Simulation Package Research Articles

Density functional theory study of hydrogen and oxygen reactions on NiO(100) and Ce doped NiO(100).

This study aims to reveal the reaction mechanisms of H2 and O2 on the NiO(100) and Ce-doped NiO(100) surfaces using the density functional theory (DFT) combined with the on-site Coulomb correction (DFT + U) method. It was found that H2 and O2 react favorably on the reduced surfaces of both materials. However, after the oxygen vacancy is filled, the activation energy for the reaction between H₂ and lattice oxygen increases. Ce doping reduces this activation energy to 1.64eV (compared to 3.16eV for pure NiO(100)). The enhanced activity of lattice oxygen due to Ce doping is attributed to the charge transfer in the Ce-O bond, which leads to the electronic localization around O atoms and weakens the activation energy barrier. Moreover, the presence of Ce facilitates the formation of a sub-stable OH intermediate on the reduced surface, ensuring the sustainability of the reaction. This study provides a theoretical basis for the design of high-performance nickel-based hydrogen deoxidizers and contributes to promoting the research and development process of nickel-based catalysts in related fields. The calculations were performed using the Vienna ab initio simulation package (VASP) module of the MedeA® software. The exchange-correlation energy calculations are performed using the Perdew, Burke and Ernzerhof (PBE) functional within the generalized gradient approximation (GGA). The transition states were calculated using the MedeA® Transition State Search Module, based on the climbing-image nudged elastic band (CI-NEB) method.

High-performance, self-powered ZnO NWs-ZnSe heterojunction photodetectors for superior visible and near-infrared detection

Abstract We present the development of a type-II heterojunction photodetector (PD) comprising Ag/ZnO nanowires (NWs)/ZnSe/In, fabricated on a commercially available Si substrate. ZnO NWs were hydrothermally synthesized on thermally evaporated ZnSe thin films, with scanning electron microscopy (SEM) analysis revealing uniform, vertically aligned ZnO NWs on the ZnSe layer. Cross-sectional SEM imaging determined the thickness of the In/ZnSe thin film to be approximately 460 nm, with ZnO NWs exhibiting an average diameter of ∼161 nm. Structural analysis of the ZnSe thin film, annealed at 370 °C in an ambient environment, identified a prominent ZnSe peak at 27.48° alongside peaks at 30.98° and 33.21° corresponding to In2O3 and ZnSeO3, respectively. The ZnO NWs, under similar annealing conditions, displayed a strong (002) peak, confirming vertical growth. Hall effect measurements revealed a transition from p-type carriers in as-deposited ZnSe thin films to n-type in the annealed ZnSe and ZnO NWs, attributed to the formation of In2O3 as evidenced by XRD. The PD exhibited the highest photoresponse under IR illumination (950 nm), surpassing responses to green (515 nm) and blue (456 nm) LEDs, with a short-circuit current (I sc) of −26 μA and an open-circuit voltage (V oc) of +80 mV, characteristic of a self-powered device. In contrast, minimal photoresponse was observed in a Schottky-type Ag/ZnSe/In junction on the Si substrate. The photoresponse mechanism was elucidated using an energy band diagram, while density functional theory simulations using Vienna ab initio simulation package provided a strong correlation with the experimental data, validating the structural and electronic properties of the heterojunction.

The optoelectronic properties of boron nitride nanotubes of armchair (7, 7) and zigzag (12, 0) types: A theoretical study

In this article, the electronic and optical properties of single-walled boron nitride nanotubes (SWBNNTs) in zigzag (12, 0) and armchair (7, 7) configurations were examined using density functional theory (DFT) with the Vienna Ab initio Simulation Package (VASP). The analysis shows that SWBNNTs exhibit electronic characteristics with a density of states and an electronic band gap around 4 eV. Regarding optical properties, the calculations reveal key features such as absorption, reflection, and dielectric constant, with a notably strong absorption peak in the ultraviolet region. These results highlight the potential of SWBNNTs for applications in optoelectronic devices.

