Vienna Ab Initio Simulation Package Research Articles

Pressure effects on the structural, electronic, elastic, optical, and vibrational properties of YMg intermetallic compounds: a first-principles study

The properties of YMg in B2 structure have been comprehensively analysed using the first-principles plane-wave pseudopotential method. Specifically, the structural, electronic, elastic, vibrational, and optical properties were investigated using the generalized gradient approximation (GGA) method in the context of density functional theory. The Vienna ab initio simulation package (VASP) was utilized for these calculations. The computed lattice parameter (3.803 Å) and bulk modulus (41.33 GPa) are consistent with the earlier data on ambient pressure. The electronic band structure and energy-dependent density of states reveal the metallic nature of the titled compounds. The Born stability requirements confirmed the mechanical stability. The analysis of Pugh’s and Poisson’s ratios and Cauchy’s pressure reveals that YMg is ductile under the pressures in consideration. According to several anisotropy indices, the compound is noticeably anisotropic both in ambient and under pressure. Our investigation includes an analysis of several fundamental mechanical parameters of the material, including the bulk modulus, the pressure derivative of the Zener anisotropy factor, Poisson’s ratio, isotropic shear modulus and Young’s modulus with a particular focus on their dependence on pressure. We have determined that the elastic constants obtained remain mechanically stable, satisfying the Born Stability conditions even at high pressures of up to 60 GPa. To explore the dynamic stability of YMg, we analysed the material’s phonon dispersion curves. The examined compound displays stability under dynamic conditions from 0 GPa to 30 GPa, as evidenced by its positive vibration frequencies. However, this stability is not sustained under higher pressure, as the compound becomes unstable after 30 GPa to 70 GPa. The electronic band structure and density of states diagrams demonstrate YMg’s metallic properties. At atmospheric pressure (0 GPa), the total density of states (TDOS) near the Fermi level is approximately 1.63 states/eV, with pressure application reducing DOS. The dielectric function, refractive index, and energy loss spectra are examined within the 0–20 eV energy range. YMg exhibits its highest absorption between 4 and 11 eV. The peak optical conductivity is observed around 0.78 eV (equivalent to 1589.5409 nm), while the most significant energy loss occurs at 11.90 eV, roughly corresponding to 2.8 Hz in the ultraviolet spectrum. Moreover, we extensively analyzed the material’s phonon thermodynamic and optical properties, providing insights into its behavior under various conditions. The outcomes acquired at zero pressure are generally coherent with the current theoretical values.

Establishing the NiMo6Se8 Chevrel Phase as a Promising Material Using DFT

AbstractIn this study, the NiMo6Se8 Chevrel phase is analyzed using Density Functional Theory (DFT) and the Vienna Ab‐initio Simulation Package (VASP). The analysis focuses on the phase's structural, electrical, and mechanical characteristics to fill gaps in the current literature. The presence of a rhombohedral crystal structure confirms its thermodynamic stability, as indicated by a negative formation enthalpy, which suggests that it can be synthesized under favorable conditions. The electronic properties of the phase are analyzed, indicating that it exhibits semiconductor characteristics with a bandgap of 1.07 eV. This makes it appropriate for various technological applications. The estimated elastic constants provide an indication of mechanical strength and flexibility, with a noticeable presence of anisotropic elasticity. The confirmation of dynamical stability is achieved by analyzing the phonon dispersion curve, which reveals the absence of any negative frequencies. Furthermore, the material has a low thermal conductivity, increasing its suitability for thermoelectric applications. The analysis emphasizes the versatile capabilities of the NiMo6Se8 Chevrel phase, especially in thermoelectric and energy storage applications, showcasing its promising potential for future technological implementation.

