Local Density Approximation Potential Research Articles

Exchange-correlation potential built on the derivative discontinuity of electron density.

Electronic structures are fully determined by the exchange-correlation (XC) potential. In this work, we develop a new method to construct reliable XC potentials by properly mixing the exact exchange and the local density approximation potentials in real space. The spatially dependent mixing parameter is derived based on the derivative discontinuity of electron density and is first-principle. We derived the equations for solving the mixing parameter and proposed an approximation to simplify these equations. Based on this approximation, this new method gives reasonable predictions for the ionization energies, fundamental gaps, and singlet-triplet energy differences for various molecular systems. The impact of the approximation on the constructed XC potentials is examined, and it is found that the quality of the XC potentials can be further improved by removing the approximation. This work demonstrates that the derivative discontinuity of electron density is a promising constraint for constructing high-quality XC potentials.

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.

Spectral permittivity tensor and density functional theory calculations on the Heusler compound Co2FeAl0.5Si0.5

The Heusler compound ${\mathrm{Co}}_{2}{\mathrm{FeAl}}_{0.5}{\mathrm{Si}}_{0.5}$ is an interesting material for spintronic applications due to its predicted half-metal ferromagnetic character with a large band gap in the minority states. In this work, we present the optical and magneto-optical properties of a ${\mathrm{Co}}_{2}{\mathrm{FeAl}}_{0.5}{\mathrm{Si}}_{0.5}$ bulk sample at room temperature. The spectral permittivity is found to be dominated by an absorption peak at 1.4 eV, originating mostly from absorptions by minority electrons. The best agreement between the experimentally obtained spectral permittivity tensor and the ab initio calculated one is for the local density approximation potential, closely followed by the generalized gradient approximation potential. However, the half-metallic ferromagnet character with $100%$ spin polarization is preserved only in calculations employing the Coulomb interaction correction (+U). This suggests that ${\mathrm{Co}}_{2}{\mathrm{FeAl}}_{0.5}{\mathrm{Si}}_{0.5}$ is probably not a half metal as a single minority $d$-band dips below the Fermi level.

Calculated electronic, transport, and related properties of zinc blende boron arsenide (zb-BAs)

We present the results from ab-initio, self-consistent density functional theory (DFT) calculations of electronic, transport, and bulk properties of zinc blende boron arsenide. We utilized the local density approximation potential of Ceperley and Alder, as parameterized by Vosko and his group, the linear combination of Gaussian orbitals formalism, and the Bagayoko, Zhao, and Williams (BZW) method, as enhanced by Ekuma and Franklin (BZW-EF), in carrying out our completely self-consistent calculations. With this method, the results of our calculations have the full, physical content of density functional theory (DFT). Our results include electronic energy bands, densities of states, effective masses, and the bulk modulus. Our calculated, indirect band gap of 1.48 eV, from Γ to a conduction band minimum close to X, for the room temperature lattice constant of 4.777 Å, is in an excellent agreement with the experimental value of 1.46 ± 0.02 eV. We thoroughly explain the reasons for the excellent agreement between our findings and corresponding, experimental ones. This work provides a confirmation of the capability of DFT to describe accurately properties of materials, if the computations adhere strictly to the conditions of validity of DFT, as done by the BZW-EF method.

Vibrational and dielectric properties of AlN: A first-principles study

The vibrational and dielectric properties of zinc-blende aluminum nitride (B3-AlN) were investigated within the framework of density functional perturbation theory. The phonon frequencies at the Brillouin zone center, the static dielectric constant, and the electronic dielectric constant were reported. The results of our studies were analyzed and discussed with respect to the available experimental and theoretical data. We found that the generalized gradient approximation potential resulted in more accurate phonon frequencies than those obtained using the local density approximation potential. The contributions to the static dielectric tensor due to purely electronic screening and infrared-active phonon modes were analyzed. The phonon, dielectric, refractive index, extinction coefficient and infrared reflectance spectra of B3-AlN were reported, and their values suggest that B3-AlN has good transmission properties in the spectral range above 1000cm−1 and below 400cm−1.