Structural, electronic, mechanical, optical and magnetic properties of RhNbZ (Z = Li, Si, As) Half-Heusler compounds: a first-principles study

Abstract Structural, mechanical, electronic, optical and magnetic properties of the cubic RhNbZ (Z = Li, Si, As) half-Heusler compounds is reported using density functional theory (DFT) as implemented in quantum espresso simulation package. Structurally, the compounds are most stable when they are in type I atomic arrangement. Studies of mechanical properties indicate that all the three compounds are ductile in nature and mechanically stable. Calculations of electronic band structure and density of states (DOS) affirm that RhNbSi is a semi-conductor with an indirect band gap of 0.662 eV and 1.0095 eV from generalized gradient approximation (GGA) and GGA+U approaches respectively, where U is Hubbard parameter, RhNbLi has metallic property under both GGA and GGA+U approaches whereas RhNbAs has metallic nature under GGA prediction but it has half-metallic property under GGA+U approach, a property which is essential for spintronic applications. Optical parameters such as dielectric function, reflectivity, refractive index, extinction coefficient, absorption coefficient, optical conductivity and electron energy loss were estimated in the photon energy range of 0–40 eV. Results from these properties calculations reveal that both absorption coefficient and optical conductivity have maximum values whereas electron energy loss has minimum value in the lower energy ranges which show that the materials under our study can be considered as potential candidates for optoelectronic applications. From magnetic property calculations, RhNbSi is predicted to be nonmagnetic material but RhNbLi and RhNbAs have magnetic nature.

CO- and H2S-adsorbed one-dimensional AlSi structures for gas sensing applications.

The potential applications of low-dimensional materials continue to inspire significant interest among researchers worldwide. This study investigates the properties of one-dimensional AlSi monolayers, specifically AlSi nanoribbons, and their adsorption behaviour with CO and H2S molecules. The electronic, magnetic and optical properties of these systems are calculated using density functional theory and the Vienna Ab initio Simulation Package. Results indicate that the structures remain relatively planar with negligible buckling heights. All three studied structures exhibit non-zero magnetic moments; notably, CO adsorption enhances the magnetic moment of the pristine AlSi nanoribbon, whereas H2S adsorption reduces it. Adsorption energy calculations reveal that CO exhibits stronger adsorption compared to H2S. Furthermore, a detailed investigation of the optical properties-including the real and imaginary parts of the dielectric function, absorption coefficient and electron-hole density-demonstrates the potential of these structures in nanotechnology applications, particularly for CO and H2S gas sensing.

Density functional theory study of Mg–Ho intermetallic phases

Abstract The present study explores the structural, phase stability, mechanical, and electrical properties of Mg–Ho intermetallic phases, namely Mg24Ho5, Mg2Ho, and MgHo. The investigation is conducted using the first-principles plane-wave pseudopotential method within the framework of density functional theory, as implemented in the Vienna Ab initio Simulation Package. The primary objective of this research is to illuminate the phase stability and mechanical behavior of these compounds, which are of paramount importance for their potential applications in magnesium alloys. The study determines the formation enthalpy (ΔH) and elastic constants (C ij ) for each intermetallic phase and calculates the elastic moduli of the corresponding polycrystalline materials. The findings of this study reveal that the MgHo phase exhibits the highest absolute value of formation enthalpy (ΔH = −8.01 kJ·mol−1), indicating its superior stability among the three investigated intermetallic phases. As the concentration of Ho in Mg increases, the G/B ratio for the phases decreases from 1.02 to 0.60 (>0.57), suggesting that the intermetallic phases are stable, albeit brittle. The elastic anisotropy index (A U), derived from the elastic constants (C ij ), follows an ascending order of Mg24Ho5, Mg2Ho, and MgHo, signifying that MgHo possesses the most favorable elastic anisotropy among the studied phases.

Comparison of essential physical properties between pristine armchair silicene nanoribbons and those doped with Ge and As

In this paper, some physical properties of pristine armchair silicene nanoribbons (ASiNR) and those doped with Ge (ASiGeNR) and As (ASiAsNR) using the VASP (Vienna ab initio simulation package) computational program, by using density functional theory. The results show significant differences in the structural and electronic properties between these systems. For ASiGeNR and ASiAsNR, structural parameters such as the distance between two nearest-neighbor atoms in the hexagonal ring, the distance between two farthest atoms, and the buckling height are all larger compared to ASiNR. While ASiNR and ASiGeNR have band gaps of approximately 0.262 eV and 0.2410 eV, respectively, opening at the Γ point, ASiAsNR does not have a band gap. The results indicate that ASiNR and ASiGeNR exhibit semiconductor properties, while ASiAsNR exhibits metallic properties. For ASiGeNR, the substitution of Ge leads to a reduction in bandgap and an increase in thermal conductivity, attributed to the energy level of Ge being close to that of Si. For ASiAsNR, the substitution with As increases the density of states at the top of the valence band, suggesting better electrical conductivity. ASiNR, with its wide bandgap, is suitable for applications in semiconductor devices such as MOSFETs and sensors. ASiGeNR is well-suited for optoelectronic applications such as solar cells or light-emitting diodes (LEDs), while ASiAsNR is appropriate for spintronics or high-speed electronic devices.

