Generalized Gradient Approximation Research Articles

First-principles study and mesoscopic modeling of two-dimensional spin and orbital fluctuations in FeSe

We calculated the structural, electronic, and magnetic properties of FeSe within density-functional theory at the generalized gradient approximation level. First, we studied how the bandwidth of the d-bands at the Fermi energy is renormalized by adding simple corrections: Hubbard U, Hund's J, and by introducing long-range magnetic orders. We found that introducing either a striped or a staggered dimer antiferromagnetic order brings the bandwidths—which are starkly overestimated at the generalized gradient approximation level—closer to those experimentally observed. Second, for the ferromagnetic, the striped, checkerboard, and staggered dimer antiferromagnetic order, we investigate the change in magnetic formation energy with local magnetic moment of Fe at a pressure up to 6 GPa. The bilinear and biquadratic exchange energies are derived from the Heisenberg model and noncollinear first-principles calculations, respectively. We found a nontrivial behavior of the spin-exchange parameters on the magnetization, and we put forward a field-theory model that rationalizes these results in terms of two-dimensional spin and orbital fluctuations. The character of these fluctuations can be either that of a standard density wave or a topological vortex. Topological vortices can result in mesoscopic magnetization structures. Published by the American Physical Society 2024

Local Density Approximation for Excited States

The ground state of an homogeneous electron gas is a paradigmatic state that has been used to model and predict the electronic structure of matter at equilibrium for nearly a century. For half a century, it has been successfully used to predict ground states of quantum systems via the local density approximation (LDA) of density functional theory (DFT), and systematic improvements in the form of generalized gradient approximations and evolution thereon. Here, we introduce the LDA for excited states by considering a particular class of nonthermal ensemble states of the homogeneous electron gas. These states find sound foundation and application in ensemble DFT—a generalization of DFT that can deal with ground and excited states on equal footing. The ensemble LDA is shown to successfully predict difficult low-lying excitations in atoms and molecules for which approximations based on local spin density approximation and time-dependent LDA fail. Published by the American Physical Society 2024

First-Principles Investigation of Structural, Electronic, Optical, Elastic, and Thermoelectric Properties of Cubic Francifluorite Perovskites FrXF3 (X = Si, Ge, and Sn) for Optoelectronic and Thermoelectric Device Applications

Abstract This study presents the results of first-principles calculations based on Density Functional Theory (DFT) implemented in the Wien2k code, investigating the properties of FrXF3 compounds where B represents Si, Ge, and Sn. Various exchange-correlation functionals, including Generalized Gradient Approximation (GGA) with Perdew-Burke-Ernzerhof (GGA-PBE), Perdew-Burke-Ernzerhof revised for Solids (GGA-PBEsol), Wu-Cohen exchange (GGA-WC), and Modified Becke-Johnson potential (TB-mBJ), were employed to comprehensively analyze the structural, electronic, optical, elastic, and thermoelectric characteristics of these compounds. The analysis of band structures and density of states revealed that all three compounds exhibit semiconducting behavior with direct band gaps, and the band gaps decrease as we move from Si to Sn. The calculated optical properties indicate strong optical responses in the visible to ultraviolet energy range, suggesting potential applications in optoelectronics. Furthermore, the study evaluated the thermoelectric parameters, including thermal and electrical conductivity, power factor, Seebeck coefficient, and figure of merit. The results demonstrate that the FrXF3 compounds possess remarkable thermoelectric potential, indicating their suitability for thermoelectric applications. Overall, this comprehensive investigation provides valuable insights into the structural, electronic, optical, elastic, and thermoelectric properties of FrXF3 compounds, highlighting their potential for various technological applications, particularly in the field of optoelectronics and thermoelectric devices.

Modeling and simulation of the structural, and optoelectronic properties of aluminum trihydride (β-[formula omitted]) for hydrogen storage

