Local Density Approximation Approach Research Articles

Exploring Half-Metallicity in NiO via TM and NTM Doping: Insights from LDA and LDA-SIC approaches

This study utilizes first-principles calculations to investigate the magnetic properties of NiO doped and co-doped with transition metals (TM) such as vanadium (V), chromium (Cr), and manganese (Mn) at low concentrations. By employing local density approximation (LDA) and self-interaction corrected local density approximation (LDA-SIC), we uncover a pronounced half-metallic behavior in the modified NiO systems. Additionally, the introduction of nitrogen into the doped NiO results in a substantial shift in the density of states (DOS), transforming the material from a non-half-metallic to a distinctly half-metallic ferromagnetic state. These findings offer valuable insights into the potential of doped and co-doped NiO for advancing spintronic applications.

Optical and Electronic Structural Properties of Cu3N Thin Films: A First-Principles Study (LDA + U).

A comprehensive study on the electronic structure and optical properties of a Cu3N film is performed by the first-principles study using density functional theory. The Hubbard (U) term is added in the local density approximation approach for improvement of the theoretical band gap energy. The band structure of the Cu3N unit cell shows a strong hybridization of Cu 3d and N 2p orbitals in the near-valence band region (M) because of their antibonding states which are also observed by molecular orbitals (HOMO–LUMO). The conduction band is dominated by a very small amount of Cu 3p and N 2p orbitals. The density of states exhibits a negligible deformation in Cu–N bonding. The Cu3N thin film deposited by the DC magnetron-sputtering technique shows a polycrystalline structure with a nonstoichiometric Cu3N phase. The experimentally obtained optical band gap and refractive index of the Cu3N film are 1.44 eV and 2.14, respectively, which are comparable with those from the theoretical approximation.

Study of the elastic properties and wave velocities of rocksalt Mg1−xFexO: ab initio calculations

The composition dependence of the elastic constants, bulk modulus, shear modulus, Young's modulus, and compression and shear wave velocities along the different directions for the rocksalt Mg1−xFexO material system has been investigated. The calculations are based on the density functional theory using the full-potential augmented-plane-wave method. The exchange and correlation energies have been treated using three approaches, namely, the local density approximation (LDA), the generalized gradient approximation (GGA) of Perdew et al. and the GGA of Wu and Cohen (WC-GGA). It is found that all the approaches used show the same qualitative behavior for the features of interest versus alloy composition x. From the quantitative point of view, the GGA seemed to give better results than the LDA and WC-GGA approaches when compared to experiment. The trend appears to be consistent with those reported in previous calculations of the elastic constants for other semiconductor materials using the LDA and GGA methods.

FP-LAPW study of energy bands and optical properties of the filled skutterudite $$\hbox {CeRu}_{4}\hbox {As}_{12}$$ CeRu 4 As 12 with spin–orbit coupling

The density functional theory (DFT)-based fully relativistic version of the full-potential linearized augmented plane wave method with spin---orbit coupling (SOC) has been used to study the electronic and optical properties of the filled skutterudite $$\hbox {CeRu}_{4}\hbox {As}_{12}$$CeRu4As12. The exchange and correlation potential has been treated with the local density approximation (LDA). The analysis of the density of states and energy bands in the vicinity of the Fermi energy level suggests the semiconducting nature of the material with narrow indirect energy band gap of 0.11 eV; however, the gap value increases to 0.17 eV for without SOC calculation. Additionally, the modified Becke---Johnson (mBJ) potential has been utilized along with the LDA approach to estimate the precise value of the energy band gap of the material. The mBJ treatment enhances the energy band gap to ź0.2 eV. In order to understand the structural and mechanical properties of the sample material, the elastic constants are also estimated at ambient conditions. The analysis of the elastic constants suggests the brittle nature of the material whose stiffness is comparable with that of $$\hbox {CeOs}_{4}\hbox {Sb}_{12}$$CeOs4Sb12 and the covalent contribution is expected in the bonding. The optical response of the material has been studied from the energy bands, which reflects the metallic behavior of the material in the infrared region of frequency radiation and turns to act as opaque material with superluminal behavior at ultraviolet frequency radiation. The inclusion of the hybrid functional in the calculation suggests the metallic nature of the material.

Comparing models for the ground state energy of a trapped one-dimensional Fermi gas with a single impurity

We discuss the local density approximation approach to calculating the ground state energy of a one-dimensional Fermi gas containing a single impurity, and compare the results with exact numerical values that we have for up to 11 particles for general interaction strengths and up to 30 particles in the strongly interacting case. We also calculate the contact coefficient in the strongly interacting regime. The different theoretical predictions are compared to recent experimental results with few-atom systems. Firstly, we find that the local density approximation suffers from great ambiguity in the few-atom regime, yet it works surprisingly well for some models. Secondly, we find that the strong interaction theories quickly break down when the number of particles increase or the interaction strength decreases.

