Exchange-correlation Interaction Research Articles

Electronic and optical characteristics of CaLiX3 (X = Cl, Br, I) perovskite compounds using the Tran–Blaha modified Becke–Johnson potential

We present the results of a comprehensive investigation using the full-potential linearized augmented plane wave approach to analyze the structural characteristics, electronic structures, and optical spectra of the perovskite compounds CaLiX3 (X = Cl, Br, or I). Various functionals were employed to simulate the exchange–correlation interactions. The calculated equilibrium structural parameters, obtained using the generalized gradient approximation, are consistent with the existing findings in the literature. The computed electronic structures reveal that the Tran–Blaha modified Becke–Johnson potential significantly enhances the bandgap. For all CaLiX3 compounds studied, we predicted an indirect bandgap. Additionally, we observed a gradual decrease in the bandgap as the atomic size of the X element increases. The electronic states constituting the various energy bands were evaluated by computing the partial and total densities of states. In addition, we computed a variety of optical spectra, including the complex dielectric function, absorption coefficient, refractive index, extinction coefficient, reflectivity, and electron energy loss function. The results demonstrate that a decrease in the bandgap leads to an increase in the zero-frequency limit of the dielectric function ε(0). The origins of the peaks and structures in the optical spectra were identified.

Assessing the viability of hydrogen-based perovskites for optoelectronic and thermoelectric applications via first principle modeling.

In this study, we delve into the physical characteristics of six hydride perovskites of ABH3-type materials (CsCaH3, CsSrH3, KMgH3, LiBaH3, NaBeH3, and RbCaH3). Our investigation primarily focuses on assessing their structural stability by determining the enthalpy of formation and examining the dispersion of phonons. Using band structure calculations, we discern the characteristics of semiconductors, observing a direct bandgap in all four perovskites except NaBeH3 and KMgH3, which exhibit indirect gaps. Among these, NaBeH3 possesses the narrowest gap at 1.91 eV, while the widest gap is observed in the perovskite RbCaH3, measuring 4.56 eV. Furthermore, we conduct a thorough analysis of their optical properties, including parameters such as the real and imaginary dielectric function, absorption coefficient, and refractive index within an energy range of 0 to 14 eV. The results of our study are highly encouraging, suggesting that these materials hold significant promise for utilization in photovoltaic cells. This is primarily attributed to their remarkable ability to absorb light across both the ultraviolet (UV) and visible spectra. Additionally, we conducted an assessment of the thermoelectric properties of the six perovskite materials. RbMgH3 exhibits a maximum Seebeck coefficient (Smax) of 1.5 mV/K, whereas KMgH3 achieves a figure of merit reaching unity. These findings present promising opportunities for utilizing these compounds in thermoelectric devices. In this study, all self-consistent field (SCF) calculations were performed using density functional theory (DFT), employing the FP-LAPW + lo method as implemented in the Wien2k code. The Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation, the modified Becke-Johnson (mBJ) methods, and the HSE06 hybrid functional were employed to characterize the exchange-correlation interactions. Thermoelectric parameters were extracted using the BoltzTraP software.

Band-gap tuning in Mn-doped Er2Ti2O7: Insight from the experimental and theoretical approach

We report the studies of electronic and optical properties of Er2Ti2−xMnxO7 (x = 0, 0.1, & 0.2) through combined theoretical insights from density functional theory (DFT) calculations and experimental approaches, including ultraviolet-visible absorption, photoluminescence emission spectroscopy, and Raman spectroscopy. For quantitatively correct optical bandgaps through DFT calculations, we considered the LDA-1/2 technique for the exchange-correlation interactions. The energy bandgap values obtained using theoretical formulations are in close accordance with the experimental results. The bandgap value obtained using the LDA-1/2 approach indicates the insulated ground state of the Er2Ti2−xMnxO7 (x = 0, 0.1, & 0.2) system. The band gap value obtained experimentally reduces from 3.82 eV to 2.45 eV as the level of Mn doping increases from 0 to 0.2. This reduction in the experimental band gap is attributed to the fact that inclusion of Mn atoms into the crystal lattice alters the electronic structure of the system. Substituting the Mn atom introduces additional electronic states within the band structure, leading to a modification of the band gap. Crystallographic data indicates that inclusion of Mn reduces the Ti-O bond length as in indicated in the table which reduces to 1.939(0) Å for x = 0.2 from 1.947(0) Å for x = 0. This results in the reduction of the extent of hybridization between O-2p and Ti-3d states, thereby reducing the band gap.