Hydrogen is a promising clean energy source, but its storage poses challenges. In this research, we conducted an in-depth study of the structural and optoelectronic properties of the β-AlH3 phase as a potential material for hydrogen storage. Using the density functional theory (DFT)-based Wien2k code, we optimized the structure of β-AlH3. Hydrogen storage properties show that β-AlH3 contains 10.1% hydrogen by weight, which is a significant amount. Electronic properties reveal that this material is a semiconductor with a wide indirect bandgap of 5.947 eV, obtained by the generalized gradient approximation with modified Becke-Johnson correction (GGA-mBJ). The optical response of β-AlH3 to photons with energies from 0 to 10 eV is also examined for a better understanding of this material. β-AlH3 exhibits a static dielectric permittivity value ε1(ω) of 2.1, indicative of its semiconducting nature. The optical conductivity σ1(ω) shows peaks at 7.25 eV and 8.5 eV, while the absorption coefficient α(ω) increases significantly above the band gap of 5.947 eV, with peaks at 7.2 eV and 9 eV. The refractive index n(ω) and extinction coefficient κ(ω) both display notable features at 7.2 eV and 9 eV, reflecting substantial electronic transitions and optical resonances.This research is crucial to understanding how this material can meet the technological demands of hydrogen storage. The results provide valuable insights into the potential of β-AlH₃ within the future energy landscape, highlighting both advances and challenges in this promising field.

Tuning the Electronic Properties of CumAgn Bimetallic Clusters for Enhanced CO2 Activation

The urgent demand for efficient CO2 reduction technologies has driven enormous studies into the enhancement of advanced catalysts. Here, we investigate the electronic properties and CO2 adsorption properties of CumAgn bimetallic clusters, particularly Cu4Ag1, Cu1Ag4, Cu3Ag2, and Cu2Ag3, using generalized gradient approximation (GGA)/density functional theory (DFT). Our results show that the atomic arrangement within these clusters drastically affects their stability, charge transfer, and catalytic performance. The Cu4Ag1 bimetallic cluster emerges as the most stable structure, revealing superior charge transfer and effective chemisorption of CO2, which promotes effective activation of the CO2 molecule. In contrast, the Cu1Ag4 bimetallic cluster, in spite of comparable adsorption energy, indicates insignificant charge transfer, resulting in less pronounced CO2 activation. The Cu3Ag2 and Cu2Ag3 bimetallic clusters also display high adsorption energies with remarkable charge transfer mechanisms, emphasizing the crucial role of metal composition in tuning catalytic characteristics. This thorough examination provides constructive insights into the design of bimetallic clusters for boosted CO2 reduction. These findings could pave the way for the development of cost-effective and efficient catalysts for industrial CO2 reduction, contributing to global efforts in carbon management and climate change mitigation.

Transfer learning for accurate description of atomic transport in Al-Cu melts.

Machine learning interatomic potentials (MLIPs) provide an optimal balance between accuracy and computational efficiency and allow studying problems that are hardly solvable by traditional methods. For metallic alloys, MLIPs are typically developed based on density functional theory with generalized gradient approximation (GGA) for the exchange-correlation functional. However, recent studies have shown that this standard protocol can be inaccurate for calculating the transport properties or phase diagrams of some metallic alloys. Thus, optimization of the choice of exchange-correlation functional and specific calculation parameters is needed. In this study, we address this issue for Al-Cu alloys, in which standard Perdew-Burke-Ernzerhof (PBE)-based MLIPs cannot accurately calculate the viscosity and melting temperatures at Cu-rich compositions. We have built MLIPs based on different exchange-correlation functionals, including meta-GGA, using a transfer learning strategy, which allows us to reduce the amount of training data by an order of magnitude compared to a standard approach. We show that r2SCAN- and PBEsol-based MLIPs provide much better accuracy in describing thermodynamic and transport properties of Al-Cu alloys. In particular, r2SCAN-based deep machine learning potential allows us to quantitatively reproduce the concentration dependence of dynamic viscosity. Our findings contribute to the development of MLIPs that provide quantum chemical accuracy, which is one of the most challenging problems in modern computational materials science.

First-principle’s calculations to investigate structural, electronic, mechanical, optical, and thermoelectric properties of halide double perovskites K2InScX6 (X = Cl, Br, and I) for thermoelectric and optoelectronic applications

Physical properties of double perovskites K2InScX6 (X = Cl, Br, and I) are investigated using density functional theory (DFT) with generalized gradient approximation (GGA) and perdew-burke-ernerhof (PBE) exchange co-relational functional. Structural stability is confirmed through geometry optimization. Band gaps are calculated using Trans Blaha-modified Becke-Johnson (TB-mBJ) potential and GGA-PBE methods. The obtained band gaps have direct nature. The structural stability has also been confirmed by calculating enthalpy formation (ΔHf), cohesive energy (Ecoh), stiffness coefficients (Cij), tolerance (τG) and octahedral factor (µ). Two materials K2InScCl6, and K2InScBr6 are ductile and one is K2InScI6 brittle. The optical parameters inferred that the maximum absorption of photon energy lies within the visible and ultraviolet regions enabling their use in UV photodetectors and optoelectronics, where light absorption is important for performance. The thermoelectric (TE) parameters like Seebeck coefficient, thermal and electrical conductivity, carrier concentration, power factor and figure of merit ZT parameters are calculated and ZT values are 0.75, 0.94, and 0.91 for K2InScCl6, K2InScBr6, and K2InScI6 at room temperature. These results enable the development of more stable, and high-conversion efficiency devices for TE applications such as thermo-electric power generators.

