异的物理和化学性质.本研究考虑电子自旋极化作用,基于第一性原理的全电子投影缀加平面波赝势法理论,采用局域自旋密度近似(LSDA),对Ni₁₃Nd₃B₂金属间化合物进行结构优化,计算体系晶格常数、电子结构和磁性能.结果表明,Ni₁₃Nd₃B₂为带隙很小的金属导体.LSDA近似下体系原子间存在复杂作用类型,Nd原子与近邻Ni,B原子以离子键作用为主,Ni原子与近邻Ni原子间表现共价作用情形.体系存在Nd-Ni铁磁耦合,总磁矩约8.4329μB,主要由Nd原子磁矩提供,自旋极化引起的体系Nd-4f,Ni-3p,Nd-5p电子自旋劈裂为体系表现磁性的根本原因.     

Prediction of a bcc-hcp phase transition for Sn: A first-principles study

The high-pressure structural transformation of elemental Sn is studied using an ab initio density functional theory implementation of the metadynamics method that predicts with sufficient compression, Sn will transform from the bcc structure into an hcp structure. The low-free-energy pathway associated with this phase transition is characterized as the Burgers transition mechanism. The superconducting properties of Sn under pressure are also investigated. Both bcc and hcp structures of Sn exhibit very weak electron-phonon coupling and therefore would not sustain superconductivity at high pressure.     

Structural,electronic,and magnetic behaviors of 5d transition metal atom substituted divacancy graphene:A first-principles study

Structural, electronic, and magnetic behaviors of 5d transition metal(TM) atom substituted divacancy(DV) graphene are investigated using first-principles calculations. Different 5d TM atoms(Hf, Ta, W, Re, Os, Ir, and Pt) are embedded in graphene, these impurity atoms replace 2 carbon atoms in the graphene sheet. It is revealed that the charge transfer occurs from 5d TM atoms to the graphene layer. Hf, Ta, and W substituted graphene structures exhibit a finite band gap at high symmetric K-point in their spin up and spin down channels with 0.783 μB, 1.65 μB, and 1.78 μB magnetic moments,respectively. Ir and Pt substituted graphene structures display indirect band gap semiconductor behavior. Interestingly, Os substituted graphene shows direct band gap semiconductor behavior having a band gap of approximately 0.4 e V in their spin up channel with 1.5 μB magnetic moment. Through density of states(DOS) analysis, we can predict that d orbitals of 5d TM atoms could be responsible for introducing ferromagnetism in the graphene layer. We believe that our obtained results provide a new route for potential applications of dilute magnetic semiconductors and half-metals in spintronic devices by employing 5d transition metal atom-doped graphene complexes.     

Unified first-principles study of gilbert damping, spin-flip diffusion, and resistivity in transition metal alloys

Using a formulation of first-principles scattering theory that includes disorder and spin-orbit coupling on an equal footing, we calculate the resistivity ρ, spin-flip diffusion length l(sf), and Gilbert damping parameter α for Ni(1-x)Fe(x) substitutional alloys as a function of x. For the technologically important Ni(80)Fe(20) alloy, Permalloy, we calculate values of ρ = 3.5 ± 0.15 μΩ cm, l(sf) = 5.5 ± 0.3 nm, and α = 0.0046 ± 0.0001 compared to experimental low-temperature values in the range 4.2-4.8 μΩ cm for ρ, 5.0-6.0 nm for l(sf), and 0.004-0.013 for α, indicating that the theoretical formalism captures the most important contributions to these parameters.     

Structural transition of Li3N under high pressure: A first-principles study

We theoretically study the electronic properties and pressure induced solid–solid phase transition of Li₃N by first-principles calculations. The calculations indicate a pressure-induced structural phase transition above 1.5GPa from the ambient $P6/MMM$ hexagonal phase (α-Li₃N) to a layered hexagonal phase (β-Li₃N, P63/MMC) which is accompanied by a 21.6% volume collapse. Above 38.8 GPa, β-Li₃N transforms into γ-Li₃N ($Fm\stackrel{?}{3}m$), and the recently reported new ${\alpha }^{\prime }$-phase ($P\text{-}3M1$) is not stable under high pressure. The analysis of electronic density of states suggests that various Li₃N polymorphs are insulators, and the band gap is broadened with further compression.     

合金元素对Ag/Al界面性质影响的第一性原理研究

采用基于密度泛函理论的第一性原理方法,计算和分析Ag(111)/Al(111)界面体系的能量与电子结构,讨论Ag中加入的Be、Mg、Al、Ca、Ni、Sn合金化元素对Ag/Al界面性质的影响.结果表明:Ni原子倾向于界面处的取代位置,而Be、Mg原子倾向于靠近界面处的取代位置,Al、Ca、Sn原子倾向于远离界面处的取代位置;合金元素Be、Mg、Al、Ca、Ni、Sn的加入均会使Ag/Al界面的稳定性降低,其中Ca元素的影响程度最大,分离功降低到0.923 J/m~2,界面能增至0.703 J/m~2;通过电子结构计算结果分析认为,导致界面稳定性下降的主要原因应是合金化元素的加入使界面间形成的Ag-Al共价键强度降低引起.     