Ab-initio calculations of electronic, transport, and structural properties of boron phosphide

We present results from ab-initio, self-consistent density functional theory calculations of electronic and related properties of zinc blende boron phosphide (zb-BP). We employed a local density approximation potential and implemented the linear combination of atomic orbitals formalism. This technique follows the Bagayoko, Zhao, and Williams method, as enhanced by the work of Ekuma and Franklin. The results include electronic energy bands, densities of states, and effective masses. The calculated band gap of 2.02 eV, for the room temperature lattice constant of a = 4.5383 Å, is in excellent agreement with the experimental value of 2.02 ± 0.05 eV. Our result for the bulk modulus, 155.7 GPa, agrees with experiment (152–155 GPa). Our predictions for the equilibrium lattice constant and the corresponding band gap, for very low temperatures, are 4.5269 Å and 2.01 eV, respectively.

Vibrational and dielectric properties of magnesium aluminate spinel: A first-principles study

The vibrational and dielectric properties of MgAl 2O 4 are investigated within the framework of density functional perturbation theory. Results of phonon frequencies at the Brillouin zone center, static dielectric constant, and electronic dielectric constant are reported. In comparison with experimental results, we find that the generalized gradient approximation potential results in more accurate phonon frequencies than local density approximation potential does. Dielectric, refractive index, extinction coefficient and infrared reflectance spectra of MgAl 2O 4 are given, and the figures suggest that MgAl 2O 4 presents good transmission properties in the spectrum range above 1000 cm − 1 and below 300 cm − 1 .

Predictions of electronic, structural, and elastic properties of cubic InN

We present theoretical predictions of electronic, structural, and elastic properties of cubic indium nitride in the zine-blende structure (c-InN). Our ab initio, self-consistent calculations employed a local density approximation potential and the Bagayoko, Zhao, and Williams implementation of the linear combination of atomic orbitals. The theoretical equilibrium lattice constant is 5.017Å, the band gap is 0.65eV, and the bulk modulus is 145GPa. The band gap is 0.74eV at an experimental lattice constant of 4.98Å.

Electronic structure ofCeCoIn5

A fully self-consistent procedure for obtaining the electronic structure of the superconductor ${\mathrm{CeCoIn}}_{5}$ is carried out by means of a local-density approximation potential within the augmented plane-wave framework. The results show that the electronic dynamic is fundamentally governed by the $4f$ states of Ce and $3d$ of Co which are close to ${E}_{F}.$ In addition, the weak hybridization between the states in the CeIn layer and the subsystem ${\mathrm{CoIn}}_{4}$ may imply a two dimensional structure which can serve as a scenario for a square Kondo/Ruderman-Kittel-Kasuya-Yosida lattice.

First Principles Molecular Dynamics of Dense Plasmas

Ab initio molecular dynamics calculations are performed for the equation of state of aluminum, spanning condensed matter and dense plasma regimes. Electronic exchange and correlation are included with either a zero- or finite-temperature local density approximation potential. Standard methods are extended to above the Fermi temperature by using final state pseudopotentials to describe thermally excited ion cores. The predicted Hugoniot equation of state agrees well with earlier plasma theories and with experiment for temperatures from 0 to 3 x 10(6) K.

Evaluation of isomorphous models of alloys

Order-$N$ methods for calculating the electronic structure of clusters containing hundreds of atoms using realistic self-consistent density-functional theory local-density approximation potentials make it possible to test alloy theories more definitively. Tests are carried out on isomorphous models of alloys in which the atoms of each species are treated as identical. In contrast, the order-$N$ calculations lead to a polymorphous model in which all of the atoms are unique. Isomorphous models are seen to reproduce average densities of states and cohesive energies surprisingly well, in spite of their deficiencies in other areas.

The elastic scattering on jellium clusters

The following calculations are based on the local density approximation potential (LDA) of W. Ekardt for the spherical jellium-background model (SJBM). Taking into account the smooth shape of the potential, the WKB approximation was used to calculate the energy and angular dependence of the electron scattering cross-sections fo rsmall Na clusters. The number of phase shifts needed to describe the scattering in the range of energies <4.5 eV increases with the size of cluster. The calculated elastic electron scattering cross-sections for the Na clusters, corresponding to the shell closings (8, 20, 40), are exhibiting a pronounced peak structure, correlated with resonance states. The computed peaks of the angular dependences of the cross-sections on energy are shifted to small angles with increasing the cluster size. The absence of fragmentation at these small electron energies presents a challenge for the experimentalists.

Mono- and dilayer analogues of crystalline atomic hydrogen

As well as being of interest in their own right, many of the essential features of the lattice properties of crystalline atomic hydrogen should be interpretable in terms of the lattice properties of one- or two-layer hydrogen films. Here we present optimized equilibrium lattice parameters for monatomic hydrogen one- and two-layer films in several Bravais lattices as determined by all electron, full potential localdensity-approximation calculations.