Thermoelectric properties and thermal transport in two-dimensional GaInSe3 and GaInTe3 monolayers: A first-principles study

We here report the electronic structure calculation of GaInSe3 and GaInTe3 monolayers with the P3m1 (no. 156) space group. The electronic structure and thermoelectric properties of the monolayers are calculated through the Vienna Ab initio Simulation Package and BoltzTraP2 codes. The dynamic and thermodynamic stabilities were verified by calculating their phonon spectra and simulating ab initio molecular dynamics. The monolayers were found to have a direct bandgap, with both PBE + SOC and HSE06 + SOC potentials. The lattice thermal conductivity of GaInTe3 monolayer calculated using Phono3py code shows ultra-low values due to enhanced phonon–phonon scattering. Combining electrical and thermal transport, the values have been evaluated. Importantly, the p-type GaInTe3 has excellent thermoelectric properties at 700 K, with a zT value of 2, indicating that the p-type GaInTe3 has potential application in the field of thermoelectricity.

Enhanced response characteristics of NO2 gas sensor based on ultrathin SnS2 nanoplates: Experimental and DFT study

Layered-metal dichalcogenides with extraordinary characteristics of vast surface area, tunable bandgap and superior adsorption capability enable the potential for application in gas sensors. However, the synthesis of effective material for enhanced response performance remains a challenge. Herein, we exploited a fascinating sensitivity and selectivity towards NO2 gas detection using SnS2 nanoflakes prepared via the hydrothermal method. SnS2 nanoflakes with a thickness of 25 nm and an average diameter of approximately 500 nm show the potential for the detection of NO2 gas at low concentrations of ppb levels. The sensing properties of the SnS2 sensors were investigated for different concentrations of NO2 at various operating temperatures. The sensor exhibits the highest gas-sensing response of 161 at 250 οC upon exposure to 5 ppm of NO2 gas with fast response and recovery times. In addition, the sensor shows excellent selectivity with a low detection limit of ppb level. The electronic structure and gas-sensing mechanism are elucidated via finding density of states, charge density, and band structure based on DFT study which is calculated by the Vienna ab-initio simulation package (VASP). The considerable small adsorption energy reveals a physisorption of the NO2 molecules on the SnS2 surface (-0.174 eV), indicating the SnS2 nanoflakes are intriguing candidates for the speedy detection of NO2 gas.

Energy efficiency and performance analysis of a legacy atomic scale materials modeling simulator (VASP)

AbstractThis work tackles the performance and energy consumption analysis of a legacy scientific application, the VASP (Vienna Ab-initio Simulation Package), an application commonly used by physicists and chemists for modeling materials at the atomic scale. Many of these scientific applications have been implemented in Fortran, where energy metrics instrumentation is not straightforward. We obtained performance figures (execution time and energy consumption) by instrumenting the source code using EML. This energy measurement library has been modified to introduce Fortran interfaces for these metrics. The analysis was carried out using different matrix algebra libraries, parallelization techniques, and hardware platforms, emphasizing on the MPI, OpenMP, and CUDA parallel implementations of the algorithms used in VASP. We employ various material specifications (atomic structures) and molecular sizes of a silicon-based crystal to create a set of benchmarks for these specifications, leading to some recommendations for final users regarding performance improvements. The proposed benchmarking technique assists the user in selecting the right combination of problem size, compilers, and parallelization options available in VASP. For a given system platform, the user will be able to determine not only the architecture to use (GPU or multicore processors), but also the appropriate library and parallelization according to the atomic structure and molecular size.

Precipitation and growth mechanism of TiN on Y2O3 (110) and (100) surfaces of yttrium-containing T4003 stainless steel

The Y2O3/TiN interface of main complex inclusions in T4003 stainless steel with rare earth element Yttrium (Y) content of 0.014 wt% was studied. The chemical composition and morphology of composite inclusions were characterized by scanning electron microscope (SEM) and X-ray energy dispersive spectrometer (EDS), the formation process of Y2O3/TiN composite inclusions was calculated by the first-principles calculations of the Vienna Ab-initio Simulation Package (VASP). Compared with Fe matrix, TiN is more likely to grow in an uneven state, and tends to exist in stainless steel in the form of Y2O3(100)/TiN(110). The main reason for the stability of the interface system is that the p orbitals of the O atoms at the interface forms covalent bonds with the d orbitals of the Ti atoms. It provides a new idea for improving the properties of stainless steel effectively by using heterogeneous nucleation of inclusions in steel.

