Exchange-correlation Effects Research Articles

Computational investigation of the structural, mechanical and acoustic characteristics of rare earth based Heusler compounds

The study undertaken on new Heusler compounds to uncover their crystal stability, structural parameters, elastic constants and moduli along with other important related properties. The scheme consisted of PBE-sol potential to treat exchange correlation effects. All the compounds consist of cubic structure where the elastic constants range from 6.57 Å for LuPd2Cd and 6.87 Å for GdAu2Cd. Compounds show high bulk modulus above 80 GPa. The elastic constants calculated were in excellent matching with the any available data while some of the data presented in the study is reported for the first time. Ductile and brittle nature was explored thoroughly for all compounds. Melting temperature, velocity (longitudinal, transverse) of sound, hardness along with other important elastic characteristics were also calculated using different available and established equations. Current work can be very useful to bring forth new results which may help further exploration of these less explored materials.

First-principles Study on Structural and Electronic Properties: The Li Based of Full-Hesulter Alloys LiGa2Ir

Abstract: Due to their excellent electronic properties, full-Heusler compounds have become one of the most interesting families of alloys in superconductivity. More recently, computational methods have been actively employed to support the rapid discovery of new complete Heusler alloys by identifying stable compositions with desired properties. Therefore, we investigated the stability, structure, and electronic properties of the lithium-based Heusler compound LiGa2Ir using first-principles calculations. We explored the effects of exchange-correlation, namely Perdew-Burke-Ernzerhof (PBE), PBE+U, and Tran-Blaha modified Becke-Johnson potentials, as well as the effect of heavy metal spin-orbit coupling on these Heusler compounds. The results show that LiGa2Ir is energetically stable, and the obtained lattice parameter value (a = 6.0927 Å) agrees with the experimental results. LiGa2Ir exhibits metallic behavior under all three exchange-correlation estimates. A much stronger spin-orbit coupling effect is observed for electronic states with energies below the Fermi level EF, especially in the Tran-Blaha modified Becke-Johnson approximation. Significant spin-orbit coupling effects are evident from the total and partial density of states figures, especially in the energy range from -4.5 eV to -2 eV. The contributions from Ir-d and Ga-p orbitals are the largest, while the contribution from the Li atom is small. Our findings will benefit future theoretical and practical work on lithium-based full-Heusler alloys. Keywords: Full-Heusler, DFT, Spin-orbit coupling, Electronic properties, Density of states.

High-throughput screening on optoelectronic properties of two-dimensional InN/GaN heterostructure from first principles.

A novel 2D InN/GaNlateral heterostructure (LHT) was simulated by stitching monolayer of 2D InN and monolayer of 2D GaN. The structural stability, electronic structure, and optical properties were systematically investigated using first-principle calculations and by considering the effects of strain. The results indicated that the designed heterostructure has a direct bandgap of 2.26eV which is further affected by applied biaxial strain. The bandgap of 2D InN/GaN lateral heterostructure decreases with the increase in biaxial strain, and tensile strain triggers a direct-to-indirect energy gap changeover at + 6%. Additionally, under compressive strain, heterostructure remains a direct bandgap semiconductor. Furthermore, the strain significantly affects the optical characteristics of lateral heterostructure. It has been noticed that the first optical absorption peak moves from 2.51eV (ɛ = - 4%) to 1.40eV (ɛ = 10%). Therefore, 2D InN/GaN lateral heterostructure provides an approachable way for utilizing in optoelectronic devices through the creation of in-plane lateral heterostructures. We performed all the computations using a self-consistent method based upon density functional theory. We used the PBEsol functional in the GGA to account for the exchange-correlation effects. We introduced a 10-Å vacuum region in the z-direction to avoid interaction between periodic images. We considered non-negligible weak dispersion correction in the lateral heterostructure using Grimme's DFT-D3 approach. In this study, we also computed the electrical and optical properties employing the local modified Becke-Johnson (lmBJ) exchange potential under meta-GGA functional to obtain more precise results.