Computational investigation of the structural, elastic, electronic, and thermodynamic properties of chloroperovskites GaXCl3 (X = Be, Ca, or Sr) using DFT framework

In this study, we employed the pseudopotential plane wave approach to examine the influence of the X atom (X = Be, Ca, or Sr) on the physical properties of isostructural chloroperovskites GaXCl3. The GGA-PBEsol functional was employed to simulate the exchange–correlation interactions. The computed equilibrium lattice parameters exhibit a high level of concordance with the existing theoretical findings. The cohesion energy and enthalpy of formation were computed to verify the energetic stability of the materials under consideration. The determined values of the single-crystal elastic constants (Cij) indicate that GaBeCl3 remains mechanically stable up to a hydrostatic pressure of 18 GPa. Similarly, GaCaCl3 preserves its stability up to 5 GPa, while GaSrCl3 remains mechanically stable up to 1.25 GPa. The projected Cij values were used to estimate several elastic moduli and related properties, including the shear and bulk moduli, sound wave speeds, Young’s modulus, Poisson’s ratio, and Debye temperature. The energy band structures of the studied compounds, as predicted by the HSE06 functional, demonstrate their wide bandgap semiconductor nature. Specifically, GaBeCl3 demonstrates an indirect bandgap of 3.828 eV, while GaCaCl3 reveals an indirect bandgap of 4.612 eV and GaSrCl3 has an indirect bandgap of 4.405 eV. The quasiharmonic Debye approach was employed to examine various thermal parameters, including the temperature dependence of the unit cell volume, bulk modulus, expansion coefficient, Debye temperature, isochoric and isobar heat capacities, Grüneisen parameter, and entropy function. It has been shown that GaBeCl3 demonstrates a lower thermal expansion coefficient and a higher Debye temperature in comparison to GaCaCl3 and GaSrCl3.

Structural, elastic, electronic, and optical properties of lead-free halide double perovskites Cs2BꞌBꞌꞌBr6 (BꞌBꞌꞌ: BeMg, CdBe, CdGe, GeMg, GeZn, MgZn): Ab initio calculations.

In our study, we theoretically investigated the structural, elastic, electronic, and optical characteristics of halide double perovskites (DPs) Cs2B'B''Br6(B'B'': BeMg, CdBe, CdGe, GeMg, GeZn, MgZn). Structural stabilities were assessed based on the enthalpy of formation, tolerance factor, and elastic constants. Ductile and brittle behavior was examined usingPoissonand Pugh's ratios. Based on electronic calculations, it has been concluded that Cs2B'B''Br6double perovskites with B'B'' as BeMg or CdBe exhibit direct bandgaps, whereas those with B'B'' as CdGe, GeMg, GeZn, or MgZn display indirect bandgaps.Additionally, we thoroughly investigated the optical properties of double perovskites by analyzing all their parameters in the energy range spanning 0 to 13eV.Primary absorption was noted in the ultraviolet (UV) region. In this work, all calculations were performed using the Wien2k package. The generalized gradient approximation (GGA) and the modified Becke-Johnson (mBJ) method were employed to describe the exchange-correlation interactions.

First principle study of scandium-based novel ternary half Heusler ScXGe (X = Mn and Fe) alloys: insight into the spin-polarized structural, electronic, and magnetic properties.