Structural and electronic properties of Er0.5Lu0.5B2 and LuB2 compounds by using the PBE0 hybrid functional

We report first-principles calculations to determine the structural and electronic properties of Er0.5Lu0.5B2 and LuB2 compounds, by using Density Functional Theory (DFT) and Full Potential Linearized Augmented Plane-Waves (FP-LAPW) method. For the description of the electron-electron interaction was used the Local Density Approximation (LDA), Generalized Gradient Approximation of Perdew-Burke-Ernzerhof (GGA-PBE) and PBE0 hybrid functional. From the density of states (DOS), it is found that the addition of a fraction of the exact Hartree- Fock exchange energy in PBE approximation, evidence the localization of the 4f-Er and 4f-Lu orbitals, which favours the polarization of the electronic spins of these orbitals in LuB2 and Er0.5Lu0.5B2 compounds. The PBE0 scheme is justified because it describes of more appropriate manner the electronic and magnetic properties of strongly correlated systems than the LDA and PBE approaches.

Magnetic exchange inα-iron fromab initiocalculations in the paramagnetic phase

Applying the local density approximation (LDA) and dynamical mean field theory (DMFT) to paramagnetic $\alpha $-iron, we revisit a problem of theoretical description of its magnetic properties. The analysis of local magnetic susceptibility shows that at sufficiently low temperatures $T<1500K$, both, $e_{g}$ and $t_{2g}$ states equally contribute to the formation of the effective magnetic moment with spin S=1. The self-energy of t_{2g} states shows sizable deviations from Fermi-liquid form, which accompanies earlier found non-quasiparticle form of e_{g} states. By considering the non-uniform magnetic susceptibility we find that the non-quasiparticle form of $e_{g}$ states is crucial for obtaining ferromagnetic instability in $\alpha $-iron. The main contribution to the exchange interaction, renormalized by the effects of electron interaction, comes from the hybridization between $t_{2g}$ and $e_{g}$ states. We furthermore suggest the effective spin-fermion model for $\alpha $-iron, which allows us to estimate the exchange interaction from paramagnetic phase, which is in agreement with previous calculations in the ordered state within the LDA approaches.

Structural, electronic, and optical properties of orthorhombic and triclinic BiNbO4 determined via DFT calculations

We performed ab initio calculations using the FPLAW method with the local density approximation (LDA) implemented in the WIEN2 k code for the orthorhombic (α) and triclinic (β) phases of BiNbO4. The modified Becke–Johnson exchange potential (mBJ)-LDA approach was also used to improve the electronic properties. The lattice constants calculated for both structures using the LDA are in good agreement with the experimental values. For the band structure calculations, the mBJ-LDA approach provides reasonable agreement for the band gap value compared with the LDA. The estimated (mBJ)-LDA band gap values are 2.89 eV (3.73 eV) and 2.62 eV (3.15 eV) for the α and β phases of BiNbO4, respectively. Significant optical anisotropy is clearly observed in the visible-light region. We also calculated and evaluated the electron energy loss spectrum for BiNbO4. This work provides the first quantitative theoretical prediction of optical properties and electron energy loss spectra for both the orthorhombic and triclinic phases of BiNbO4.

A first-principles study on the structural, elastic, electronic, and optical properties of CdRh2O4

The structural, elastic, electronic, and optical properties of CdRh2O4 with cubic \( (Fd\overline{ 3} m) \) and orthorhombic (Pnma) structures have been investigated using a pseudopotential plane wave (PP-PW) method within the local density approximation (LDA). The calculated lattice parameters agree reasonably with the experimental values. The single-crystal elastic stiffness constants Cijs of the cubic and orthorhombic phases are investigated using the stress–strain method. In addition, the polycrystalline elastic properties including bulk modulus, shear modulus, Young’s modulus, bulk modulus–shear modulus ratio, Poisson’s ratio, and elastic anisotropy ratio are determined based on Voigt–Reuss–Hill approach. The use of the hybrid functional sX-LDA leads to considerably improved electronic properties compared to standard LDA approach. On the other hand, the dielectric function, refraction index, reflectivity, conductivity function, and energy-loss spectra were obtained and analyzed on the basis of electronic band structures and density of states.

