Electron Exchange-correlation Potential Research Articles

Review of electron emission and electrical breakdown in nanogaps

With the continual miniaturization of electronic devices, there is an urgent need to understand the electron emission and the mechanism of electrical breakdown at nanoscale. For a nanogap, the complete process of the electrical breakdown includes the nano-protrusion growth, electron emission and thermal runaway of the nano-protrusion, and plasma formation. This review summarizes recent theories, experiments, and advanced atomistic simulation related to this breakdown process. First, the electron emission mechanisms in nanogaps and their transitions between different mechanisms are emphatically discussed, such as the effects of image potential (of different electrode's configurations), anode screening, electron space-charge potential, and electron exchange-correlation potential. The corresponding experimental results on electron emission and electrical breakdown are discussed for fixed nanogaps on substrate and adjustable nanogaps, including space-charge effects, electrode deformation, and electrical breakdown characteristics. Advanced atomistic simulations about the nano-protrusion growth and the nanoelectrode or nano-protrusion thermal runaway under high electric field are discussed. Finally, we conclude and outline the key challenges for and perspectives on future theoretical, experimental, and atomistic simulation studies of nanoscale electrical breakdown processes.

Stopping Power Modulation by Pump Waves of Charged Particles Moving above Two-Dimensional Electron Gases

The perturbation electron density and stopping power caused by the movement of charged particles above two-dimensional quantum electron gases (2DQEG) have been studied in numerous works using the quantum hydrodynamic (QHD) theory. In this paper, the QHD is modified by introducing the two-dimensional electron exchange-correlation potential at high density Vxc2DH and the pump wave modulations. Based on the modified QHD, the perturbation electron density and stopping power are calculated for pump waves with various parameters. The results show that the stopping power values are more accurate after considering Vxc2DH. Under the modulation of pump waves with the wavelength from 0.1nm to 0.1cm, the perturbation electron density of 2DQEG and the stopping power of charged particles show periodic changes. Under the modulation of pump waves with λ = 1.76 × 10−4 cm and Φ0=2×1010e/λf, the average stopping power with respect to the time phase θ becomes negative, which means that the charged particles will gain energy and can be accelerated. This is a new phenomenon in the fields of 2DQEG and of great significance in surface physics and surface modification in nanoelectronic devices with beam matter interactions.

Half-metallic ferromagnetism study of quaternary fluoro-elpasolite Rb2NaCrF6

In this work, we have predicted the structural, electronic, and magnetic properties of the quaternary fluoro-elpasolite Rb2NaCrF6 alloy. We have performed our calculations by the use of first-principle methods developed on spin-polarized density functional theory, where the electronic exchange–correlation potential is evaluated by the generalized gradient approximation GGA-PBEsol coupled with the improved TB-mBJ approach. The calculated structural parameters of Rb2NaCrF6 are in good agreement with the available experimental data. Rb2NaCrF6 exhibits a half-metallic ferromagnetic feature with a spin polarization of 100% at the Fermi level and a direct large half-metallic gap of 2.04 eV. The total magnetic moments are 3μB. This compound is half-metallic ferromagnets, and it can be potential candidates for spintronics applications at a higher temperature.

Nonlinear dissipative wave structures in planar and nonplanar geometry with quantum electron exchange-correlation potential

Taking into account the effects of electron exchange-correlation potential, particle collisions, the nonlinear dynamical properties of planar and nonplanar (cylindrical and spherical) electrostatic ion-acoustic waves (IAWs) are investigated theoretically and numerically in quantum plasmas. With the aid of quantum hydrodynamic model and the reductive perturbation technique, the planar and nonplanar dispersive-dissipative equations (modified Kakutani–Kawahara equations) are obtained to elucidate the nonlinear quantum IAW profiles. The influences of the electron exchange-correlation potential, Bohm potential and collisional effects in the wave dynamics are studied. For a typical parametric range, relevant for laboratory and astrophysical environments, it is found that the contribution from exchange-correlation potential to be prominent in comparison to the effect due to the Bohm potential. Also, numerical simulation predicts that the dissipation induced by the particle collisions leads to the evolution of low frequency shock structures in dense quantum plasmas.