FP-LMTO simulation of the physical properties of arsenic-based binary XAs(X = Sc, and Al) compounds

This paper presents a simulation of the structural and optoelectronic properties of Scandium Arsenide (ScAs) and Aluminum Arsenide (AlAs) compounds. Theoretical modeling was performed using ab initio first-principles calculations, specifically the density functional theory (DFT), and the Mindlab numerical software. The software used two methods: the full-potential muffin-tin orbital method (FP-LMTO) and the full-potential plane-wave method (FP-LAPW). These two methods are employed to solve the Schrödinger equation. The exchange correlation effects have been computed using two different approximations: the generalized gradient approximation (GGA) and the local density approximation (LDA). Our findings indicate that the zinc blende structure (B3) is the stable phase, while the Wurtzite phase (B4) is metastable for the AlAs compound. On the other hand, the ScAs compound crystallizes in the NaCl phase (B1). The AlAs compounds undergo three phase transitions: [Formula: see text], [Formula: see text] and [Formula: see text]. In contrast, ScAs does not undergo any transition. The obtained results for equilibrium energies, lattice parameters and gap energies are in closer agreement with the experimental and theoretical data. The AlAs compound exhibits a semiconducting character, while ScAs exhibits a semi-metallic character. Additionally, the refractive index of these two compounds is similar to that of silicon, which is crucial for their application in photovoltaic cells.

An ab initio analysis of the electronic, optical, and thermoelectric characteristics of the Zintl phase CsGaSb2

We present and analyze the findings of a comprehensive ab initio computation that examines the electronic, optical, and thermoelectric characteristics of a recently synthesized Zintl compound known as CsGaSb2. The electronic and optical characteristics were examined using the DFT-based FP-L/APW+loapproach. Toaddress the exchange–correlation effects, we employed the GGA-PBEsol and TB-mBJ approaches.The CsGaSb2 semiconductor exhibits an indirect bandgap of 0.695 eV when analyzed with the GGA-PBEsol approach, and a bandgap of 1.254 eV when analyzed with the TB-mBJ approach.The PDOS diagrams were used to discover the origins of the electronic states that make up the energy bands. The charge density study reveals that the Ga-Sb link within the [GaSb2] block is mostly governed by a covalent character, whereas the cation Cs+ and polyanion [MSb2]−bonding is predominantly ionic. The frequency dependence of macroscopic linear optical coefficients was evaluated over a broad range of photon energies from 0 to 25 eV. The thermoelectric characteristics were investigated via the Boltzmann kinetic transport theoryassuming a constant relaxation time.The compound’s figure of merit at a temperature of 900 K is roughly 0.8.

Dynamic exchange correlation effects in the strongly coupled electron liquid

The first quasiexact path integral Monte Carlo (PIMC) investigation of the dynamic local field correction G̃(q,zl;rs,Θ) in the imaginary Matsubara frequency domain is reported, focusing on the unpolarized uniform electron gas in the warm dense matter and strongly coupled regimes. The impact of dynamic exchange–correlation effects on the static structure factor is investigated. A straightforward explanation is provided for previously reported spurious effects in the so-called [Dornheim , ], where the frequency dependence of the local field correction is neglected. The comprehensive analysis of the asymptotic Matsubara order behavior, the density dependence, and the temperature dependence hints at the intriguing possibility of constructing an analytical four-parameter representation of G̃(q,zl;rs,Θ) valid for a substantial part of the uniform electron gas phase diagram, which would constitute key input for thermal density functional theory simulations. Published by the American Physical Society 2024

Pressure effect investigation of structural, electronic, elastic and magnetic properties of X2CrSb (X = Mn, Co and Cu) Heusler alloys

Using the plane-wave pseudo-potential approach and generalized-gradient approximation for the exchange–correlation effects in the framework of the density functional theory, the structural, electronic, elastic and magnetic properties of X2CrSb ( ▪ and Cu) Heusler alloys were investigated. For ▪ , a structural phase-transition from XA to L21-phase is expected at 8.933GPa. This compound exhibits half-metallic behavior before becoming a magnetic metal at 17.5GPa. The ▪ is a half-metal under expansion and nearly half-metal above 1GPa. The total magnetic moments for ▪ , ▪ and ▪ are respectively equal to 5.0μB, 1.0μB and 3.4μB, and are mainly localized on Cr except for ▪ in XA-phase where the magnetic moment is localized on Mn. The DOS analysis shows weak spin-polarizations for ▪ and a higher polarization under expansion for ▪ and ▪ . Under compression, the polarization is weakened in ▪ , it remains at a high level before it vanishes at 29.4μB in ▪ .