Atomic Diffusivities of Yttrium, Titanium and Oxygen Calculated by Ab Initio Molecular Dynamics in Molten 316L Oxide-Dispersion-Strengthened Steel Fabricated via Additive Manufacturing.

Oxide-dispersion-strengthened (ODS) steels have long been viewed as a prime solution for harsh environments. However, conventional manufacturing of ODS steels limits the final product geometry, is difficult to scale up to large components, and is expensive due to multiple highly involved, solid-state processing steps required. Additive manufacturing (AM) can directly incorporate dispersion elements (e.g., Y, Ti and O) during component fabrication, thus bypassing the need for an ODS steel supply chain, the scale-up challenges of powder processing routes, the buoyancy challenges associated with casting ODS steels, and the joining issues for net-shape component fabrication. In the AM process, the diffusion of the dispersion elements in the molten steel plays a key role in the precipitation of the oxide particles, thereby influencing the microstructure, thermal stability and high-temperature mechanical properties of the resulting ODS steels. In this work, the atomic diffusivities of Y, Ti, and O in molten 316L stainless steel (SS) as functions of temperature are determined by ab initio molecular dynamics simulations. The latest Vienna Ab initio Simulation Package (VASP) package that incorporates an on-the-fly machine learning force field for accelerated computation is used. At a constant temperature, the time-dependent coordinates of the target atoms in the molten 316L SS were analyzed in the form of mean square displacement in order to obtain diffusivity. The values of the diffusivity at multiple temperatures are then fitted to the Arrhenius form to determine the activation energy and the pre-exponential factor. Given the challenges in experimental measurement of atomic diffusivity at such high temperatures and correspondingly the lack of experimental data, this study provides important physical parameters for future modeling of the oxide precipitation kinetics during AM process.

ElasTool v3.0: Efficient computational and visualization toolkit for elastic and mechanical properties of materials

Efficient computation and visualization of elastic and mechanical properties are crucial in the selection of materials and the design of new materials. The ElasTool v3.0 toolkit marks a significant advancement in the computational analysis and visualization of elastic and mechanical properties of materials, essential in material selection and design. This enhanced version extends beyond standard calculations like elastic tensor, Young's modulus, bulk modulus, and Poisson's ratio. It introduces capabilities for computing minimum thermal conductivity, linear compressibility, rendering the Christoffel equation, and elastic energy density. Notably, it integrates advanced visualization tools, including compatibility with Plotly and Elate web platforms for interactive web-based property exploration. A key feature of ElasTool v3.0 is the implementation of second-order elastic constants (SOECs) for tubular 2D-based nanostructures and nanotubes. Leveraging high-efficiency strain-matrix sets (OHESS), the toolkit now facilitates efficient computation of elastic constants and mechanical properties at both zero and finite temperatures for 1D, 2D, and 3D dimensions. ElasTool is openly accessible on GitHub: https://github.com/elastool. Program summaryProgram Title: ElasTool v3.0CPC Library link to program files:https://doi.org/10.17632/9hpgmspfmk.1Licensing provisions: GNU General Public License, version 3Programming language: Python 3Nature of problem: A computational toolkit that can efficiently compute the elastic and mechanical properties of materials using ab initio methods and provide advanced visualization capabilities is crucial to accurate material analysis.Solution method:ElasTool addresses this need by incorporating high-efficiency strain-matrix sets that require only small strain sets with ab initio methods such as density functional theory and molecular dynamics. This package is versatile and adept at calculating elastic constants for both 2D and 3D structures, including tubular 2D-based nanostructures and nanotubes and 1D nanoribbons at zero and finite temperatures. Beyond basic elastic moduli, ElasTool now boasts advanced visualization capabilities and computes additional critical properties such as minimum thermal conductivity, elastic energy density, and linear compressibility. This enhancement transforms ElasTool into a comprehensive tool for accelerated material design and modeling, and advanced visualization, offering both efficiency and depth in material property analysis.Additional comments including restrictions and unusual features:ElasTool is currently integrated with the Vienna Ab initio Simulation Package (VASP). Adapting to other electronic structures is straightforward.ElasTool offers serial and parallel execution. Depending on the system size, the number of strains, the nature of the calculations (zero or finite temperature), and the computing architecture, the computing time can vary from a minute to as long as 15 hours.