Computational insights into transition metal-based BaCoX3 (X = Cl, Br, I) halide perovskites for spintronics, photovoltaics, and renewable energy devices

Ab-initio simulations using density functional theory (DFT) were employed to investigate the structural, mechanical, electronic, magnetic, optical, and thermoelectric properties of halide perovskites \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {BaCoX}_3$$\\end{document} (X = Cl, Br, I). Structural optimization and mechanical stability assessments confirm the reliability of these perovskites in a hexagonal P\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$6_3$$\\end{document}mc symmetry. The stability of the ferromagnetic phase was validated through total crystal energy minimization via Murnaghan’s equation of state. Electronic band structures and density of states, derived from the generalized gradient approximation (GGA), reveal a semiconducting ferromagnetic nature in the spin up channel, spotlighting their potential in semiconductor spintronic applications. Phonon dispersion analysis of \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {BaCoCl}_3$$\\end{document} and \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {BaCoBr}_3$$\\end{document} revealed positive phonon modes throughout the entire Brillouin zone, confirming their dynamical stability. In contrast, \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {BaCoI}_3$$\\end{document} demonstrated dynamical instability. The elastic constants confirm the mechanical stability and ductile nature of the perovskites. Optical and dielectric properties of these perovskites show significant UV absorption and photoconductivity, making them highly suitable for optoelectronic and solar cell applications. Finally, transport properties, such as the Seebeck coefficient, electrical conductivity, thermal conductivity, power factor, and figure of merit (ZT) unveil their exceptional thermoelectric performance. Combining half-metallic ferromagnetic traits with superior thermoelectric and optoelectronic performance positions \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {BaCoX}_3$$\\end{document} compounds as exceptional candidates for applications in spintronics, optoelectronics, and thermoelectrics. This comprehensive investigation demonstrates their ability to excel across a diverse array of advanced technological applications.

First principle study of structural and optoelectronic properties of ZnLiX3 (X = Cl or F) perovskites

The zinc-based perovskites ZnLiX3 (X = Cl or F) were investigated for their structural, electronic, and optical properties using the WIEN2k package within density functional theory (DFT). Structural properties were calculated using the generalized gradient approximation (GGA), while the modified Becke-Johnson (mBJ) potential was applied for a more accurate description of the optical and electronic properties. Both compounds are confirmed to be stable, crystallizing in the cubic Pm-3 m (No. 221) space group. ZnLiCl3 has an indirect band gap of 0.30 eV between the Γ and M symmetry points, indicating semiconducting behaviour, while ZnLiF3 exhibits an indirect band gap of 5.45 eV, typical of an insulating material. The electronic states contributing to the band structure were analyzed using the total density of states (TDOS) and partial density of states (PDOS). Optical properties, evaluated in the energy range of 0–14 eV, reveal strong optical conductivity and absorption at higher energies, while both materials show transparency to lower-energy photons. These findings suggest that ZnLiCl3 and ZnLiF3 are suitable candidates for high-frequency UV optoelectronic device applications.

First-principle study origin of ferromagnetism in non-magnetic perovskite BaSnO3 doped with 2p-X (X=C, N)

In this study, our goal is to analyze the origin of magnetization in non magnetic cubic structure perovskite BaSnO3 doped with 2p-X (X=C, N) using the full potential linearized augmented plane wave (FP-LAPW) method based on density functional theory (DFT). For the exchange and correlation potential we have applied the generalized gradient approximation (GGA) and the GGA plus-modified Becke-Johnson potential (mBJ-GGA). The results show that BaSnO3 doped with C then with N and finally with C and N exhibit half-metallic ferromagnetism behavior with the integer magnetic moment of 1, 2 and 3 μB per cell respectively. The origin of the ferromagnetism that occurs within these compounds is mainly caused by the p-p hybridization between 2p-impurities and its neighboring oxygen atoms. These results allowed to conclude that doped perovskite could provide a new type of materials, called half-metallic for future spintronic devices.