The structural, electronic, and magnetic properties of novel half-Heusler alloys ScXGe (X = Mn, Fe) are investigated using the first principle full potential linearized augmented plane wave approach based on density functional theory (DFT). To attain the desired outcomes, we employed the exchange-correlation frameworks, specifically the local density approximation in combination with Perdew, Burke, and Ernzerhof's generalized gradient approximation plus the Hubbard U parameter method (GGA + U) to highlight the strong exchange-correlation interaction in these alloys. The structural parameter optimizations, whether ferromagnetic (FM) or nonmagnetic (NM), reveal that all ScXGe (where X = Mn, Fe) Heusler alloys attain their lowest ground state energy during FM optimization. The examination of the electronic properties of these alloys reveals their metallic character in both the spin-up and spin-down channels. The projected densities of states indicate that bonding is achieved through the hybridization of p-d and d-d states in all of the compounds. The investigation of the magnetic properties in ScXGe (where X = Mn, Fe) compounds indicates pronounced stability in their ferromagnetic state. Notably, the Curie temperatures for ScXGe (X = Mn, Fe) are determined to be 2177.02 K and 1656.09 K, respectively. The observation of metallic behavior and the strong ferromagnetic characteristics in ScXGe (X = Mn, Fe) half-Heusler alloys underscores their potential significance in the realm of spintronic devices. Consequently, our study serves as a robust foundation for subsequent experimental validation.

The structural and electronic properties of (001) surface of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) with first-principles calculations.

1,3,5-triamino-2,4,6-trinitrobenzene (TATB) is a typical insensitive energetic material. It can be used in explosive formulations, such as PBX-9502 and LX-17-0. TATB is an intriguing and unusual explosive for another reason: it crystallizes into a wide array of planar hydrogen bonds, forming a graphite-like layered structure. Therefore, TATB is one of the important research objects, and its surface structure needs to be deeply understood. In this research work, the electronic and energetic properties of TATB (001) surface are explored. In this paper, the structural, electronic, energetic properties and impact sensitivity of TATB (001) surface structure at 0 and -3 GPa along with x-axis were calculated in this study using the first-principles calculations. The calculations in this paper are performed in the CASTEP code, which is based on the density functional theory with the first-principles calculation method using the plan-wave pseudopotential approach. The exchange-correlation interaction was adopted by the generalized gradient approximation (GGA) with the Perdew-Burke-Ernzerhof (PBE) functional. The DFT-D method with the Grimme correction accurately models van der Waals interactions. To model the surface structures of TATB, the planar slab method was employed. We constructed TATB (001) periodic slabs including three layers with a 15-Å vacuum layer.

First-principle study on the geometric and electronic structure of Mg-doped LiNiO2 for Li-ion batteries.

Ni-rich layered oxides have been widely studied as cathodes because of their high energy density. However, the gradual structural transformation during the cycle will lead to the capacity degradation and potential decay of the cathode materials. In this paper, first-principle calculations were used to investigate the formation energy, and geometric and electronic structure of Mg-doped LiNiO2 cathode for Li-ion batteries. The results show that Mg doping has little effect on the geometric structure of LiNiO2 but has great effect on its electronic structure. Our data give an insight into the microscopic mechanism of Mg-doped LiNiO2 and provide a theoretical reference for experimental research, which is helpful to the design of safer and higher energy density Ni-rich cathodes. In this work, all calculations were performed by the VASP package; the PBE functional in the generalized gradient approximation (GGA) was employed to describe the exchange-correlation interactions. An energy cutoff of 520eV and a 5 × 5 × 3 Monkhorst-Pack mesh of k-point sampling in the Brillouin zone were chosen for all calculations. All atoms were relaxed until the convergences of 10-5eV/f.u in energy and 0.01eV/Å in force were reached.

Physical properties of Be-based fluoroperovskite compounds XBeF3 (X = K, Rb): a first-principles study

In this study, we used the ab-initio computational tools as implemented in the CASTEP code to explore the effects of pressure on the structural, elastic, electronic, thermodynamic and optical properties of the fluoroperovskite compounds XBeF3 (X = K, Rb) based on Being. Exchange–correlation interactions were modeled using the GGA-PBEsol functional. The ground state of the title materials was characterized by calculating the optimized lattice parameter, the bulk modulus B and its pressure derivative, and the Goldsmith tolerance factor. These materials exhibit structural stability in the cubic structure even when subjected to significant pressure levels, extending up to 18 GPa. The analysis of numerical assessments of single-crystal elastic constants (Cij ), polycrystalline elastic moduli, namely shear modulus (G), Young’s modulus and Poisson’s ratio, as well as the anisotropy factor (A), highlights the mechanical stability, elastic anisotropy and ductility of considered the compounds. The thermodynamic properties of these materials were studied through the Debye quasi-harmonic model. Analysis of energy band structures and density of states spectra shows that XBeF3 (X = K, Rb) is insulating in nature, with band gaps of 7.99 and 7.26 eV, respectively. Additionally, we calculated the linear optical spectra, including dielectric function, absorption coefficient, refractive index, optical reflectivity, and energy loss function. Based on the results obtained, these materials could be used in various optoelectronic devices operating in the UV spectrum and in energy storage devices.