Spinelectronic investigation of the quaternary vanadium fluoride Rb2NaVF6: Ab-initio method

In this study, we have investigated the structural, electronic, and magnetic properties of the Rb2NaVF6 compound. We have performed our calculations by the use of first-principle methods based on spin-polarized density functional theory, where the electronic exchange-correlation potential is treated by the generalized gradient approximation GGA- PBEsol coupled with the improved TB-mBJ approach. The calculated structural parameters of Rb2NaVF6 are in good agreement with the available experimental data. Rb2NaVF6 exhibits a half-metallic ferromagnetic feature with a spin polarization of 100 % at the Fermi level and a direct large half-metallic gap of 3.582 eV. The total magnetic moments are 2 μB. This material is half-metallic ferromagnets, and it can be potential candidates for spintronics applications at a higher temperature.

On a semiclassical model for damped dust ion-acoustic solitons with analysis of quantum electron exchange-correlation potential

The semiclassical hydrodynamic model is used to study the effect of electron exchange-correlation potential, quantum Bohm term, and degenerate pressure on the dynamics of dust ion acoustic waves by following the two-fluid theory in collisional, unmagnetized dusty plasma. For linear analysis, the dispersion relation modified by the exchange-correlation coefficient is derived. For nonlinear analysis, the standard perturbative approach is used to derive a deformed Korteweg–deVries equation with a linear damping term for finite amplitude waves. The analytical and numerical investigations in the presence of low collisional frequencies reveal the existence of compressive dissipative solitons. Considering the dense astrophysical objects, the dissipative compressive solitons are numerically investigated with the effect of different plasma parameters including collisions and exchange-correlation potential.

The effect of substitution of Cr impurities at the In sites on the structural, electronic and magnetic properties of InSb: a DFT study within mBJ potential

In this work, we have investigated the structural, electronic and magnetic properties of In1 − xCrxSb alloys in zinc blende at concentrations x = 0.125, 0.25, 0.50, 0.75, 0.875 and 1. We have performed our calculations by the use of first-principle methods based on spin-polarized density functional theory, where the electronic exchange–correlation potential is treated by the generalized gradient approximation GGA-WC and the improved TB-mBJ approach. The calculated structural parameters of InSb are in good agreement with the available theoretical and experimental data. The ternary In1 − xCrxSb alloys show half-metallic ferromagnetic behavior with a spin polarization of 100% at the Fermi level. The total magnetic moments are 3 μB for all compounds and the interaction is antiferromagnetic between Cr–Sb and Sb–In sites. These materials are half-metallic ferromagnets, and they can be potential candidates for spintronic applications.

First-principles investigation of electronic structure and derived structural and magnetic properties of HgTe alloyed with Mn transition metal

Full potential linearized augmented plane wave calculations for the entire range of alloy concentrations of cubic Hg1-xMnxTe are reported. The electronic exchange-correlation potential has been treated using the generalized gradient approximation (GGA). For high accuracy of band-gap energies, we used also the modified Becke-Johnson exchange potential with the GGA. Our results are generally in reasonably good accord with data available from the literature. It is found that the lattice parameter of the material system of interest violates Vegard's law. By alloying HgTe with various concentrations of Mn transition metal, Hg1-xMnxTe becomes less compressible and the total magnetic moment becomes more important. The analyses of the electronic structure and density of states showed that the alloy system in question exhibits a semiconducting character. The chemical trends of the material under investigation are examined and discussed from an aspect of electronic charge densities. The information obtained in the present study could become good guidance for use of this alloy system in various device applications, e.g., in photoconductive detector applications.

Theoretical investigation of the structural stabilities, optoelectronic properties and thermodynamic characteristics of GaPxSb1−x ternary alloys

In this theoretical study, we have investigated the structural, phase transition, electronic, thermodynamic and optical properties of GaPxSb1−x ternary alloys. Our calculations are performed with the WIEN2k code based on density functional theory using the full-potential linearized augmented plane wave method. For the electron exchange-correlation potential, a generalized gradient approximation within Wu–Cohen scheme is considered. The recently developed Tran–Blaha modified Becke–Johnson potential has also been used to improve the underestimated band gap. The structural properties, including the lattice constants, the bulk moduli and their pressure derivatives are in very good agreement with the available experimental data and theoretical results. Several structural phase transitions were studied here to establish the stable structure and to predict the phase transition under hydrostatic pressure. The computed transition pressure (Pt) of the material of our interest from the zinc blende (B3) to the rock salt (B1) phase has been determined and found to agree well with the experimental and theoretical data. The calculated band structure shows that GaSb binary compound and the ternary alloys are direct band gap semiconductors. Optical parameters such as the dielectric constants and the refractive indices are calculated and analyzed. The thermodynamic results are also interpreted and analyzed.

