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Degenerate semiconductor is very highly desired in energy conversion and storage technologies due to its metal-like conduction behaviors. This is the first time the doping S2 in Ni3S2 lattice into chemically homogeneous Ni3(S)1.1(S2)0.9 superlattice structure is proposed to induce a degenerate characteristic towards excellent electrical conductivity and high-rate capability. In this study, a series of the chemically homogeneous S2-doped Ni3(S)1.8(S2)0.2, Ni3(S)1.6(S2)0.4, Ni3(S)1.3(S2)0.7, and Ni3(S)1.1(S2)0.9 micropyramid arrays on Ni foam were synthesized by reacting the Ni foam and alkaline sulfur aqueous solution in different S22- concentrations. The perfect Ni3(S)1.1(S2)0.9 superlattice structure corresponds to the periodic S–Ni–S2 atom arrangements in whole crystal lattice, which endows a degenerate characteristic of metal-like electrical conductivity to significantly improve the electrochemical performance. The bulk series resistance (Rs) value is only 0.62 Ω, while the charge-transfer resistance (Rct) is nearly 0 Ω in the superlattice Ni3(S)1.1(S2)0.9 electrode. As a cathode material for application in lithium ion batteries (LIBs), a very high specific capacity of 874 mAh g−1 is achieved at current density of 200 mA g−1. Remarkably, it still holds a high capacity of 565 mAh g−1 at current density of 500 mA g−1, indicating its superior high-rate capability. This study reveals that the periodic S–Ni–S2 atom arrangements in crystal lattice is a key factor in determining the superlattice structure, high specific capacity, and the dynamic behaviors of electron/ion transport.

Can aluminum generate deformation twins? Contradictories exist among the experimental results, theoretical predictions, and molecular dynamics simulations. Our first-principles calculations based on the full-potential linearly augmented plane wave method show that the bonding electron density of aluminum gathers at the tetrahedral interstices, and this specific electronic structure is in agreement with the experimental data from quantitative convergent-beam electron diffraction. In terms of this characteristic, the matching between the cohesive energy of local deformation twins with different thickness and global matrix can shed light on deformation twins in aluminum. This study may give a lane to insight into deformation twins in different metals.

It is difficult to build the constitutive equations for macroscopic magnetoelastic behavior because the coupling is a very complex phenomenon. Progress has been recently made in the description of the magnetoelastic behavior of single crystals. The objective of this paper is to propose a homogenization approach to predict the macroscopic magnetoelastic behavior for magnetic polycrystals, which is extended from the description of the single crystal behavior. The model remains connected to microscale physics, which efficiently reproduce macroscale behavior. This kind of micro–macro strategy could then participate in the understanding of the effect of stress on the magnetic behavior, especially in the case of multiaxial loadings.

The electronic and structural properties of δ-Pu and PuO have been investigated by means of the density functional theory using the full-potential linearized augmented plane wave (FLAPW) method and the local spin density approximation (or the generalized gradient approximation) with on-site Coulomb repulsion U (LSDA/GGA+U) method. The results of our calculations show that by calculating an appropriate U, it is promising to correctly and consistently describe structural and electronic properties of δ-Pu and PuO. The results for δ-Pu indicate that calculated lattice parameters and elastic constants are in good agreement with the corresponding experimental data. From the present calculation we also predict the lattice parameters and elastic constants for PuO, which were not observed in previous experiments. In particular, we demonstrate that the localization effect of the 5f electrons is stronger than itinerancy to elemental plutonium, and predict the existence of a quasiparticle-like peak near the Fermi level and give an appropriate viewpoint on the physics of plutonium.

We have performed ab initio calculations of the structural, dielectric, and lattice-dynamical properties of the zinc-blende ZnX (X = O, S, Se, Te) using a plane-wave pseudopotential method within the density-functional theory. A linear-response approach to the density-functional theory as implemented in the code ABINIT is used to calculate the Born effective charges, electronic dielectric tensors, phonon frequencies and LO–TO splitting. Compared to the direct approach (or frozen-phonon approach), the linear-response approach has important advantages in that time-consuming supercell calculations are avoided and phonons of arbitrary wave vector can be treated with a cost that is independent of wave vector. The calculated bulk lattice constant values of 4.616 A, 5.392 A, 5.674 A, and 6.226 A for ZnO, ZnS, ZnSe and ZnTe, respectively, were used for phonon calculations. The LO–TO splitting frequencies (in cm−1) at the zone-center (Γ point) are ZnO: LO = 517, TO = 367; ZnS: LO = 333, TO = 267; ZnSe: LO = 245, 205; ZnTe: LO = 188, TO = 161. The computed values are in reasonable agreement with experimental data and other calculations.