Ab initio density response and local field factor of warm dense hydrogen

We present quasi-exact ab initio path integral Monte Carlo (PIMC) results for the partial static density responses and local field factors of hydrogen in the warm dense matter regime, from solid density conditions to the strongly compressed case. The full dynamic treatment of electrons and protons on the same footing allows us to rigorously quantify both electronic and ionic exchange–correlation effects in the system, and to compare the results with those of earlier incomplete models such as the archetypal uniform electron gas or electrons in a fixed ion snapshot potential that do not take into account the interplay between the two constituents. The full electronic density response is highly sensitive to electronic localization around the ions, and our results constitute unambiguous predictions for upcoming X-ray Thomson scattering experiments with hydrogen jets and fusion plasmas. All PIMC results are made freely available and can be used directly for a gamut of applications, including inertial confinement fusion calculations and the modeling of dense astrophysical objects. Moreover, they constitute invaluable benchmark data for approximate but computationally less demanding approaches such as density functional theory or PIMC within the fixed-node approximation.

Electron acoustic solitary waves in relativistically quantum magnetoplasmas with electron exchange correlation effects

The propagating of electron acoustic solitary waves (EASWs) in relativistically magnetized quantum plasmas which consists inertial cold electrons, inertialess hot electrons and stationary background ions have been theoretically investigated. The modified Zakharov-Kuznetsov (ZK) equation is derived by adopting the standard reductive perturbation method to describe the nonlinear evolution of the EASWs. After discussing the effects of various parameter values on the solitary structures, it is shown that the solitary structures are very sensitive to the relativistic degeneracy effect, the cold to hot electrons number density ratio and the electron exchange correlation effects. The numerical analysis can be well described by the existing analytical theory. Our results may be useful in explaining the physics behind the formation of the EASWs in both astrophysical and laboratory plasmas.

Exchange-correlation effects in interatomic energies for pure density functionals and their application to the molecular energy prediction.

In this proof-of-concept paper, we show how exchange-correlation effects can be simply recovered for interatomic energies within the interacting quantum atoms decomposition when local, gradient generalized, or meta-gradient generalized approximations are used in density functional theory (DFT) calculations. We also demonstrate how inhomogeneity and non-local effects can be introduced even from a pure local scheme, without resorting to any orbital information. Finally, we provide numerical evidence on a database of selected energetic molecules that this decomposition scheme can be efficiently used to build accurate models for the prediction of molecular energies from an initial "cheap" DFT calculation.

Meta-GGA study of 2D AlN/BN planer heterostructure and performance enhancement via strain engineering.