Erratum: “Effects of electron exchange-correlation potential on electrostatic oscillations in single-walled carbon nanotubes” [J. Appl. Phys. 115, 204304 (2014)

Erratum: “Effects of electron exchange-correlation potential on electrostatic oscillations in single-walled carbon nanotubes” [J. Appl. Phys. <b>115</b>, 204304 (2014)

Comment on “Effects of electron exchange-correlation potential on electrostatic oscillations in single-walled carbon nanotubes” [J. Appl. Phys. 115, 204304 (2014)

In a recent article, Khan and Hassan [J. Appl. Phys. 115, 204304 (2014)] investigated the dispersion properties of electrostatic electron plasma oscillations on the surface of single-walled carbon nanotubes by considering the exchange-correlation potential. They showed that the surface plasmon energies are blue-shifted by the exchange-correlation effects. Here, we derive the correct form of the dispersion relation and show that the energies of plasmonic modes are red-shifted by the exchange-correlation effects.

First-principles calculations of a half-metallic ferromagnet zinc blende Zn 1−x V x Te

Abstract First-principles calculations have been used to study the structural, elastic, electronic, magnetic and thermal properties of zinc blende Zn1−xVxTe for x=0, 0.25, 0.50, 0.75 and 1 using the full-potential linearized augmented plane wave method (FP-LAPW) based on spin-polarized density functional theory (DFT). The electronic exchange-correlation potential is approached using the spin generalized gradient approximation (spin-GGA). The structural properties of the Zn1−xVxTe alloys (x=0, 0.25, 0.50, 0.75 and 1) are given for the lattice constants and the bulk moduli and their pressure derivatives. The elastic constants C11, C12 and C44 are calculated using numerical first-principles calculations implemented in the WIEN2k package. An analysis of the band structures and the densities of states reveals that Zn0.50V0.50Te and Zn0.75V0.25Te exhibit a half-metallic character, while Zn0.25V0.75Te is nearly half-metallic. The band structure calculations are used to estimate the spin-polarized splitting energies Δx(d) and Δx(pd) produced by the V(3d)-doped and s(p)–d exchange constants N0α (conduction band) and N0β (valence band). The p–d hybridization reduces the magnetic moment of V from its atomic charge value of 3µB and creates small local magnetic moments on the nonmagnetic Zn and Te sites. Finally, we present the thermal effect on the macroscopic properties of these alloys, such as the thermal expansion coefficient, heat capacity and Debye temperature, based on the quasi-harmonic Debye model.

Effects of electron exchange-correlation potential on electrostatic oscillations in single-walled carbon nanotubes

Using macroscopic quantum hydrodynamic formulation, we study the dispersion properties of electrostatic electron plasma oscillations in single-walled carbon nanotubes. The electrons and ions are considered uniformly distributed over the cylindrical surface of a nanotube thus forming a two-component (electron-ion) quantum plasma system. Electron degeneracy via Fermi-Dirac statistics as well as electron exchange and correlation effects is taken into account. It is found that the quantum (Bohm) potential arising due to fermionic nature of electrons and exchange-correlations effects has significant impact on the wave. The frequency of wave is influenced by variation in azimuthal index and radius of the nanotube. The results are analyzed numerically for typical systems for relatively longer wavelength waves and possible consequences are discussed. The results can be important in general understanding of the role of exchange-correlation potential in quantum hydrodynamic treatment of charge-carriers in nanotubes.

Waves in a bounded quantum plasma with electron exchange-correlation effects

Within a quantum hydrodynamic model, the collective excitations of the quantum plasma with electron exchange-correlation effects in a nano-cylindrical wave guide are studied both analytically and numerically. The influences of the electron exchange-correlation potential, the radius of the wave guide, and the quantum effect on the dispersion properties of the bounded quantum plasma are discussed. Significant frequency-shift induced by the electron exchange-correlation effect, the radius of the wave guide and the quantum correction are observed. It is found that the influence of the electron exchange-correlation, the radius of the wave guide and the quantum correction on the wave modes in a bounded nano-waveguide are strongly coupled.

Positron and electron energy levels in rare-gas solids.

The positron and electron band structures are calculated for the rare-gas solids Ne, Ar, Kr, and Xe on the basis of density-functional theory. The effects due to different approximations for the positron correlation and electron exchange-correlation potential are studied. The positron band structures obtained are compared with the measured band gaps in the 〈111〉 direction and with the measured positron work functions. A semiempirical positron correlation potential is presented.