The Structural, Elastic, and thermodynamic properties of Sr2P7Br Double Zintl salt with heptaphosphanortricyclane configuration

We investigated the effects of externally applied pressure on the Sr2P7Br compound’s properties, specifically its crystalline structure, elasticity, and thermodynamics. This investigation was carried out using the pseudopotential plane wave method within the framework of density functional theory. We used the well-known PBEsol variant of the exchange–correlation general gradient approximation specifically designed for solid-state analysis. This is the first endeavor to investigate the effects of pressure on the Sr2P7Br material using a theoretical approach. The computed equilibrium structural parameters closely match the relevant experimental counterpart values. The determined elastic constants, obtained under both ambient pressure and hydrostatic pressures up to 18 GPa, satisfy the mechanical stability requirements. Based on the computed Pugh’s ratio, Cauchy pressure, and Poisson’s ratio, it can be concluded that the Sr2P7Br compound exhibits ductile behavior. The polycrystalline elastic moduli, including the isotropic bulk modulus, shear modulus, Young’s modulus, and Poisson’s ratio, at ambient pressure and under pressure effects, were derived from the single-crystal elastic constants. Additionally, associated parameters, such as average sound velocity, Debye temperature, minimum thermal conductivity, and Vickers hardness, were examined under pressure influences. The quasi-harmonic Debye approximation was used to investigate the relationship between temperature and some macroscopic physical parameters, such as lattice parameter, bulk modulus, Debye temperature, volume thermal expansion coefficient, and isobaric and isochoric heat capacities, at fixed pressures of 0, 4, 8, 12, and 16 GPa. The results derived from the elastic constants exhibit substantial concordance with those computed using the Debye quasi-harmonic model, thereby validating the reliability of our findings.

Scrutinizing the electronic structure, magnetic, mechanical, thermodynamic, optical and thermoelectric properties of lead-free hafnium based Hf2VP (P = Si, Sn) full Heusler alloys

The study of energy harvesting and thermoelectric materials has drawn more attention in the last several years. The great thermal stability of these materials is advantageous for thermoelectric devices, in addition to their structural capacity for showcasing and incorporating diverse novel concepts to augment the thermoelectric figure of merit. In the current study, we have predicted the physical properties of Hf2VP (P = Si, Sn) Heuslers using density functional theory in conjunction with the Boltzmann transport scheme. The strength and ductility of these materials are ascertained by simulating elastic characteristics The exchange correlation potential is handled via the modified Becke–Johnson potential (mBJ) and the generalized gradient approximation of Perdew, Burke, and Ernzerhof (GGA-PBE). Near the Fermi level, the band profiles for Hf2VSi and Hf2VSn Heuslers were found to be n-type indirect band-gap respectively. The thermodynamic stability of these materials is approved by the formation and cohesive energy. The relationships between different transport parameters are predicted using the band occupation and density of states in the post DFT treatment. Slack’s equation has identified the most significant lattice component of heat conductivity with great precision. These materials are likely to find use in the design of memory devices and future thermoelectric and energy harvesting materials due to their half-metallic nature and efficient thermoelectric parameters, such as electrical conductivity, Seebeck coefficient, thermal conductivity, power factor, and ZT.

Tuning the Electronic Bandgap of Penta-Graphene from Insulator to Metal Through Functionalization: A First-Principles Calculation.

We performed first-principles density functional theory (DFT) calculations to numerically investigate the electronic band structures of penta-graphene (PG), a novel two-dimensional carbon material with a pentagonal lattice structure, and its chemically functionalized forms. Specifically, we studied hydrogenated PG (h-PG), fluorinated PG (f-PG), and chlorinated PG (Cl-PG). We used the generalized gradient approximation (GGA) and the hybrid Heyd-Scuseria-Ernzerhof (HSE06) exchange-correlation functional in the DFT-based software VASP to capture electronic properties accurately. Our results indicate that hydrogenation and fluorination increased the indirect bandgap of PG from 3.05 eV to 4.97 eV and 4.81 eV, respectively, thereby effectively transforming PG from a semiconductor to an insulator. In contrast, we found that chlorination closed the bandgap, thus indicating the metallic behavior of Cl-PG. These results highlight the feasibility of tuning the electronic properties of PG through functionalization, offering insight into designing new materials for nanoelectronic applications.