Characterization of intrinsic radiation in LYSO scintillators using GEANT4 and SimSiPM simulations.

The intrinsic radiation spectra of LYSO scintillators are investigated through detailed GEANT4 and SimSiPM simulations, focusing on how changes in configuration and size influence the radiation characteristics. Using these simulation packages together, a comprehensive simulation of the physical processes as well as a detailed simulation of the photodetector response, including factors such as dark count rate, optical crosstalk, afterpulse, noise, and saturation effects, was performed. The results of the simulations indicate that the primary factor affecting the intrinsic radiation pattern is the total volume of the crystal, rather than surface treatments or minor geometric variations. The consistency between GEANT4 and SimSiPM simulations confirms the validity of using these simulation methods to analyze the spectral behavior of LYSO scintillators detailed in various applications such as positron emission tomography and nuclear spectroscopy.

An Efficient Clustered N-Tier Computing Scheme for Large-Scale IoT-Enabled Healthcare Environments

Recently, Internet of Things (IoT) technology has become popular and applicable in different fields. The exchangeable data through IoT systems are extremely huge. This poses a great challenge in constructing a scalable and reliable computing scheme for IoT environments. Therefore, an efficient computing scheme for an IoT-enabled healthcare environment was proposed in this paper. The computing scheme idea was based on the use of cloud, fog, mist and edge computing strategies after dividing their resources into N-tiers. For easy management, these tiers were clustered depending on their geographical distribution. The number of tiers for each computing strategy dynamically changed depending on the computing load. Each tier had its own capabilities. Therefore, selecting a computing strategy and its tier was achieved regarding the data requirements and the specs of each computing resource. To evaluate the proposed computing scheme, a network simulator package (NS-3) was used to construct a simulation for the IoT-enabled healthcare environment and the computing scheme. Most simulation results of our computing scheme were compared with the cloud/fog/mist, cloud/fog and cloud computing schemes. Finally, the simulation results proved that the proposed computing scheme outperformed the performance of other traditional computing schemes regarding the following performance metrics: Delay, utilization, energy consumption, beneficial users and different healthcare organization complexities.

Impact of nuclear fragmentation on the stopping power ratio of12C ion beams.

Nuclear fragmentation generates a diverse dosimetric environment in the path of 12C ion beams. Concise parametrization of the beam's composition is paramount for determining key correction factors in clinical dosimetry. This study sets out to provide such a parametrization based on detailed Monte Carlo simulations of clinically relevant 12C beams. Special attention was paid to the products of nuclear fragmentations and their importance in determining the stopping power ratios. Using the Monte Carlo simulation package GATE, the spectral fluence of all primary and secondary particles in water were computed at different depths for selected clinically relevant incident energies. Collision-stopping power data was taken from the ICRU90, SRIM and MSTAR database, as well as from previous publications. The choice of stopping power data was shown to have a bigger impact on the resulting stopping power ratio than the choice of physics lists for the simulations. A comprehensive analysis of the relationship between fragmentation and dosimetric data has been provided. This study compared different methods for determining spectral fluence-based stopping power ratios, which is essential for accurate ion beam dosimetry.

MRSimulator: A cross-platform, object-oriented software package for rapid solid-state NMR spectral simulation and analysis.

The open-source Python package, MRSimulator, is presented as a simple-to-use, fast, versatile, and extendable package capable of simulating one- and higher-dimensional Nuclear Magnetic Resonance (NMR) spectra under static, magic-angle, and variable-angle conditions. High benchmarks in spectral simulations are achieved by assuming that there are no degeneracies in the energy eigenstates, i.e., all dipolar couplings are in the weak limit and that there are no rotational resonances during evolution periods. Under these assumptions, the symmetry pathway formalism is exploited to reduce an NMR method applied to a spin system into a sum of individual transition pathways, whose signals are more efficiently calculated individually than as part of a full-density matrix simulation. To increase numerical efficiencies further, our approach restricts coherence transfer among transitions to pure rotations about an axis in the x-y plane of the rotating frame or through an artificial total mixing operation between selected transitions of adjacent free evolution periods. The assumptions used in this approach are valid for most commonly used solid-state NMR methods. Details of the implementation, along with example code usage, are given, including a least-squares spectral analysis.