Theoretical investigation of adsorption characteristics of typical additives for zinc electroplating.

Electroplated zinc layers have shown excellent corrosion resistance, especially those are stable in the atmosphere after the passivation, and therefore zinc electroplating is widely used in various fields such has mechanical, vehicle, construction, and ironware industries. Benzalacetone (BA) was reported as brighteners for zinc deposition, while polyoxyethylene nonylphenylether (NP) was used as levelers or carriers for zinc electroplating. Sodium benzoate (SB) and dispersant NNO cooperatively act as auxiliary additives. Quantum chemical parameters (QCPs) of four additives were calculated by using DFT, and MD simulations were performed. By comparing binding energies of four additives (benzalacetone (BA), sodium benzoate (SB), polyoxyethylene nonylphenylether (NP) and dispersant NNO), with Zn (001) surface, BA has the lowest binding energy, which is due to the lowest hardness parameter, and NNO has the highest binding energy, which is due to the highest dipole moment despite its small hardness parameter. For DFT calculation, NWChem was employed, which uses the Gaussian basis set. The B3LYP functional was used for exchange-correlation interaction between electrons, and the 6-311G+ (d,p) basis sets were used for all the atoms. Solvation effect was considered by using COSMO (COnductor-like Screening MOdel), in which the dielectric constant of solvent was set to 78.54 of water. For dispersion correction, DFT-D method of Tkatchenko and Scheffler (TS) was used. MD simulations were performed by using GULP (General Utility Lattice Program) code with Dreiding forcefield and atomic Hirshfeld charges from DFT calculations. MD simulations were performed on the conditions of NVT ensemble with a step of 1 fs and simulation time of 500 ps at 298 K and 323 K. To consider solvation effect, 1,000 water molecules were inserted into the box.

Effect of Mn doping on the electronic and optical properties of Dy2Ti2O7: a combined spectroscopic and theoretical study

Electronic and optical studies on Dy2Ti2−Mn x O7 (x = 0.00, 0.05, 0.10, 0.15, & 0.20) have been presented through both, theoretical (density functional theory (DFT) calculations) and experimental (ultraviolet-visible absorption and photoluminescence emission spectroscopy) approaches. DFT calculations were employed considering the local density approximation (LDA) and LDA-1/2 for exchange-correlation interactions. Computed crystallographic parameters and energy band-gap using theoretical formulations are in good agreement with experimental results. The band-gap value obtained through the LDA-1/2 approach indicates insulated ground state of Dy2Ti2−x Mn x O7 (x = 0.00, 0.05, 0.10, 0.15, 0.20) system. Experimentally obtained band gap value reduces from 3.82 eV to 2.45 eV with increase in positive chemical pressure as x increases from 0 to 0.20. Reduction in band gap value is attributed to the fact that there exists a lack of hybridization between the O-2p orbital and Ti-3d orbital, which is well correlated with the crystallographic data. Jahn-Teller effect is likely to be responsible for the presence of a mixed state of Mn (explained using x-ray photoelectron spectroscopy results), resulting in the intermediate Mn state between the valence band and the conduction band with immediate inclusion of Mn at Ti site in Dy2Ti2−x Mn x O7 system.

Structural, elastic, and thermodynamic properties of BaXCl3 (X = Li, Na) perovskites under pressure effect: ab initio exploration