The 2D AlN/BN planer heterostructure is a promising wide band gap semiconductor, but systematic studies of its bandgap and optical characteristics under applied strain are scarce. Here, the engineering property of 2D AlN/BN comprising bandgap nature transition and optical absorption capability (from unstrained to strained) have been investigated using density functional theory calculations. The formation energy calculations confirm the stability of the simulated nanoheterostructure. The electronic band structure calculations demonstrate that nanoheterostructure is an indirect bandgap material with a large bandgap of 5.26 eV, which can be modified effectively by applying strain. According to the calculations, the transition from indirect to direct band gap behavior has been observed at +15% biaxial strain with 2.71 eV band gap energy. Meanwhile, calculations for optical absorption and dielectric function reveal that the system has significant absorption peaks in the ultraviolet region which are very sensitive to applied strain. As strain increases, the first absorption peaks are shifted towards a lower energy range from 5.73 eV (Ꜫ= 0 %) to 3.76 eV (Ꜫ = +15%), which features an enhancement of optical absorption for solar and solar-blind regions. Furthermore, we determined that the band edge positions in 2D AlN/BN straddled the water redox potential under strain, indicating its effectiveness as a proficient photocatalyst. These characteristics make 2D AlN/BN planer nanoheterostructure a promising candidate for applications in optoelectronics and photocatalytic water splitting performance. First principles computations based on density functional theory were employed to carry out all the calculations with a self-consistent approach. For solving the Kohn-Sham equations, the first principles dependent full-potential linearized augmented plane wave scheme were adopted. For addressing the exchange-correlation effects, the generalized gradient approximation of PBEsol functional was used. To prevent interaction between the periodic images, we have inserted a vacuum region of 10 Å in the z-direction. Non-negligible weak dispersion corrections in nanoheterostructure were considered by using the DFT-D3 method of Grimme's. The locally modified Becke-Johnson (lmBJ) exchange potential has also been applied to compute electronic and optical properties in this research to obtain more accurate information.

Ab-initio study of strain-tunable g-GaN/BN nanoheterostructure for optoelectronic and photocatalytic applications.

Two-dimensional (2D) nanoheterostructures of materials, integrating various phase or materials into a single nanosheet have stimulated large-scale research interest for designing novel two dimensional devices. In contemporary analysis present work, we examined the structural and electronic properties of the isolated 2D BN and GaN monolayers. We have investigated the structural stability and optoelectronic and photocatalytic response of the g-GaN/BN nanoheterostructure along with its response to strain. Nanoheterostructure g-GaN/BN is predicted to be a direct bandgap semiconductor with wide gap of 4.45eV, whose value can be effectively modulated by applied strain ( , ranging from 4.55 ( = - 4%) to 3.58eV ( = 8%). We also discovered that the tensile strain of 8% can substantially tune the direct bandgap of nanoheterostructure to indirect band gap nature. Even more important, the biaxial tensile strain engineering accentuates an enhancement of optical absorption in the UV region, broadening the light harvesting of the g-GaN/BN nanoheterostructure with the shifting of first absorption peak from 4.64 ( = - 4%) to 3.71eV ( = 8%). Furthermore, strain-tuned band edge potentials arrangement perfectly fits the water reduction and oxidation redox potentials. Our findings portend that the g-GaN/BN nanoheterostructure has application in prospective nanoscale optoelectronic devices and photocatalytic hydrogen evolution system. First principles calculations in this study are performed using density functional theory. Generalized gradient approximation within PBEsol functional employed to address the electron-electron exchange-correlation effects. For avoiding periodic interactions between the layers, we have inserted a vacuum region of thickness 10Å in the z-direction. For ensuring the convergence accuracy of the computed results, convergence criteria of the iteration process is set to be 0.0001eV. Local modified Becke-Johnson, a semi local functional, is applied for calculating electronic and optical properties for more accuracy of results. As in layered 2D nanoheterostructure, a factual depiction of the van der Waals interactions cannot be provided by conventional DFT techniques. Accordingly, in order to incorporate these interactions, we had employed the dispersion correction method of Grimme's.

Unveiling the mechanical, structural, thermoelectric, and optoelectronic potential of K2NaGaBr6 and K2RbTlBr6 double perovskites for sustainable technologies

Double perovskite halide's remarkable physical qualities and ease of synthesis have drawn much interest in the past few years. To analyze the structural and thermodynamic stability, elastic traits, optical, and thermoelectric analysis of the double perovskites K2NaGaBr6 and K2RbTlBr6, FP-LAPW technique is employed in current work. Exchange correlation effects are treated with PBE-GGA and TB-mBJ approximations. Thermodynamic stability of structures is ensured with computed phonon curves and negative formation energies. Goldsmith tolerance factor and octahedral tilting justify the cubic phase of both perovskites. Mechanical attributes justify Born’s stability criteria and double perovskites' anisotropic and ductile nature. The semiconducting nature is confirmed by electronic band structures with direct bandgap of 1.43 eV and 3 eV for K2NaGaBr6 and 1.48 eV and 2.51 eV for K2TlRbBr6 with PBE-GGA and TB-mBJ, respectively. Optical properties for K2NaGaBr6 and K2RbTlBr6 reveal significant absorption of electromagnetic waves in visible and UV regions. Furthermore, thermoelectric response for both double perovskites is computed using BoltzTraP code, which reveals their significant abilities for usage in thermoelectricity and renewable energy applications.