PRIM-AES Software Package for Simulation of Transient Modes at Power Units with VVER Reactors

PRIM-AES Software Package for Simulation of Transient Modes at Power Units with VVER Reactors

Investigation of the Physical Attributes of Sr2GeCrO6, Sr2MgMoO6, Ba2MgMoO6, Ba2ZnMoO6, and Ba2HgWO6 Double Perovskite Oxides

A density functional theory‐based study on the physical properties of significant double perovskite oxides Sr2GeCrO6, Sr2MgMoO6, Ba2MgMoO6, Ba2ZnMoO6, and Ba2HgWO6 has been conducted using the Vienna Ab initio Simulation Package and WIEN2K code. Structural analysis reveals the simple cubic crystal structure of double perovskite oxides. Phonon properties indicate the dynamical stability of Sr2GeCrO6, Ba2MgMoO6, and Ba2ZnMoO6 compounds. The band structure analysis indicates the metallic character of Sr2GeCrO6. However, generalized gradient approximation of Perdew–Burke–Ernzerhof and modified Becke–Johnson both suggest the indirect semiconducting nature of Ba2MgMoO6 and Ba2ZnMoO6. The crystal orbital Hamilton population (–COHP) examination evidences the strongest bonding interactions of O–Ba in these perovskite oxides. Both Ba2MgMoO6 and Ba2ZnMoO6 compounds exhibit p‐type character, as indicated by the partial charge density distributions in the highest occupied molecular orbital and lowest unoccupied molecular orbital (LUMO) orbitals, which govern the band edges near Fermi level. LUMO orbitals are located on Mo and O atoms and are composed of heteronuclear s‐ and p‐type interactions. The investigation comprehensively analyzes calculated optoelectronic properties, including complex dielectric function, optical conductivity, loss function, refractive index, and so on. These parameters are examined in detail, offering profound insights into the materials’ optical and electronic characteristics.

Layer-dependent electronic and magnetic properties of SrMnO3/LaAlO3 superlattices

In this paper, we investigated the structural, electronic, and magnetic properties of SrMnO3/LaAlO3 (SMO/LAO) (001) heterostructures using density functional theory (DFT) with the Hubbard U correction, employing the Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation within the Vienna Ab Initio Simulation Package (VASP). Three distinct superlattices—SMO1.5/LAO1.5, SMO1.5/LAO2, and SMO2.5/LAO1—were analyzed by varying the layer thicknesses to tailor their properties. The SMO1.5/LAO1.5 and SMO2.5/LAO1 superlattices exhibit antiferromagnetic (AFM) ground states, while the SMO1.5/LAO2 superlattice shows a ferromagnetic (FM) ground state. Electronic structure analysis reveals that SMO1.5/LAO1.5 and SMO1.5/LAO2 are metallic, whereas SMO2.5/LAO1 exhibits half-metallic behavior. By strategically controlling the layers in SMO/LAO heterostructures, it is promising to engineer electronic and magnetic properties that are important for developing advanced magnetic and nano-electronic devices.

Benchmarking quantum computer simulation software packages: State vector simulators

Rapid advances in quantum computing technology lead to an increasing need for software simulators that enable both algorithm design and the validation of results obtained from quantum hardware. This includes calculations that aim at probing regimes of quantum advantage, where a quantum computer outperforms a classical computer in the same task. High performance computing (HPC) platforms play a crucial role as today’s quantum devices already reach beyond the limits of what powerful workstations can model, but a systematic evaluation of the individual performance of the many offered simulation packages is lacking so far. In this Technical Review, we benchmark several software packages capable of simulating quantum dynamics with a special focus on HPC capabilities. We develop a containerized toolchain for benchmarking a large set of simulation packages on a local HPC cluster using different parallelisation capabilities, and compare the performance and system size-scaling for three paradigmatic quantum computing tasks. Our results can help finding the right package for a given simulation task and lay the foundation for a systematic community effort to benchmark and validate upcoming versions of existing and also newly developed simulation packages.