In this study, we employed the ab initio pseudopotential plane wave approach, utilizing the GGA-PBEsol exchange-correlation functional, to investigate the structural, elastic, and thermodynamic properties of BaXCl3 (X = Li, Na) perovskites under hydrostatic pressures ranging from 0 to 18 GPa. Apart from utilizing the GGA-PBEsol functional, this study also employed the GGA-PBE, GGA-WC, and LDA functionals to simulate the exchange-correlation interactions for computing the structural parameters. Our results show that the optimized lattice parameters are in good agreement with previously predicted values. Based on the calculated elastic moduli of a single crystal, we found that both BaLiCl3 and BaNaCl3 perovskites retain mechanical stability under hydrostatic pressures of up to 18 GPa. Furthermore, we calculated several other important parameters that describe the polycrystalline aggregates of these compounds, including the modulus of compressibility, the shear modulus, the Poisson’s ratio, Young’s modulus, the speeds of sound, and the Debye temperature. Additionally, we examined the temperature and pressure dependencies of the thermal coefficients of the perovskites using the quasi-harmonic approximation. Notably, all of the results presented in this study are reported for the first time and require further confirmation through experimental investigations. We hope that our findings contribute to a more comprehensive understanding of the structural and thermodynamic properties of BaXCl3 (X = Li, Na) perovskites under pressure.

The single-atom catalytic activity of the hydrogen evolution reaction of the experimentally synthesized boridene 2D material: a density functional theory study

Previous theoretical studies have suggested that two-dimensional (2D) MBene materials might display adequate monatomic catalytic activity for the hydrogen evolution reaction (HER). Recently, a study reported the experimental synthesis of a 2D MBene (Mo4/3B2), re-defined as boridene, albeit no effort has been devoted to explore the single-atom catalytic activity for HER of this experimentally synthesized 2D material. Therefore, we herein investigate the single-atom HER performance of the boridene. Interestingly, with Mo defects mixed with single Au and Zn atoms shows excellent hydrogen evolution performance, and the change in the Gibbs free energy ([Formula: see text]) value is close to 0eV, which can even match the performance of Pt-based materials. Through analysis of the charge density difference and density of states, the mechanism affecting the HER performance is explained at the electronic level. This work provides a new direction for the use of the Mo4/3B2 monolayer two-dimensional materials in the field of single-atom catalysis for HER. This study used the DFT calculations in Vienna ab initio simulation package. The GGA-Perdew-Burke-Ernzerhof functional with DFT-D2 correction is used to describe the exchange-correlation interactions. The projection augmented wave is used with the plane wave cutoff of 500eV. The convergences of energy and force are 10-5eV and 0.01eV/Å, respectively. A vacuum layer with a height of 20Å is set in the Z direction. For geometry optimization, self-consistent, and DOS calculations, the k-point grids sampled in Brillouin zones are 3 × 3 × 1, 9 × 9 × 1, and 9 × 9 × 1, respectively. The AIMD simulation is performed in the canonical ensemble (NVT), and the temperature was maintained at 300K by Nosé-Hoover thermostats with a time step of 2.0fs.

Acoustic plasmons and isotropic short-range interaction in two-component electron liquids

Dispersion of acoustic plasmons and isotropic Landau parameters are calculated in three- and two-dimensional two-component electron-electron and electron-hole liquids at various concentration and mass ratios using Landau-Silin kinetic equation and the random phase approximation for the self-energy. It is shown that the mode propagation and the strength of quasiparticle interaction are determined by the intercomponent screening and are asymmetric with respect to charge composition of two-component liquid. The well-defined acoustic plasmon-zero sound mode arises at strong difference in concentrations between components and its renormalization by the short-range exchange-correlation interaction is negligible. The acoustic plasmon mediated interparticle effective interaction in the fast component is weak in both the three- and two-dimensional electron liquids with parabolic dispersion, so the associated plasmonic superconductivity and the formation of acoustic plasmarons are unfavorable.

Revisiting the trapping of noble gases (He-Kr) by the triatomic H3+ and Li3+ species: a density functional reactivity theory study.

Small atomic clusters with exotic stability, bonding, aromaticity, and reactivity properties can be made use of for various purposes. In this work, we revisit the trapping of noble gas atoms (He-Kr) by the triatomic H3+ and Li3+ species by using some analytical tools from density functional theory, conceptual density functional theory, and the information-theoretic approach. Our results showcase that though similar in geometry, H3+ and Li3+ exhibit markedly different behavior in bonding, aromaticity, and reactivity properties after the addition of noble gas atoms. Moreover, the exchange-correlation interaction and steric effect are key energy components in stabilizing the clusters. This study also finds that the origin of the molecular stability of these species is due to the spatial delocalization of the electron density distribution. Our work provides an additional arsenal towards a better understanding of small atomic clusters capturing noble gases.