The ground-state properties of NiO have been investigated using the all-electron full-potential linearized augmented plane wave (FLAPW) and the so-called LSDA (GGA)+ U (LSDA—local-spin-density approximation; GGA—generalized gradient approximation) method. The calculated result indicates that our estimation of U is in good agreement with experimental data. It is also found that none of the LSDA (GGA) methods is able to provide, at the same time, accurate electronic and structural properties of NiO. Although the GGA+ U method can properly predict the electronic band gap, it overestimates the lattice constant and underestimates the bulk modulus. Then only the LSDA+ U method accurately reports the electronic and structural properties of NiO. The calculated band gap and the density of states (DOS) show that the material NiO is the charge-transfer insulator, which agrees with the spectroscopy data. The comparison between the charge density of LSDA (not considering U ) and that of LSDA+ U (considering U ) demonstrates that the trend of ionic crystal for NiO is obvious.

The structure properties of LaNi3.5Al1.5 have been investigated by the density functional theory using the full-potential linearized augmented plane wave (FLAPW) method with the generalized gradient approximation (GGA). The elastic constants of LaNi3.5Al1.5 are determined by a least-squares fitting of the calculated binding energy with a generalized two dimensional cubic function of lattice parameter a and c . The results show that the calculated lattice parameters ( a = b = 0.5092 nm and c = 0.4214 nm) are in good agreement with the corresponding experimental data, that Al atoms prefer to substitute Ni atoms in the 3g sites and tend to disperse in middle planes. For LaNi3.5Al1.5, the bulk modulus (123.1 GPa), the shear modulus (68.6 GPa) and the values of the elastic constants C11+C12 (296.2 GPa), C13 (76.4 GPa) and C33 (210.5 GPa) are worked out for the first time. The ratio of c/a tends to increase from 0.790 (LaNi5) to 0.804 (LaNi4Al) and 0.827 (LaNi3.5Al1.5), which indicates that the LaNi3.5Al1.5 compound is observed to change less anisotropic with the substitution of Al atoms than the host alloy.

For the generalized statistical mechanics based on the Tsallis entropy, a variational perturbation approximation method with the principle of minimal sensitivity is developed by calculating the generalized free energy up to the third order in variational perturbation expansion. The approximation up to the first order amounts to a variational approach which covers the variational method developed by E.K. Lenzi, L.C. Malacarne, R.S. Mendes [Phys. Rev. Lett. 80 (1998) 218] and the approximations up to higher orders can systematically improve variational results. As an illustrated example, the generalized free energy for a classical harmonic oscillator (considered in the Lenzi's joint work) are calculated up to the third order, and the resultant approximations up to the first, second, and third orders are numerically compared with the exact result.

We propose a scheme for the effective polarization and manipulation of electron spin by using a quantum dot with both charge and spin bias. Using the equation of motion for Keldysh nonequilibrium Green function, we study the spin accumulation and polarization for the system. Through analytical analysis and a few numerical examples, it is demonstrated that fairly large spin accumulation and polarization can be produced due to the breaking symmetry of the chemical potential for different electron spin in the leads. Moreover, the direction and the strength of the spin polarization can be conveniently controlled and tuned by varying the charge bias or the gate voltage.

We have performed ab initio calculations of the structural, dielectric, and lattice-dynamical properties of the zinc-blende ZnX (X = O, S, Se, Te) using a plane-wave pseudopotential method within the density-functional theory. A linear-response approach to the density-functional theory as implemented in the code ABINIT is used to calculate the Born effective charges, electronic dielectric tensors, phonon frequencies and LO–TO splitting. Compared to the direct approach (or frozen-phonon approach), the linear-response approach has important advantages in that time-consuming supercell calculations are avoided and phonons of arbitrary wave vector can be treated with a cost that is independent of wave vector. The calculated bulk lattice constant values of 4.616 A, 5.392 A, 5.674 A, and 6.226 A for ZnO, ZnS, ZnSe and ZnTe, respectively, were used for phonon calculations. The LO–TO splitting frequencies (in cm−1) at the zone-center (Γ point) are ZnO: LO = 517, TO = 367; ZnS: LO = 333, TO = 267; ZnSe: LO = 245, 205; ZnTe: LO = 188, TO = 161. The computed values are in reasonable agreement with experimental data and other calculations.

We study the spin-dependent electron transport in an armchair graphene nanoribbon sample driven by both the charge and the spin biases within the tight-binding framework. By numerical calculations we give the spin-dependent currents for a fixed spin bias as a function of the charge bias. It is found that we can let only one type of spin current pass through the graphene nanoribbon for a wide range of charge bias, which is due to the difference of the bias voltage windows for different spin electrons when the charge and the spin biases coexist. Moreover, the pure spin current can be controlled via the charge bias. Our results are suggestive for developing new kinds of spin filters.