A Self-consistent Calculation and an Anisotropic Wavelength Cut off Energy of Spin-wave Spectrumin Magnetic Tunnel Junctions

Temperature dependence of tunnel magnetoresistance (TMR) ratio, resistance, and coercivity from 4.2 K to room temperature (RT), applied de bias voltage dependence of the TMR ratio and resistances at 4.2 K and RT, tunnel current I and dynamic conductance dI/dV as functions of the de bias voltage at 4.2 K, and inelastic electron tunneling (IET) spectroscopy, d(2)I/dV(2) versus V, at 4.2 K for a tunnel junction of Ta(5 nm)/Ni79Fe21(25 nm)/Ir22Mn78(12 nm)/Co75Fe25(4 nm)/Al(0.8 nm)-oxide/Co75Fe25(4 nm)/Ni79Fe21(25 nm)/Ta(5 nm) were systematically investigated. High TMR ratio of 59.2% at 4.2 K and 41.3% at RT were observed for this junction after annealing at 275 degreesC for an hour. The temperature dependence of TMR ratio and resistances from 4.2 to 300 K at 1.0 mV bias and the de bias voltage dependence of TMR ratio at 4.2 K from 0 to 80 mV can be evaluated by a comparison of self-consistent calculations with the experimental data based on the magnon-assisted inelastic excitation model and theory. An anisotropic wavelength cutoff energy of spin-wave spectrum in magnetic tunnel junctions (MTJs) was suggested, which is necessary for self-consistent calculations, based on a series of IET spectra observed in the MTJs.

Self-consistent analysis of double-δ- doped InA1As/InGaAs/InP HEMTs

We have carried out a theoretical study of double-5-doped InAlAs/InGaAs/InP high electron mobility transistor （HEMT） by means of the finite differential method. The electronic states in the quantum well of the HEMT are calculated self-consistently. Instead of boundary conditions, initial conditions are used to solve the Poisson equation. The concentration of two-dimensional electron gas （2DEG） and its distribution in the HEMT have been obtained. By changing the doping density of upper and lower impurity layers we find that the 2DEG concentration confined in the channel is greatly affected by these two doping layers. But the electrons depleted by the Schottky contact are hardly affected by the lower impurity layer. It is only related to the doping density of upper impurity layer. This means that we can deal with the doping concentrations of the two impurity layers and optimize them separately. Considering the sheet concentration and the mobility of the electrons in the channel, the optimized doping densities are found to be 5 × 10^12 and 3× 10^12 cm^-2 for the upper and lower impurity layers, respectively, in the double-5-doped InAlAs/InGaAs/InP HEMTs.

Ab Initio Calculation of Accurate Electronic and Transport Properties of Zinc Blende Gallium Antimonide (zb-GaSb)

This article reports the results of our investigations on electronic and transport properties of zinc blende gallium antimonide (zb-GaSb). Our ab-initio, self-consistent and non-relativistic calculations used a local density approximation potential (LDA) and the linear combination of atomic orbital formalism (LCAO). We have succeeded in performing a generalized minimization of the energy, using the Bagayoko, Zhao and Williams (BZW) method, to reach the ground state of the material while avoiding over-complete basis sets. Consequently, our results have the full physical content of density functional theory (DFT) and agree with available, corresponding experimental data. Using an experimental room temperature lattice constant of 6.09593?, we obtained a direct band gap of 0.751 eV, in good agreement with room temperature measurements. Our results reproduced the experimental locations of the peaks in the total density of valence states as well as the measured electron and hole effective masses. Hence, this work points to the capability of ab-initio DFT calculations to inform and to guide the design and the fabrication of semiconductor based devices—provided a generalized minimization of the energy is performed.

Fully self-consistent calculation ofβ-decay half-lives within Skyrme energy density functional

β-decay half-lives of some magic and semi-magic nuclei have been studied in a fully self-consistent Skyrme Hartree-Fock(HF) plus charge-exchange random phase approximation(RPA).The self-consistency is addressed,in that the same Skyrme energy density functional is adopted in the calculation of ground states and Gamow-Teller excited states.First,the impact of J2 terms on the β-decay half-lives is investigated by using the SGII interaction,revealing a large influence.Subsequently,numerical calculations are performed for the selected nuclei with Skyrme energy density functionals SGII,LNS,SKX,and SAMi.Finally,comparisons to available experimental data and predictions of different theoretical models are discussed.