Tritium storage and release mechanism in nuclear graphite using first-principles combined thermal desorption theory

Nuclear graphite (NG) is widely applied in nuclear facilities, and its strong interaction with tritium is an essential factor for tritium transport behavior in various reactors and the treatment of radioactive NG waste. Given that NG is a polycrystalline and porous material, interactions between tritium and NG exist in various microstructures, including graphite edges, graphene basal planes, and amorphous structures. In this study, density functional theory which is integrated in Vienna ab initio simulation package (VASP) was combined with thermal desorption theory to elucidate the underlying mechanism of hydrogen isotope storage corresponding to the experimentally observed desorption peaks in NG. The four desorption temperature peaks, ranging from low to high, were mainly attributed to hydrogen isotope desorption from the graphite basal plane surface, amorphous carbon surface, unsaturated armchair and zigzag edges, respectively. The interaction between hydrogen isotopes and carbon nanostructures provides deeper insights into the understanding of tritium enrichment on the NG surface, which is primarily attributed to the adsorption of tritium on graphite basal plane-like surfaces at relatively low temperatures. This study provides a practical method to bridge the gap between the atomic binding structure and desorption temperature peaks from a kinetic perspective, providing insights into temperature-dependent hydrogen desorption in typical carbon structures and deepening our understanding of tritium transport behaviors in advanced nuclear energy systems.

Adsorption of N, He and Ne on CGe nanoribbons for sensing and optoelectronic applications.

Research into nanomaterials yields numerous exceptional applications in contemporary science and technology. The subject of this investigation is a one-dimensional nanostructure, six atoms wide, featuring hydrogen-functionalized edges. The theoretical foundation of this study relies on Density Functional Theory (DFT) and is executed through the utilization of the Vienna Ab initio Simulation Package (VASP). The outcomes demonstrate the stability of adsorption configurations, along with the preservation of a hexagonal honeycomb lattice. The pristine configuration, characterized by a wide bandgap, is well-suited for optoelectronic applications, whereas adsorption configurations find their application in gas sensing. Nitrogen (N) adsorption transforms the semiconducting system into a semimetallic one, with the spin-up state showing semiconductor characteristics and the spin-down state exhibiting metallic attributes. The intricate multi-orbital hybridization is explored through the analysis of partial states. While the pristine system remains non-magnetic, N adsorption introduces a magnetic moment of 0.588 μB. The examination of charge density differences indicates a significant charge transfer from N to the CGe substrate surface. Optical properties are systematically investigated, encompassing the dielectric function, absorption coefficient and electron-hole density. Notably, the real part of the dielectric function exhibits negative values, a result that holds promise for future communication applications.

C, Ge-doped h-BN quantum dot for nano-optoelectronic applications

Emerging materials, particularly nanomaterials, constitute an enduring focal point of scientific inquiry, with quantum dots being of particular interest. This investigation is centered on elucidating the exceptional structural, electromagnetic, and optical characteristics of hexagonal boron nitride (h-BN) quantum dots and h-BN quantum dots doped with carbon (C) and germanium (Ge). The employed methodology in this study hinges on density functional theory coupled with the Vienna Ab initio simulation package. The outcomes of this research unveil the structural stability of hexagonal honeycomb structures upon optimization. Comprehensive examinations encompassing structural properties, electromagnetic characteristics, and charge density variations have been systematically conducted. Furthermore, this work delves into the elucidation of multi-orbital hybridizations that give rise to σ bonds and π bonds. Notably, the outcomes of the optical property analysis divulge intriguing observations. Specifically, the absorption coefficient exhibits zero values within select energy ranges within the visible light spectrum, a phenomenon observed in both pristine and C-doped configurations. This discovery underscores the material’s optical transparency at these specific radiation energies. Additionally, the 0x and 0y components of the dielectric function display negative values across particular energy ranges, a characteristic that holds significant promise for potential applications in nanotechnology communications, offering minimal energy loss.