ChemInform Abstract: Structural, Elastic, Electronic and Optical Properties of Beryllium Chalcogenides BeX (X: S, Se, Te) with Zinc‐Blende Structure

Abstracttheoretical study

Structural, elastic, electronic and optical properties of beryllium chalcogenides BeX (X = S, Se, Te) with zinc-blende structure

The structural stability, elastic, electronic structures and optical properties of the BeX (X=S/Se/Te) cubic compounds in zinc-blende (B3) structure have been investigated using a pseudopotential plane wave (PP-PW) method within the generalized gradient approximation (GGA) and the local density approximation (LDA). The use of the hybrid functional sX-LDA leads to considerably improved electronic properties compared to standard GGA and LDA approaches. The calculated lattice parameters and bulk modulus agree reasonably with the previous results. The second-order elastic constants have been calculated and we also obtained phase transition pressure of BeX from B3 to NiAs (B8) structures. The enthalpy of formation, band structure, density of states and electric charge density is as well given. On the other hand, an accurate calculation of linear optical functions (the dielectric function, refraction index and reflectivity) is performed. The results obtained are compared with other calculations and experimental measurements.

The ground state binding energy of the closed shell nuclei with the density dependent Av18 effective interaction in LOCV method

This work presents the calculation of the ground state binding energy of some light closed shell nuclei such as 4He, 12C, 16O, 28Si, 32S, 40Ca and 56Ni. We use our channel-dependent effective two-body interactions data that are produced through the lowest order constrained variational (LOCV) method for asymmetric nuclear matter with the charge-dependent Av18 bare NN potential up to Jmax = 2 and Jmax = 5. The local density approximation approach in the harmonic oscillator basis and Brody-Moshinsky coefficients are used to produce the relative and center of mass dependent effective two-body potentials. We show that the ground state energies of the closed shell nuclei with Av18 (Jmax = 2) gives more binding with respect to Reid68 bare NN potential as well as Δ – Reid68. However, there is not much difference between the Av18 (Jmax = 5) and Reid68Day which has been defined up to Jmax=5. We conclude that the contributions of higher partial waves (J > 2) are not very important and two-body kinetic energy in J=1 channel is twice as that of J=0 which is not the case for the two-body potential energy. Finally, our work results are compared with other theoretical approaches and experimental data.

Origin of optical second-harmonic generation in spherical gold nanoparticles: Local surface and nonlocal bulk contributions

The second-harmonic generation of 150 nm spherical gold nanoparticles is investigated both experimentally and theoretically. We demonstrate that the interference effects between dipolar and octupolar plasmons can be used as a fingerprint to discriminate the local surface and non-local bulk contributions to the second-harmonic generation. By fitting the experimental data with the electric fields computed with finite-element method (FEM) simulations, the Rudnick and Stern parameters weighting the relative nonlinear sources efficiencies are evaluated and the validity of the hydrodynamic model and the local density approximation approaches are discussed.

Effect of Short Antiferromagnetic Correlations on the Normal and Superconducting Properties in Copper Oxides

The abnormal “normal” state and origin of high temperature superconductivity in cuprates are still not clear [1, 2]. The strong electron correlations (SEC) are known to be one of the main difficulties for the theory of high- cuprates. The conventional LDA (local density approximation) approach to the band structure fails in the regime of SEC. Various realistic multiband models of a layer at low energy result in the effective Hubbard or models [3 7]. The hybrid LDA+GTB scheme [8] generates the low-energy effective model with all parameters calculated ab initio.

Optical response of metallic and insulatingVO2 calculated with the LDA approach

We calculated the optical response of metallic and insulatingVO2 using the local density approximation (LDA) approach. The band structure calculation was basedon the full-potential linear-muffin-tin method. The imaginary part of the dielectric functionε2(ω) is related to the different optical transitions. The Drude tail in the calculation of themetallic phase corresponds to intraband d–d transitions. The calculation in theinsulating phase is characterized by the transitions to the band. The low-frequency features, 0.0–5.0 eV, correspond to V 3d–V 3d transitions, whereasthe high-frequency structures, 5.0–12 eV, are related to O 2p–V 3d transitions.The calculation helps to explain the imaginary part of the dielectric functionε2(ω), as well as the electron-energy-loss and reflectance spectra. The results reproduce not onlythe energy position and relative intensity of the features in the spectra, but also the mainchanges across the metal–insulator transition and the polarization dependence. The maindifference is a shift of about 0.6 eV in the calculation of the insulating phase. Thisdiscrepancy arises because the LDA calculation underestimates the value of the band gap.

Ab initio calculations for the absorption spectra and polarizabilities of small sulfur clusters

Absorption spectra for Sn clusters (n = 2...8) are calculated using an adiabatic time-dependent density functional formalism within the local density approximation (LDA). We compare the calculated spectra with those computed using a simple LDA approach. The time-dependent LDA (TDLDA) spectra display a significant blue shift with respect to the LDA spectra. The calculated spectra present a variety of features that can be used for comparison with future experimental investigations. We also obtain a significant threshold absorption, which can distinguish between different ground states of the sulfur clusters. In addition, the polarizabilities of the clusters are calculated by using the higher-order finite-difference pseudopotential density functional method in real space. We find that the polarizabilities of the clusters considered are higher than the value estimated from the `hard sphere' model using the bulk static dielectric constant. The computed polarizabilities per atom tend to decrease with increasing cluster size. The polarizabilities are closely related to the HOMO–LUMO gaps and the geometrical configurations.