Collective interactions among organometallics are exotic bonds hidden on lab shelves

Recent discovery of an unusual bond between Na and B in NaBH3− motivated us to look for potentially similar bonds, which remained unnoticed among systems isoelectronic with NaBH3−. Here, we report a novel family of collective interactions and a measure called exchange-correlation interaction collectivity index (ICIXC; {ICI}in left[{{{{mathrm{0,1}}}}}right]) to characterize the extent of collective versus pairwise bonding. Unlike conventional bonds in which ICIXC remains close to one, in collective interactions ICIXC may approach zero. We show that collective interactions are commonplace among widely used organometallics, as well as among boron and aluminum complexes with the general formula [Ma+AR3]b− (A: C, B or Al). In these species, the metal atom interacts more efficiently with the substituents (R) on the central atoms than the central atoms (A) upon forming efficient collective interactions. Furthermore, collective interactions were also found among fluorine atoms of XFn systems (X: B or C). Some of organolithium and organomagnesium species have the lowest ICIXC among the more than 100 studied systems revealing the fact that collective interactions are rather a rule than an exception among organometallic species.

The half-metallic properties of Heusler alloys Mn-=SUB=-2-=/SUB=-ScZ (Z=Al, Si, P, Ga, Ge, As, In, Sn, Sb): ab initio study

The properties of Heusler alloys of the Mn2ScZ family (Z=Al, Si, P, Ga, Ge, As, In, Sn, Sb) are investigated within the framework of the density functional theory. The PBE GGA and meta-GGA SCAN functionals were used for approximation of the exchange-correlation interactions. Calculations show that PBE does not predict ideal half-metallic behavior, unlike SCAN. It is shown that at Z=P, Si, a transition from the half-metallic state to the metallic one is observed. This effect can be used to develop tunable spintronic devices. Keywords: exchange-correlation functional, meta-GGA SCAN, half-metal ferromagnets, Heusler alloys.

The half-metallic properties of Heusler alloys Mn-=SUB=-2-=/SUB=-ScZ (Z=Al, Si, P, Ga, Ge, As, In, Sn, Sb): ab initio study

The properties of Heusler alloys of the Mn2ScZ family (Z=Al, Si, P, Ga, Ge, As, In, Sn, Sb) are investigated within the framework of the density functional theory. The PBE GGA and meta-GGA SCAN functionals were used for approximation of the exchange-correlation interactions. Calculations show that PBE does not predict ideal half-metallic behavior, unlike SCAN. It is shown that at Z=P, Si, a transition from the half-metallic state to the metallic one is observed. This effect can be used to develop tunable spintronic devices. Keywords: exchange-correlation functional, meta-GGA SCAN, half-metal ferromagnets, Heusler alloys.

Efficient Electronic Modulation of g-C 3 N 4 Photocatalyst by Implanting Atomically Dispersed Ag 1 -N 3 for Extremely High Hydrogen Evolution Rates

Efficient Electronic Modulation of g-C ₃ N ₄ Photocatalyst by Implanting Atomically Dispersed Ag ₁ -N ₃ for Extremely High Hydrogen Evolution Rates

Low-energy electron diffraction with signal electron carrier-wave wavenumber modulated by signal exchange-correlation interaction

Low-energy electron diffraction (LEED) is considered as elastic electron-atom scattering (EEAS) operating in a target crystal waveguide, where a signal electron carrier wave is wavenumber modulated by signal exchange-correlation (XC) interaction. A carrier potential is designed using a KKR (Korringa-Kohn-Rostoker) muffin-tin (MT) model built on overlapping MT spheres that implement atoms with double degree of freedom, radius and potential level. An XC potential is constructed using Sernelius’s many-particle theory on electron self-energy. EEAS phase shifts are derived from Dirac’s differential equations, and four recent LEED investigations are recalculated: Cu(111) + (3 √ 3 × √ 3)R30° -TMB, TMB = 1,3,5-tris(4-mercaptophenyl)-benzene with chemical formula C24H15S3; Ag(111) + (4 × 4)-O; Ag(111) + (7 × √ 3)rect-SO4; and Ru(0001) + ( √ 3 × √ 3)R30° -Cl. Our EEAS phase shifts generate substantially improved reliability factors, and we report the first confirmation of electron self-energy by LEED experiment.