Probing the physical properties of Sr3AsX3 (X = F and Br) perovskite compounds for prospective solar cell applications employing the DFT framework

Here we have explored the structural, electronic, elastic and optical properties of halides perovskites Sr3AsX3 (X = F, Br) using the Vienna ab initio simulation package (VASP). The structural properties reveals that both compounds possess cubic phases with space group pm3m 221. The negative formation energy indicates the stability and synthetization of these materials. The electronic properties illustrate that both materials have a semiconducting nature. The band gap obtained through HSE is 2.5 eV and 2.23 eV for Sr3AsF3 and Sr3AsBr3 respectively. The mechanical stability is conformed from the obtained elastic constants; we further find that these materials have a brittle and anisotropic nature. The optical properties are explored in the energy range of 0 eV to 25 eV. The study of optical properties highlights that these materials have high absorption in energy range 2 eV to 10 eV. This work demonstrates that these halide perovskites have a lot of potential to prove themselves as the best candidates for solar cells.

The effect of f-electrons on the structural phase transition, mechanical and electronic properties in light rare-earth bismuthides

ABSTRACT The electronic structure, phase transition pressure and mechanical properties of light rare-earth bismuthides (PrBi, NdBi, PmBi and SmBi) have been investigated by full geometry optimization using Vienna Ab-Initio Simulation Package (VASP) which has been used in combination with the projector augmented wave (PAW) method and the generalized gradient approximation (GGA) over the local density approximation (LDA) for exchange-correlation functional. We focus our attention on the lattice constants and elastic constants of these compounds. These compounds undergo a phase transition from the NaCl (B1) structure to the body-centered tetragonal (BCT) structure. We also report the density of states (DOS) of these rare earth bismuthides. In the case of PrBi and NdBi, the 4f states are treated as valence states. The effects of on-site Coulomb repulsion and the spin-orbit coupling (SOC) on the electronic structure are also studied.

Continuous modulation of VO2 film’s phase transition threshold and transmittance via n-AZO/n-VO2 heterojunction

To solve the irreconcilable contradiction between the phase transition threshold and the optical property of VO2 film, an n-AZO/n-VO2 heterojunction, in which AZO is Al-doped ZnO, was constructed with the radio frequency (RF) magnetron sputtering and the post annealing. The effects of annealing on the composition and properties of vanadium oxide films have been investigated, as well as the effects of annealing and AZO layer thickness on the phase transition performance of the n-AZO/n-VO2 heterojunction. The results indicate that the V2O5 film will gradually transform into VO2 (M) through V6O13 and VO2 (B) during the reduction annealing at 500 °C. The phase transition temperature (Tc) of VO2 (M) film increases with the annealing temperature. In the heterojunction formed by the ohmic contact between AZO and VO2 layers, the free electrons will be injected into the VO2 layer from AZO layer, which reduces the heterojunction’s Tc from 69.2 to 41.5 °C. The first-principles calculations were performed with the Vienna Ab initio Simulation Package (VASP) to assist in the influence mechanism explanation. In addition to modulating Tc, the AZO layer in the heterojunction also plays an antireflection role, increasing the maximum visible transmittance of VO2 film by ∼ 10 %.

First principles molecular dynamics simulation and thermal decomposition kinetics study of CL-20.