A combined approach for comprehensive explanation of defects' thermodynamics in highly non-stoichiometric oxides: Case of RBaCo2O6-δ family (R = La, Nd, Pr, Sm, Gd, Eu, Ho and Y)

The thermodynamics of defect formation in layered perovskite-like cobaltites RBaCo2O6-δ (R = La, Nd, Pr, Sm, Gd, Eu, Ho and Y) was investigated via two distinct methods – (I) processing experimental data on oxygen non-stoichiometry using a quasichemical model and (II) employing a combined approach within the framework of density functional theory (DFT) under general gradient (GGA) and quasiharmonic Debye (QHDA) approximations. The outcomes of the first-principles calculations exhibit a plausible agreement with the fitting results, thereby confirming the validity of the developed model. The study reveals that key thermodynamic parameters governing defect formation, such as the enthalpy and entropy of oxygen exchange, as well as the enthalpy of oxygen disordering over nonequivalent crystallographic positions, exhibit correlations with the size of the rare-earth element R. In contrast, the enthalpy of charge disproportionation is demonstrated to be independent of the nature of the R atom. In Addition, it is suggested that when R = Eu, partial reduction of the latter may be observed in the lattice of EuBaCo2O6-δ. The findings indicate that, at a first approximation, the parameters of defect formation in RBaCo2O6-δ remain relatively independent on temperature and oxygen non-stoichiometry δ. The employed combined approach has been demonstrated to be reliable for assessing the thermodynamic functions of defect formation at elevated temperatures.

Scalar and vectorized implementations of the density functional theory via Geant4 and GeantV project

In this paper, we present the implementation of the Density Functional Theory (DFT) method using the Geant4-DNA framework in the Single Instruction Single Data (SISD) mode. Furthermore, this implementation is improved in terms of execution time within the GeantV project with vectorization techniques such as Single Instruction Multiple Data (SIMD). Within this framework, a set of SIMD strategies in molecular calculation algorithms such as one-electron operators, two-electron operator, quadrature grids, and functionals, was implemented using the VecCore library. The applications developed in this work implement two DFT functionals, the Local Density Approximation (LDA) and the General Gradient Approximation (GGA), to approximate the molecular ground-state energies of small molecules and amino acids. To assess the performance of the implementations, a standard test simulation was performed in multiple CPU platforms. The SIMD vectorization strategy significantly accelerates DFT calculations, leading to time ratios ranging from 1.6 to 5.4 in either individual steps or entire implementations when compared with the scalar process within Geant4.

Enhancement of sodium ion conductivity in phosphate-based glass-ceramics by chemical substitution approach

A NASICON-type sodium-ion conducting material was synthesized via the glass-ceramic route by investigating the zinc doped Na2O–Al2O3–TiO2–P2O5 system. The glasses and glass-ceramics corresponding to the formula Na2+xAl1-xZnxTi(PO4)3 (x = 0, 0.2, 0.4, 0.6, 0.8, 1), labeled as (NAZTP-Gx) and (NAZTP-GCx) respectively, were characterized using different techniques. Differential Scanning Calorimetry (DSC) measurements were carried out to identify the characteristic temperatures, the glass transition (Tg) and the crystallization temperature (Tc). X-ray Diffraction (XRD) analysis of the glass-ceramics confirmed the formation of a solid solution Na2+xAl1-xZnxTi(PO4)3 NASICON phase, Theoretical calculations employing the Perdew–Burke–Ernzerhoff generalized gradients approximation (PBE-GGA) model supported the potential substitution of aluminum by zinc in the octahedral site in the NASICON-phase. Further structural insights were obtained through Infrared (IR) and Raman spectroscopies. Scanning electron microscopy (SEM) analysis revealed a distinct flower-like shape of the formed crystallites in the glass-ceramic NAZTP-GC0.2. Electrical characterization using electrochemical impedance spectroscopy (EIS) demonstrated that the NAZTP-GC0.2 sample exhibited the highest ionic conductivity at 300 °C, reaching 4.1 × 10−5 (Ω−1 cm−1) with an activation energy of 0.25 eV. The DC polarization was performed on the NAZTP-GC0.2 glass-ceramic, revealing that the ions are the main charge carriers in the sample. This comprehensive analysis provides valuable insights into the partial zinc doping of NASICON glass-ceramics, offering potential for improved performance as solid electrolytes in various applications.