Development of Novel Ternary Alloy of CSiSn for Low-Cost Next Generation Photovoltaics

Multijunction solar cells exhibit enhanced efficiencies by harnessing the energy of various segments of the solar spectrum. Presently, the most efficient cell on the market comprises three layers of InGaP/InGaAs/Ge, denoted as blue, green, and red cells based on their energy absorption levels [1]. However, increasing the number of layers to enhance efficiency escalates production costs. The high costs are mainly due to the availability of the elements and their limited abundance of III-V alloys. To mitigate these expenses associated with multijunction solar cells, it is imperative to develop these cells with a material compatible with silicon substrates, thus facilitating industrial scalability. The best choices of materials are group IV alloys such as C, Si, and Sn. However, achieving this goal necessitates the development of a direct wide bandgap Group IV alloy that seamlessly matches with the silicon lattice. Recent research suggests that alloying Ge and Sn results in a true direct bandgap alloy and incorporating Si into GeSn enables engineering the bandgap and lattice constant [2]. However, this approach lacks sufficient coverage of the blue and green spectrum due to limited bandgap adjustments and a mismatch in lattice size with Si. Introducing a new group IV ternary alloy that resolves this issue by enabling lattice-matched growth to silicon, ensuring full spectrum coverage and compatibility with silicon substrates is the key to revolutionize this industry.The C-Si-Sn (CST) alloy is the unique answer to this problem, however, developing group IV alloys does not follow the same path for all elements as the lattice size and crystal structures vary from one to another. Diamond cubic crystal structure is shared between the three elements but it is not a universally stable crystal under all conditions; carbon tends to form diamond structures under high temperature and pressure, whereas tin's stability is limited to temperatures below 13°C. However, recent advancements in alloy growth under non-equilibrium conditions showed successful incorporation of Sn in Ge exceeding thermal equilibrium limits up to 25%. Also, our team reported the growth of Sn incorporation in Si as high as 3% using plasma-enhanced chemical vapor deposition at 300°C. Moreover, we have reported on low-temperature diamond deposition and silicon growth at 250°C [3]. Therefore, the path to grow ternary CST alloys is feasible.In this paper we present the bandgap predictions of CST alloy and its stability using density functional theroy as well as the growth pathways that allow deposition of the alloy using ultra-high vacuum plasma enhanced chemical vapor deposition (UHV-PECVD).The electronic band structure of CST alloys relies significantly on band bowing, necessitating adjustments in compositions to attain a direct bandgap. Moreover, CST alloys don't achieve full miscibility among constituents, requiring simulation via Density Functional Theory (DFT) to forecast the electronic band gap of both binary alloys of C-Si-Sn and the ternary alloy of CST. DFT calculations were done using generalized gradient approximation- Perdew–Burke–Ernzerhof (GGA-PBE) with Vienna Ab-initio Simulation Package (VASP). The simulations show that a balance between C and Sn is needed to make the crystal stable.The band structure of CST is estimated using Vegard’s law with proposed bowing parameters reported in an earlier publication [4]. This relationship is shown below:Upon examination of the direct transitions observed in CSn and Si, it is anticipated that the ternary alloy of CST would exhibit a direct bandgap transition region. The vertices of this triangular configuration represent the maximum bandgap at 2.48 eV for C0.55Sn0.45, the minimum bandgap for Sn at -0.41 eV, and the third point at 0.539 eV for Si0.50Sn0.50.Considering the DFT simulation results for both bandgap and crystal stability of CST, the growth pathways were designed. Growth was achieved utilizing commercially available precursors: CH4 for carbon, SiH4 for silicon, SnCl4 for tin, and hydrogen (H2) as both the carrier and diluent gas. The growth process was facilitated by a capacitively coupled plasma system powered by a 13.56 MHz radio-frequency (RF) power supply.Raman spectroscopy (Fig.1)was employed to characterize the CST samples, to investigate the impact of flow ratio and plasma power on material quality and the incorporation of carbon and tin. The observation of the Si-C, Si-Sn, and C-Sn peaks, associated with the transverse optical (TO) and longitudinal optical (LO) modes for each bond. Moreover, the samples were investigated using in-depth Xray Photoelectron Spectroscopy that show uniform incorporation of the C-Si-Sn element. The results will be shown in the conference. Figure 1

Asparagus: A toolkit for autonomous, user-guided construction of machine-learned potential energy surfaces