Density-functional theory of hydrogen plasmas

The density-functional theory (DFT) for a system of ions and electrons having overall charge neutrality is presented. For a given temperature and free-electron density, the theory self-consistently determines the various pair-distribution functions, bound states, and the effective ion charge $\overline{Z}=Z\ensuremath{-}{n}_{b}$, where ${n}_{b}$ is the mean number of bound electrons per ion. With the use of a sufficiently large correlation sphere to represent the physically relevant part of the plasma, a Kohn-Sham-type Schr\odinger equation is solved for the electrons. The density-functional equations for the ions reduce to a Gibbs-Boltzmann equation containing an effective ion-correlation potential. The latter is obtained from the hypernetted-chain equation. The electron exchange-correlation potential is obtained from quantum many-body theory. The method is applied to an electron-proton plasma (EPP) for a number of physical situations. The machine-simulation (MS) results in the classical one-component-plasma limit, as well as the standard proton-in-jellium results, are correctly recovered in suitable limits. The MS results for the EPP plasma are limited by classical approximations, but are found to be in reasonable agreement with our DFT results which are probably more well founded. A shallow $1s$-like bound state appears with increase of temperature or decrease of density. The proton-pair distribution function in the EPP shows the onset of short-range order only when $\ensuremath{\Gamma}\ensuremath{\gtrsim}5$ or more. The electron-proton distribution function is found to be relatively insensitive to the details of the ion distribution for the static properties studied in this paper.

Optical properties of impurities in blende type II–VI semiconductors compounds

First-principles calculations have been used to study the structural, elastic, electronic, magnetic and thermal properties of zinc blende Zn1−xVxTe for x=0, 0.25, 0.50, 0.75 and 1 using the full-potential linearized augmented plane wave method (FP-LAPW) based on spin-polarized density functional theory (DFT). The electronic exchange-correlation potential is approached using the spin generalized gradient approximation (spin-GGA). The structural properties of the Zn1−xVxTe alloys (x=0, 0.25, 0.50, 0.75 and 1) are given for the lattice constants and the bulk moduli and their pressure derivatives. The elastic constants C11, C12 and C44 are calculated using numerical first-principles calculations implemented in the WIEN2k package. An analysis of the band structures and the densities of states reveals that Zn0.50V0.50Te and Zn0.75V0.25Te exhibit a half-metallic character, while Zn0.25V0.75Te is nearly half-metallic. The band structure calculations are used to estimate the spin-polarized splitting energies Δx(d) and Δx(pd) produced by the V(3d)-doped and s(p)–d exchange constants N0α (conduction band) and N0β (valence band). The p–d hybridization reduces the magnetic moment of V from its atomic charge value of 3µB and creates small local magnetic moments on the nonmagnetic Zn and Te sites. Finally, we present the thermal effect on the macroscopic properties of these alloys, such as the thermal expansion coefficient, heat capacity and Debye temperature, based on the quasi-harmonic Debye model.

Electron paramagnetic resonance of Mn 2+ in (NH 4) 2Co 2(SO 4) 3 and (NH 4) 2Ni 2(SO 4) 3 single crystals

First-principles calculations have been used to study the structural, elastic, electronic, magnetic and thermal properties of zinc blende Zn1−xVxTe for x=0, 0.25, 0.50, 0.75 and 1 using the full-potential linearized augmented plane wave method (FP-LAPW) based on spin-polarized density functional theory (DFT). The electronic exchange-correlation potential is approached using the spin generalized gradient approximation (spin-GGA). The structural properties of the Zn1−xVxTe alloys (x=0, 0.25, 0.50, 0.75 and 1) are given for the lattice constants and the bulk moduli and their pressure derivatives. The elastic constants C11, C12 and C44 are calculated using numerical first-principles calculations implemented in the WIEN2k package. An analysis of the band structures and the densities of states reveals that Zn0.50V0.50Te and Zn0.75V0.25Te exhibit a half-metallic character, while Zn0.25V0.75Te is nearly half-metallic. The band structure calculations are used to estimate the spin-polarized splitting energies Δx(d) and Δx(pd) produced by the V(3d)-doped and s(p)–d exchange constants N0α (conduction band) and N0β (valence band). The p–d hybridization reduces the magnetic moment of V from its atomic charge value of 3µB and creates small local magnetic moments on the nonmagnetic Zn and Te sites. Finally, we present the thermal effect on the macroscopic properties of these alloys, such as the thermal expansion coefficient, heat capacity and Debye temperature, based on the quasi-harmonic Debye model.