2,4,6,8,10, 12-hexanitro-2,4,6,8,10, 12-hexazepane (CL-20) is a new energetic material with high performance and low sensitivity. In-depth study of the thermal decomposition mechanism of CL-20 is a necessary condition to improve its performance, ensure its safety, and optimize its application. On the basis of a large number of empirical force fields used in molecular dynamics simulation in the past, the machine learning augmented first-principles molecular dynamics method was used for the first time to simulate the thermal decomposition reaction of CL-20 at 2200 K, 2500 K, 2800 K, and 3000 K isothermal temperature. The main stable resulting compounds are N2, CO2, CO, H2O, andH2, where CO2 and H2O continue to decompose at higher temperatures. The initial decomposition pathways are denitration by N-N fracture, ring-opening by C-N bond fracture, and redox reaction involving NO2 and CL-20. After ring opening, two main compounds, fused tricyclic pyrazine and azadicyclic, were formed, which were decomposed continuously to form monocyclic pyrazine and pyrazole ring structures. The most common fragments formed during decomposition are those containing two, three, four, and six carbons. The formation rule and quantity of main small molecule intermediates and resulting stable products under different simulated temperatures were analyzed. Based on ab initio Bayesian active learning algorithm, efficient and accurate prediction of CL-20 is made using the dynamic machine learning function of Vienna Ab-Initio Simulation Package (VASP), which constructs the energy potential surface by learning a large number of data based on AIMD calculations. The result is a machine learning force field (MLFF). Then the molecular dynamics of CL-20 was simulated using the trained MLFF model. PAW pseudopotentials and generalized gradient approximation (GGA), namely, Perdew-Burke-Ernzerhof (PBE) functional, are used in the calculation. The plane wave truncation energy (ENCUT) is set to 550 eV, and using the Gaussian broadening, the thermal broadening size of the single-electron orbital is 0.05 eV. A van der Waals revision of the system with Grimme Version 3. The energy convergence accuracy (EDIFF) of electron self-consistent iteration is set to 1E-5 eV and 1E-6 eV, respectively. The two-step structure optimization is carried out using 1'1'1 k point grid and conjugate gradient method. The ENCUT was changed to 500 eV and EDIFF to 1E-5 eV, and NVT integration (ISIF = 2) of Langevin thermostat was used for machine learning force field training and AIMD simulation of the system.

First-Principles study on Li-ion migration properties in Li<sub>1+<i>x</i></sub> Al<sub><i>x</i></sub>Ti<sub>2-<i>x</i></sub>(PO<sub>4</sub>)<sub>3</sub> (LATP)

NASICON type materials are specific skeleton structures in which ions move in three dimensions. Li<sub>1+<i>x</i></sub>Al<sub><i>x</i></sub>Ti<sub>2-<i>x</i></sub>(PO<sub>4</sub>)<sub>3</sub> (LATP) is a promising NASICON type solid-state electrolyte for Li-ion batteries, due to its relatively high Li-ion conductivity, chemical stability to air and moisture and mechanical strength. Motivated by this, we studied the doping and electronic properties of Li<sub>1+<i>x</i></sub>Al<sub><i>x</i></sub>Ti<sub>2-<i>x</i></sub>(PO<sub>4</sub>)<sub>3</sub> (<i>x</i> = 0.00、0.16、0.33、0.50) and the transport properties of Li<sup>+</sup> in them using first-principles calculations based on density functional theory as implemented in Vienna ab initio Simulation Package (VASP). The results indicate that Al can substitute Ti to form stable structures. When the Al doping concentration is <i>x</i> = 0.16, the average bond length of Li-O bonds is the longest and the bonding strength is the weakest, This may lead to the expansion of channels for Li<sup>+</sup> migration, which facilitates the diffusion of Li<sup>+</sup>. With the increase of Al doping concentration, the strength of Ti-O bond remains almost unchanged. The electronic structure calculations exhibit that with the increase of Al doping concentration, the bandgap of LATP does not change much, and LATP all shows semiconductor characteristics. The differential charge results indicate that more electrons are localized on O-atoms surrounding the Al-dopant, causing the AlO<sub>6</sub> groups to form polarization centers. The study on the migration properties of Li<sup>+</sup> indicates that Li<sup>+</sup> exhibits different migration characteristics when it adopts one of three different migration modes (vacancy migration, interstitial migration and cooperative migration) : With the increase of Al doping concentration, the migration barriers of Li<sup>+</sup> increase in migration via vacancies involving only lattice site migration, And the migration barrier for LATP-0.16 is the lowest (0.369 eV). While in interstitial migration involving only interstitial sites, the migration barrier of Li<sup>+</sup> decreases accordingly. When the Al doping concentration is x=0.50, the migration barrier is the lowest (0.342 eV). In terms of cooperative migration, this migration mode involves both vacancy and interstitial sites, so the migration barrier first decreases and then increases with the increase of Al doping concentration. Thus, our study suggests that by varying the concentration of Al doping, the interstitial Li<sup>+</sup>content, migration channel structure, and the migration performance of Li<sup>+</sup> can be changed favorably. Our results provide a theoretical basis for improving the ion conductivity of Li in LATP with varying Al doping concentration in experiments.