Pressure induced tunable physical properties of cubic KHgF3 fluoro-perovskite: A first principle study

The structural, electronic, optical, mechanical, and thermodynamic properties of KHgF3 perovskite under various hydrostatic pressures are examined in this study in the frameworkof Density Functional Theory (DFT) with the Generalized Gradient Approximation (GGA) Perdew-Burke-Ernzerhof (PBE) exchange–correlation function. Tunable physical properties have been observed in KHgF3 as pressure is incrementally applied. The investigated compound displays mechanical instability beyond the pressure range of 0 to –10 GPa, as confirmed by the elastic constant analysis. Under ambient pressure, the lattice constants of KHgF3 closely align with theoretically calculated values, affirming the accuracy of this investigation. In addition, the bandgap of KHgF3 narrows with increasing pressure, facilitating easier electron transition from the valence band to the conduction band. The study reveals that when subjected to different hydrostatic pressures, fluctuations are observed in the peaks of the conductivity spectrum, loss spectrum, and absorption spectrum, particularly shifting towards higher photon energies, as analyzed through the optical properties. Moreover, KHgF3 exhibits ductile behavior at 0 GPa pressure, and this ductility rises with pressure. Thermodynamic analysis reveals a decrease in Debye temperature with increasing pressure, while the melting temperature rises correspondingly. The findings of this investigation also imply that KHgF3 can be a good candidate for optoelectronic device application under different hydrostatic pressures.

Biaxial and Uniaxial Strain Effect on Structural and Electronic Properties of Anatase TiO<sub>2</sub>: A First-Principle Calculation

The effect of biaxial and uniaxial strains on the electronic structure of anatase is studied using Density Functional Theory (DFT) calculation with ultrasoft pseudopotential and a generalized gradient approximation (GGA) Perdew-Burke Ernzerhof (PBE) exchange-correlation. The lattice constant is optimized using the Birch-Murnaghan equation of states (BM-EOS) to get an optimized geometric structure of anatase TiO2. We apply biaxial and uniaxial strains to this optimized structure up to 16% and find that the applied strains change the band gap energy compared to a pure anatase with a different band gap energy up to 1.61 eV for biaxial strain and 0.35 eV for uniaxial strain. The biaxial strains increase gap energies except at +16% tensile strain, decreasing the gap energy to 0.04 eV. Uniaxial strains tend to increase as the strains increase except at-12 and-16%; their gap energy differences are 0.08 and 0.20 eV, respectively, smaller than that of the zero strain. The results also show that the applied 16% tensile strain significantly lengthens the atomic bonds; thus, we conclude that the maximum strain applied to anatase TiO2 is 16%.

Impact of Calcium Doping on the Electronic and Optical Characteristics of Strontium Hydride (SrH2): A DFT Study

This study investigates the electronic and optical properties of calcium-doped strontium hydride (SrH2) using first-principles density functional theory (DFT) calculations via the CASTEP code with generalized gradient approximation (GGA). We explore the impact of calcium (Ca) doping on the electronic band structure, density of states (DOS), and optical absorption spectra of SrH2. Our results show that Ca doping significantly alters the electronic properties of SrH2, notably increasing the indirect bandgap from 1.3 eV to 1.6 eV. The DOS analysis reveals new states near the Fermi level, primarily from Ca 3d orbitals. Moreover, the optical absorption spectra display enhanced absorption in the visible range, suggesting the potential for optoelectronic applications. This research highlights the feasibility of tuning the electronic and optical characteristics of SrH2 through Ca doping, thus opening the way for the generation of advanced materials with tailored properties.

Half-Metal Ferromagnetism V-Doped GaN Nanosheet Application in Spintronic Device

The density functional theory calculations using general gradient approximation (GGA) have been systematically performed to study the electronic structures, the density of states (DOS), and magnetic properties of V-doped GaN nanosheet for different dopant concentrations (2.08% and 4.16%). We conducted the entire study using the Atomistixtool kit code. The electronic properties were improved with the Hubbard values U = 4 eV. V-doped CaN nanosheet exhibits stable ferromagnetic (FM) states relative to corresponding antiferromagnetic (AFM) states. The calculated TC with the V-doping is found to be above the room temperature (RT) one. Calculation results reveal that V-doped nanosheets may be a good candidates for spintronics due to its good half-metal ferromagnetism.