Bound state energies and critical bound region in the semiclassical dense hydrogen plasmas

We calculate the bound state energies of the hydrogen atom in semiclassical dense hydrogen plasmas modeled by the effective screened interaction potential developed by Ramazanov et al. [Phys. Rev. E 92, 023104 (2015)]. It is shown that the quantum degenerate and exchange-correlation effects of plasma electrons do not play significant roles in the region where the system exhibits bound states. The bound-continuum critical transition lines and the distribution of the ground state energies in the plasma density-temperature phase diagrams are obtained, both with and without taking into account the screening effect of the plasma ions. The dipole transition oscillator strengths and static dipole polarizabilities of the electron-ion subsystems in semiclassical dense hydrogen plasmas are calculated in a wide range of plasma parameters.

First-Principles Analysis on the Optoelectronic, Structural, Elastic and Transport Characteristics of Novel Fluoroperovskites Cs2TlAgF6 for Green Technology

Cs-based perovskites hold immense significance in the field of green technology due to their unique properties, offering promising avenues for efficient, low-cost devices. In this theoretical work, DFT has been employed to extensively scrutinize the physical properties of double fluoroperovskites Cs2TlAgF6. The modified Becke Johnson functional was used to take exchange-correlation effects into consideration accurately. From the calculated value of formation energy, volume optimization curve, Goldsmith tolerance factor and octahedral tilting, the structural stability is demonstrated. The band structure of Cs2TlAgF6 depicts a direct bandgap of 2.21 eV, proving its semiconducting nature. This study also assessed the mechanical properties in detail, showing the ductile character of Cs2TlAgF6. A thorough examination of optical characteristics reveals the potential application in a variety of photovoltaic devices due to its strong absorption in visible region. The transport attributes are accessed through large ZT value and other thermal parameters. With its exceptional heat-to-electricity conversion properties, this material shows promise for applications in thermoelectric devices, offering a sustainable way to generate electricity from waste heat. The larger value 0.788 of ZT depicts that material exhibit sufficient potential for generating energy from waste heat.

Sodium-based di-chalcogenide: a promising material for tandem solar cells

Compounds based on chalcogen elements are widely studied currently due to their many interesting applications for electronic devices. The sodium-based dichalcogenide (NaNbS2) is a fascinating material with storage and conversion energy applications. In this paper, we conduct a first-principles investigation of the structural and thermodynamic stability and electronic properties of this material. We analyze a total of four structures to find the ground state using a fourth-order Birch–Murnaghan equation of state: the α and η related to the A-phase and the ζ 1 and ζ 2 related to the B-phase. We carefully address the exchange-correlation effects using the semi- local GGA-PBEsol targeted for solids. To analyze the electronic structure with higher accuracy, we implement the quasi-particle G o W o approximation. Our results for the fourth-order Birch–Murnaghan equation show that the most thermodynamically stable phase at zero temperature is α. To provide experimentalists insights about the possible routes to grow these materials, we calculated the convex hull of the α-model and ζ 1-model, finding that both are energetically stable. Finally, the calculated band gap with quasiparticle corrections for the α-model is 1.03 eV, which suggests possible applications of this material as a bottom cell in modern solar cells.