Ground State Property of LiV2O4

The spinel structure LiV2O4 is studied by local densityapproximation (LDA) as well as including strong correlation correctionpotential, i.e. the LDA+U scheme, which concerns the stronglycorrelated interaction. With LDA, the orbitals of V 3d and O 2p arewell separated so that it presents purely metallic heavyfermion behaviour. The total energy of ferromagnetic phase is slightlylower than that of paramagnetic phase within the LDA approach. Thisimplies that the ferromagnetic instability as a consequence of spinfrustrated magnetism can be observed in experiments. The strongcorrelation interaction by using LDA+U enhances the exchange splitting.The heavy-fermion feature can be derived from the sharp peak around theFermi level from the density of states.

Ground state of heavy closed shell nuclei: An effective interaction and local density approximation approach

We study the ground-state properties of heavy closed-shell nuclei such as {sup 48}Ca, {sup 90}Zr, {sup 120}Sn, and {sup 208}Pb as well as {sup 4}He, {sup 16}O, and {sup 40}Ca. Similar to our recent work, the local density approximation in the harmonic oscillator basis and different channel-dependent effective two-body interactions that are generated through the lowest-order constrained variational calculation for asymmetric nuclear matter with the Reid68Day, Reid68, and {delta}-Reid68 potentials are used. Unlike nuclear matter, it is shown that Reid68 potential gives ground-state binding energies closer to the experimental data with respect to the {delta}-Reid68 potential and there is not much difference between Reid68 and Reid68Day potentials, which have been define up to J=5. The different channel-dependent effective interactions (J>2) and one- and two-body density distribution functions are discussed and they are compared with the results of other approaches such as the Brueckner local density approximation, correlated basis function, variational fermion hypernetted chain, variational cluster Monte Carlo, Brueckner-Hartree-Fock, fermionic molecular dynamics, and coupled cluster. Finally it is concluded that the three-body force (isobar degrees of freedom) is very important for light (heavy) nuclei because in the most of recent many-body calculations, it is observed that the available two-body nuclear forcesmore » usually underbind light nuclei and overbind heavy nuclei and nuclear matter.« less

Density functional theory investigation of CN on Cu(1 1 1), Ni(1 1 1) and Ni(1 0 0)

The adsorption of CN on Cu(1 1 1), Ni(1 1 1) and Ni(1 0 0) has been investigated using density functional theory (DFT). While experimental studies of CN on Cu(1 1 1) show the molecular axis to be essentially parallel to the surface, the normally-preferred DFT approach using the generalised gradient approximation (GGA) yields a lowest energy configuration with the C–N axis perpendicular to the surface, although calculations using the local density approximation (LDA) do indicate that the experimental geometry is energetically favoured. The same conclusions are found for CN on Ni(1 1 1); on both surfaces bonding through the N atom is always unfavourable, in contrast to some earlier published results of ab initio calculations for Ni(1 1 1)/CN and Ni(1 0 0)/CN. The different predictions of the GGA and LDA approaches may lie in subtly different relative energies of the CN 5σ and 1π orbitals, a situation somewhat similar to that for CO adsorbed on Pt(1 1 1) which has proved challenging for DFT calculations. On Ni(1 0 0) GGA calculations favour a lying-down species in a hollow site in a geometry rather similar to that found experimentally and in GGA calculations for CN on Ni(1 1 0).

Electronic structures of V-doped anatase TiO 2

First-principles calculations using the full-potential linearized augmented plane-wave method have been performed to investigate the electronic structure of V-doped TiO 2 in the anatase modification. In calculations with local density approximation (LDA), V 3d states are located at the bottom of the conduction band of the TiO 2 host. The V-doped TiO 2 was shown to be a half-metal. However, in calculations with LDA+ U (Hubbard coefficient) approach that incorporates strongly correlated interactions of both Ti and V 3d electrons, the band gap of TiO 2 host was obtained as 3.18 eV, very close to the experimental result of 3.2 eV. Additionally, spin-polarized V 3d states were obtained which are gap states located in the band gap of TiO 2 host. The V-doped TiO 2 was indicated to be an insulator. An analysis of the V 3d orbital splitting in a D 2d local symmetry of the TiO 2 host indicates that the LDA+ U approach presents a more accurate description on the electronic structure of V-doped TiO 2 than the standard LDA approach. In addition, the energy of V-doped TiO 2 in the ferromagnetic phase was calculated with LDA+ U to be 0.034 eV lower than that in the anti-ferromagnetic phase. This energy difference corresponds to 400 K, close to the Curie temperature, ∼405 K in V-doped TiO 2.