The Mott transition in the 5d[formula omitted] compound Ba[formula omitted]NaOsO[formula omitted]: A DFT+DMFT study with PAW spinor projectors

Spin–orbit coupling has been reported to be responsible for the insulating nature of the 5d1 osmate double perovskite Ba2NaOsO6 (BNOO). However, whether spin–orbit coupling indeed drives the metal-to-insulator transition (MIT) in this compound is an open question. In this work we investigate the impact of relativistic effects on the electronic properties of BNOO via density functional theory plus dynamical mean-field theory calculations in the paramagnetic regime, where the insulating phase is experimentally observed. The correlated subspace is modeled with spinor projectors of the projector augmented wave method (PAW) employed in the Vienna Ab Initio Simulation Package (VASP), suitably interfaced with the TRIQS package. The inclusion of PAW spinor projectors in TRIQS enables the treatment of spin–orbit coupling effects fully ab-initio within the dynamical mean-field theory framework. In the present work, we show that spin–orbit coupling, although assisting the MIT in BNOO, is not the main driving force for its gapped spectra, placing this material in the Mott insulator regime. Relativistic effects primarily impact the correlated states’ character, excitations, and magnetic ground-state properties.

First-principles investigation of the catalytic mechanism of CeO2/KB composite separator in Li-S batteries

The CeO2/Ketjen Black (KB) composite separator has been shown to effectively reduce the shuttle effect and improve the reaction kinetics of lithium polysulfides (LiPSs) in lithium-sulfur (Li-S) batteries. A thorough investigation has been conducted using the Perdew-Burke-Ernzehof plus Hubbard U (PBE + U) calculations implemented within the Vienna ab initio simulation package (VASP). The focus has been on the catalytic mechanism of the separator, particularly the migration behavior of LiPSs and the conversion mechanism of Li2S2 → Li2S on CeO2 and KB surfaces. The study revealed that LiPSs have a strong preference for the CeO2 surface due to more potent adsorption energies. Moreover, it has been discovered that the subsequent migration and conversion processes of LiPSs are governed by the synergistic catalytic effect between CeO2 and KB. The rate-determining step in the overall catalytic process is the migration of Li2S2 on CeO2. These findings provide a deeper understanding of the catalytic mechanism and migration behavior of LiPSs, potentially guiding the development of advanced composite materials for Li-S batteries and facilitating the use of rare earth metal oxides for high energy storage and extended battery life.

Investigation of Stable Structures and Electronic States of Spinel MgCo2−ZNi0.5MnAlzO4 (z = 0, 0.3) during Discharge Process As Cathode Materials for Magnesium Rechargeable Batteries Using First-Principles Calculations