Simulation of water potential for the electronic structure of serine

First-principles, all-electron, ab initio calculations have been performed to construct an equivalent water potential for the electronic structure of serine （Ser） in solution. The calculation is composed of three steps. The first step is to search for the configuration of the Ser _ nH2O system with a minimum energy. The second step is to calculate the electronic structure of Ser with the water molecule potential via the self-consistent cluster-embedding method （SCCE）, based on the result obtained in the first step. The last step is to calculate the electronic structure of Set with the dipole potential after replacing the water molecules with dipoles. The results show that the occupied states of Ser are raised by about 0.017 Ry on average due to the effect of water. The water effect can be successfully simulated by using the dipole potential. The obtained equivalent potential can be applied directly to the electronic structure calculation of protein in solution by using the SCCE method.

The Magnetic Field Effects on Radially Symmetric Core-Shell-Shell Structure

In this paper, we modeled a core/shell/shell structure with cylindrical Schrodinger-Poisson coupled equation when a magnetic field is (and is not) applied along its axis. We showed the electron density is peaked near the outer surface of the channel when the magnetic field is applied. Therefore one may make a nano-device which its electrons move only on its outer surface. Also we applied a gate voltage to the device and showed a higher threshold voltage (to turn on the device) is necessary when a magnetic field is applied. This is because of the increase in the lowest energy level similar to the size quantization. i.e a device with longer channel looks like a device with shorter channel if it is placed in a magnetic field parallel to its axis.

The equivalent potential of water molecules for electronic structure of lysine

In order to get more reliable electronic structures of proteins in aqueous solution, it is necessary to construct a potential of water molecules for protein’s electronic structure calculation. The lysine is a hydrophilic amino acid. It is positively charged (Lys+) in neutral water solution. The first-principles, all-electron, ab initio calcula-tions, based on the density functional theory, have been performed to construct such an equivalent potential of water molecules for lysine (Lys+). The process consists of three parts. First, the electronic structure of the cluster containing Lys+ and water molecules is calculated. By adjusting the positions of water molecules, the geometric structure of the cluster having minimum total energy is determined. Then, based on the structure, the electronic structure of Lys+ with the potential of water molecules is calculated using the self-consistent cluster-embedding (SCCE) method. Finally, the electronic structure of Lys+ with the potential of dipoles is calculated. The dipoles are adjusted so that the electronic structure of Lys+ with the potential of dipoles is close to that of water molecules. Thus the equivalent potential of water molecules for the electronic structure of lysine is obtained. The major effect of water molecules on lysine’s electronic structure is raising the occupied eigenvalues about 0.5032 eV, and broadening energy gap 89%. The effect of water molecules on the electronic structure of lysine can be simulated by dipoles potential.

Morphological evolution model for unidirectional solidification of multicomponent alloys

Based on the nonlinear interaction of the different species and the calculation of phase diagram,a self-consistent model is developed to describe the interface morphology evolution during unidirectional solidification of multicomponent alloys.This model takes full account of the mutually coupled effect of temperature field,solute field,interface energy and interface attachment kinetics.In comparison with linearization analysis of multicomponent,it not only extends the convergent range of the analysis,but also greatly improves the applicability.

An ab initio study of strained two-dimensional MoSe_2

We have studied the electronic properties of molybdenum diselenide （MoSe2） in both bulk and mono- layer （zigzag and armchair） forms using density function theory. The metallic nature of the zigzag MoSe2 （ZMoSe2） nanoribbon and the semiconducting behavior of the armchair MoSe2 （AMoSe2） nanoribbon have been explored us- ing a band structure calculated using self-consistent calculations. We have also studied the variation in the bandgap in the presence of a small amount of strain （uniaxial, biaxial）. The effect of tensile strain has been investigated and shifts in the conduction band and valance band have been observed with different amounts of applied strain.

Sheet carrier density dependent Rashba spin splitting in the Al_(0.5)Ga_(0.5)N/GaN/Al_(0.5)Ga_(0.5)N quantum well

The Rashba coefficient and Rashba spin splitting for the first subband of the Alo.5Gao.5N/GaN/ Alo.5Gao.5N quantum well （QW） with various sheet carrier densities （Ns） are calculated by solving Schr6dinger and Poisson equations self-consistently. The Rashba spin splitting for the first subband at the Fermi level is considerable and increases evidently with Ns, since the Rashba coefficient, especially the Fermi wave vector increase rapidly. With increasing Ns, the peak of the wave function for the first subband moves towards the left heterointerface, and the average electric field in the well increases, so the two dominant contributions coming from the well and the heterointerface increase. Therefore, the strong polarization electric field and high density of 2DEG in III-nitrides heterostructures are of great importance to a and make the Rashba spin splitting in A1GaN/GaN QWs comparable to that of narrow-gap III-V materials. The results indicate that the sheet carrier density is an important parameter affecting the Rashba coefficient and Rashba spin splitting in A1GaN/GaN QWs, showing the possible application of this material system in spintronic devices.