Topological semimetals in the ZrB5 (B = Se, Te) material class: Weyl points and electronic properties

In the present work, the electronic structure, elastic parameters, density of states (partial and total), optical properties, and charge density of ZrB5 (B = Se, Te) have been investigated by means of first principles calculations. The generalized gradient approximation has been used for modeling the exchange-correlation effects. It has been observed that the calculated lattice parameter values are in agreement with the values in the literature. The second-order elastic constants were calculated, and the other related quantities have also been estimated. The electronic band structures and the partial density of states corresponding to these band structures of ZrSe5 and ZrTe5 are examined, and it is understood that ZrTe5 and ZrSe5 are narrow band semiconductors or semimetals. Finally, the electron energy loss function (ELS) spectra and charge density of ZrB5 are calculated and interpreted.

Bound-State Breaking and the Importance of Thermal Exchange-Correlation Effects in Warm Dense Hydrogen.

Hydrogen at extreme temperatures and pressures is of key relevance for cutting-edge technological applications, with inertial confinement fusion research being a prime example. In addition, it is ubiquitous throughout our universe and naturally occurs in a variety of astrophysical objects. In the present work, we present exact ab initio path integral Monte Carlo (PIMC) results for the electronic density of warm dense hydrogen along a line of constant degeneracy across a broad range of densities. Using the well-known concept of reduced density gradients, we develop a new framework to identify the breaking of bound states due to pressure ionization in bulk hydrogen. Moreover, we use our PIMC results as a reference to rigorously assess the accuracy of a variety of exchange-correlation (XC) functionals in density functional theory calculations for different density regions. Here, a key finding is the importance of thermal XC effects for the accurate description of density gradients in high-energy-density systems. Our exact PIMC test set is freely available online and can be used to guide the development of new methodologies for the simulation of warm dense matter and beyond.

Exchange-correlation effects on the structural, electronic, and optical properties of Sr2RuO4 using DFT calculations

We perform a first principle study on the electronic, structural, and optical properties of Sr2RuO4 by various functionals: LSDA, GGA, GGA-mBJ, PBE-D3, optB88-vdW, vdW-DF2 and HSE06 using the plane-wave method of density functional theory (DFT) in the presence of the spin-orbit coupling (SOC) and Coulomb interaction parameter, U. The dynamical stability and the thermal stability are calculated via phonon dispersions and ab initio molecular dynamics simulations, respectively. The band structure calculation and the orbital-resolved density of states of LSDA and the schemes of GGA reveal different ground state. For GGA-mBJ and the hybrid functional, there is an indirect gap in the band structure. In the case of vdW functionals, our findings are in agreement with GGA. We compute a variety of optical responses and compare them with existing experimental studies. The results of the dielectric function suggest that GGA-mBJ (LSDA and GGA) may better account for the experimental findings in the presence (absence) of SOC at the infrared spectral region (infrared and visible spectral regions). We observe that the optical responses are strongly influenced by SOC and intraband transitions. Among the optical spectra, we focus more on the electron energy loss spectrum, which depends on the excitations, the exchange-correlation effects, and the multiorbital nature of Sr2RuO4.

Theoretical and experimental study of the optoelectronic, thermodynamic and vibrational properties of the nanostructure of m-WO3

Tungsten trioxide (WO3), an n-type semiconductor, has attracted attention due to its diversity of properties, such as catalytic activity, gas sensing capabilities, photochromic behavior, and its ability to absorb both ultraviolet and visible light. This study aimed to investigate the monoclinic phase of the synthesized WO3 (m-WO3) through a combination of computational and experimental studies. We present the results of a theoretical investigation on m-WO3 using first-principles calculations (ab initio) and the pseudopotential model of plane waves. The Density Functional Theory (DFT) was employed, utilizing both the Local Density Approximation (LDA) and Generalized Gradient Approximation (GGA) to account for exchange potential and correlation effects. Structural properties, electron band structure, electron density of states, and optical properties (reflectivity and optical absorption) were computed for the optimized nanostructure at its lowest energy state. A comparison between the calculated lattice parameters and theoretical/experimental results revealed a good agreement. Furthermore, the thermodynamic potentials and specific heat at the constant volume of the nanostructure were calculated. Infrared (IR) and Raman spectra within the frequency range of 0–1000 cm−1 were estimated and assigned, and the results were compared with experimental data and demonstrated good agreement with the literature.