Introduction Recently, it is focused on storage batteries materials for reduce of greenhouse gases. In particular, the development of large equipment like as electric vehicles is driving demand for storage battery materials. Although lithium-ion batteries are currently used as storage battery devices, Li metal is a rare metal and expensive, and the development of higher capacity battery materials is needed. Our research group is focusing on magnesium secondary battery cathode materials. In previous report, spinel MgCo2-xMnxO4 (x=0~0.5) (space group Fd-3m) has synthesized and evaluated its battery characteristics, showing an initial discharge capacity of more than 200mAh/g when the Mn substitution amount is x=0.5.1) Since the inclusion of substituted species improves battery properties, we synthesized Al substituted spinel MgCo2-zNi0.5MnAlzO4. In this study, we reported that Mg/Co cation mixing, which was particularly problematic at z=0.3 was reduced compared to MgCo2-xMnxO4 resulting in improved cycle properties.2) The purpose of this study is to clarify the stable local structure of pristine and discharge process of spinel type MgCo2-zNi0.5MnAlzO4 (z=0, 0.3) and to determine the contribution of Al substitution to the electronic structure by performing electron density calculation. Calculation The structural relaxation calculation was performed by generalized gradient approximation (GGA) exchange-correlation potential used with a plane-wave cutoff energy of 550 eV, and 1×2×2 k-point mesh was applied, corresponding to the inverses of the lattice constants on Vienna Ab-initio Simulation Package (VASP) code. The convergence criterion for structural optimization was that the energy difference per iteration be less than or equal to 0.02 eV/Å. 2×1×1 supercell was created and structural relaxation calculation was performed on various initial structural models to determine the energetically optimal structure. Initial structure models were constructed to ensure reproduction of the occupancies determined by an average structure analysis from Rietveld analysis using synchrotron X-ray diffraction. Result and discussion In this study, we performed structural relaxation calculations for spinel-type MgCo2-zNi0.5MnAlzO4 (z=0, 0.3) to obtain the stable structure before and during charge-discharge. The initial model before charging and discharging was created based on the occupancy of each site obtained by crystal structure analysis using neutron diffraction measurements.2) The initial model at discharge was obtained by inserting Mg into the 16c vacancy site in the stable structure before charging and discharging. Figure 1 shows the stable structure after structural relaxation calculations before for a-1) z=0 and b-1) z=0.3 and after discharge (y=0.375) for a-2) z=0 and b-2) z=0.3, respectively. The solid circled Mg is the inserted one, and the dotted circle is the 8a site that became vacant after the structural relaxation calculation in Fig. 1. The crystal structure in pristine was spinel structure, however, it is found that the 4-coordinated 8a site became a vacancy and Mg occupied the 16c site, changing the crystal structure to a rocksalt structure after discharge. Since the 8a and 16c site are close to each other, the insertion of Mg into the 16c site causes a structural change due to the repulsion between atoms and cations on the 8a site, which leads to a chain transfer to other vacancy 16c sites. In particular, models with large structural changes tended to have stable structures. It is also found that Mg remained at the 8a site in z=0.3 shown in b-2) than in z=0 shown in a-2), and that Co at the 8a site could not move to the vacancy in z=0, and that the amount of change in the entire structure is less than that in z=0.3. As a result of partial density of states (PDOS) calculation, it is confirmed that Co and Mn had 2.6 ~ 2 valence and Mn is considerably close to 3 valence during discharge. It is also found that the PDOS of Ni did not almost change before and after discharging, and that no valence change occurred. These results are consistent with those of previously reported XANES measurements.2) Therefore, the model in Fig. 1 determined in this study is considered to be valid. Acknowledgement This research was financially supported by JST, ALCA-SPRING Grant Number JPMJAC1301, Japan. This work was also supported in part by JSPS KAKENHI Grant Number 20K15382, Japan. Dr. Koji Ohara of JASRI (Japan Synchrotron Radiation Research Institute for assistance with synchrotron X-ray total scattering measurements (BL04B2, SPring-8, Proposal Nos. 2019B1249).1) Y. Idemoto, M. Ichiyama et al., J. Power Sources, 482 , 228920 1-9 (2021)2) Y. Hirata, Y. Idemoto et al., ECS Meeting s, MA2020-02 , 3451 (2020) Figure 1

An implicit electrolyte model for plane wave density functional theory exhibiting nonlinear response and a nonlocal cavity definition.

We have developed and implemented an implicit electrolyte model in the Vienna Ab initio Simulation Package (VASP) that includes nonlinear dielectric and ionic responses as well as a nonlocal definition of the cavities defining the spatial regions where these responses can occur. The implementation into the existing VASPsol code is numerically efficient and exhibits robust convergence, requiring computational effort only slightly higher than the original linear polarizable continuum model. The nonlinear + nonlocal model is able to reproduce the characteristic "double hump" shape observed experimentally for the differential capacitance of an electrified metal interface while preventing "leakage" of the electrolyte into regions of space too small to contain a single water molecule or solvated ion. The model also gives a reasonable prediction of molecular solvation free energies as well as the self-ionization free energy of water and the absolute electron chemical potential of the standard hydrogen electrode. All of this, combined with the additional ability to run constant potential density functional theory calculations, should enable the routine computation of activation barriers for electrocatalytic processes.