Site preference and elastic properties of ternary alloying additions in B2 YAg alloys by first-principles calculations

First-principles calculations were preformed to study the site preference behavior and elastic properties of 3d (Ti–Cu) transition-metal elements in B2 ductility YAg alloy. In YAg, Ti is found to occupy the Y sublattice whereas V, Cr, Co, Fe, Ni and Cu tend to substitute for Ag sublattice. Due to the addition of 3d transition metals, the lattice parameters of YAg is decreased in the order: V<Cu<Cr<Ni<Co<Fe<Ti. The calculated elastic constants show that Cr, Fe, Co and Cu can improve the ductility of YAg alloy, and Fe is the most effective element to improve the ductility of YAg, while Ti, Ni and V alloying elements can reduce the ductility of YAg alloy, especially, V transforms ductile into brittle for YAg alloy. In addition, both V and Ni alloying elements can increase the hardness of YAg alloy, and Y₈Ag₇V is harder than Y₈Ag₇Ni.     

Electrical conductivity of a non-uniformly deformed metal crystal with alloying elements

The effect is considered of non-uniform deformations satisfying the condition |u ||u |, where is the free path length of an electron in the undeformed crystal and, u is the deformation tensor, on the electrical conductivity of a metal crystal with alloying elements. Account is taken of the local change of the dispersion law for conductivity electrons and also of the dependence on the coordinates of the alloying element of the electron scattering cross-section on the alloying element in the non-uniformly deformed crystal. An explicit expression is obtained for the tensor of the effective conductivity, first introduced by Herring and connecting the average volume density of the electrical current with the average electrical field in the crystal. The local electron scattering cross-section on the charged alloying elements is evaluated on the Thomas-Fermi model taking into account the local change of the constant shielding. Account is also taken of the possibility of redistribution of the alloying elements in the field of the deformations. The dependence is found and discussed of the conductivity on the sign of the constant, introduced in the continuous approximation, of the interaction of the alloying element with the deformation field. By way of illustration of the results obtained the simple case of unidimensional deformation is considered.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 70–75, February, 1973.The writers express their gratitude to Yu. V. Kornyushin for useful discussion of this work.     

Organic/metal interfaces in self-assembled monolayers of conjugated thiols: A first-principles benchmark study

We present an extensive theoretical study of a self-assembled monolayer of a prototype π-conjugated thiol on Au(1 1 1). A series of experimentally accessible quantities are calculated and compared to available experimental data. After assessing the methodology and re-evaluating experimental data in the light of our theoretical results, we focus on the interfacial phenomena determining the modification of the effective workfunction of the substrate and link our findings to the energetic alignment of the frontier molecular orbitals with the metal Fermi level. Since we find no evidence of charge transfer between metal and molecule, the observed interfacial phenomena are rationalized in terms of charge fluctuations and electrostatics at the atomic length scale. The microscopic picture established in this work provides a deeper understanding of the interfacial processes that govern the working principle of single-molecule electronics and organic electronic devices.     

镍基单晶高温合金相界面错配位错网络的演化

运用分子动力学方法,研究了镍基单晶高温合金γ/γ′相界面错配位错网络的特征.通过对界面位错的形成、位错的反应、位错网络的演化等现象的分析发现,在温度场影响下,位错网络将由弛豫初期的十四面体演化成最终的正六面体. 关键词： 镍基单晶高温合金 相界面错配位错 位错网络演化 分子动力学     

A first-principles approach to transition states of diffusion

We propose a first-principles approach for treating the unstable vibrational mode of transition states in solid-state diffusion. It allows one to determine a number of fundamental quantities associated with the transition state, in particular the enthalpy and entropy of migration and the characteristic vibrational frequency, along with their temperature dependences. Application to pure face centered cubic Al shows good agreement with available experimental measurements and previous theoretical calculations. The procedure is further applied in calculations of the migration properties of Mg, Si and Cu impurities in Al, and the differences among Mg, Si and Cu are discussed.     

Study on structure and properties of transition metal doped BiF3 by first-principles

Structure and physical properties of BiF₃ doped with M=Cr, Cu, Fe, Mn, Ni, Ti, V and Co are calculated by the DFT+U method. Effect of metal doping on the electronic structure and optical response of host materials BiF₃ is investigated systematically. New energy levels are formed and located within the band gap, which could decrease the recombination rate of e⁻/h⁺ pairs. Furthermore, transition metal doping extends the optical absorption of BiF₃ to the visible spectral region.     

Site preference of dilute transition metal solutes in Fe3Si

Dilute alloys of the type Fe_3?xT_xSi (0?x?0.2), with T = V, Cr, Mn, Co, Ta, and W, were studied by means of neutron diffraction. The results indicate that V, Cr and Mn have a clear preference for the Fe site with 8 Fe first neighbors, Co for the Fe site with 4 Fe and 4 Si first neighbors, while only tentative conclusions can be drawn for Ta and W.