With the establishment of machine learning (ML) techniques in the scientific community, the construction of ML potential energy surfaces (ML-PES) has become a standard process in physics and chemistry. So far, improvements in the construction of ML-PES models have been conducted independently, creating an initial hurdle for new users to overcome and complicating the reproducibility of results. Aiming to reduce the bar for the extensive use of ML-PES, we introduce Asparagus, a software package encompassing the different parts into one coherent implementation that allows an autonomous, user-guided construction of ML-PES models. Asparagus combines capabilities of initial data sampling with interfaces to ab initio calculation programs, ML model training, as well as model evaluation and its application within other codes such as ASE or CHARMM. The functionalities of the code are illustrated in different examples, including the dynamics of small molecules, the representation of reactive potentials in organometallic compounds, and atom diffusion on periodic surface structures. The modular framework of Asparagus is designed to allow simple implementations of further ML-related methods and models to provide constant user-friendly access to state-of-the-art ML techniques. Program summaryProgram Title:AsparagusCPC Library link to program files:https://doi.org/10.17632/9w9xw7mp2h.1Developer's repository link:https://github.com/MMunibas/AsparagusLicensing provisions: MITProgramming language: PythonSupplementary material: Access to Documentation at https://asparagus-bundle.readthedocs.ioNature of problem: Constructing machine-learning (ML) based potential energy surfaces (PESs) for atomistic simulations is a multi-step process that requires a broad knowledge in quantum chemistry, nuclear dynamics and programming. So far, efforts mainly focused on developing and improving ML model architectures. However, there was less effort spent on providing tools for consistent and reproducible workflows that support the construction of ML-PES for a variety of chemical systems for the broader science community.Solution method:Asparagus is a program package written in Python that provides a streamlined and extensible workflow with a user-friendly command structure to support the construction of ML-PESs. This is achieved by bundling and linking data generation and sampling techniques, data management, model training, testing and evaluation tools into one modular, comprehensive workflow including interfaces to other simulation packages for the application of the ML-PESs. By lowering the entrance barriers especially for new users, Asparagus supports the generation and adjustment of ML-PESs that allow an increased focus on the physico-chemical evaluation of the chemical system or application in molecular dynamics simulations.Additional comments including restrictions and unusual features:Asparagus is a modular package written in Python providing an underlying structure for further extensions and maintenance. Currently, methods based on message-passing neural network (NN) models using the PyTorch Python package are available. Additions of new models and interfaces to already implemented modules are possible. The NN architecture and hyperparameters are stored in a global configuration module and as a json file for documentation. Except for essential input information, default input parameters are used if not specifically defined otherwise, which allows a quick setup for the construction of a ML-PES but also the fine-tuning for specific needs.

Experimental Evaluation and Density Functional Theory Analysis of Activation Barriers in Dry Reforming Reaction Using Ni Nanoparticle-Supported CeO2 Novel Flower-like Catalyst

IntroductionIn the realm of renewable energy, biomass emerges as a crucial resource, capable of generating methane through anaerobic fermentation. This methane, in its role as a hydrogen carrier, presents an opportunity for fuel cells to leverage their high efficiency in electricity generation. Recent studies have illuminated the potential of biomass utilization, particularly in converting waste from shrimp farming into methane[1][2]. The prospect of utilizing revenue from shrimp farming to offset investments in fuel cells underscores the symbiotic relationship between these industries and drives interest in exploring new avenues for sustainable energy production.Efficient extraction of hydrogen from methane is an important factor in optimizing the fuel cell systems described above. Consequently, there has been a burgeoning focus on improving the efficiency of the dry reforming of methane (DRM) reaction. Within this context, CeO2 loaded with Ni nanoparticles has emerged as a promising catalyst, holding the potential to innovate methane utilization in fuel cells. This study embarks on a meticulous investigation into the dissociation reactions of methane and carbon dioxide, key steps in the DRM reaction, aiming to elucidate the underlying mechanisms and enhance reaction efficiency.MethodologyThe methodology employed in this study density functional theory (DFT) to calculate activation barriers for each dissociation reaction. Leveraging the plane-wave DFT method within the Vienna ab initio simulation package (VASP), the study explores diverse configurations of tetrahedral Ni nanoparticles on CeO2(111) surfaces. Through the nudged elastic band (NEB) method, activation barriers for methane and carbon dioxide dissociation were determined for each configuration. To validate these computational findings, experimental DRM reaction tests were conducted utilizing a Ni nanoparticle-supported flower-shaped CeO2 catalyst specifically synthesized for this study. Then, the activation barriers were calculated from the amount of hydrogen gas produced and methane consumed, offering a comprehensive understanding of reaction kinetics.Results and discussionResults from the study reveal intriguing insights into methane dissociation kinetics. The activation barrier for methane dissociation is found to range from 0.80 eV to 1.03 eV, depending on the loading site of Ni nanoparticles, closely mirroring the value derived from experimental methane consumption rates (=0.67 eV). On the other hand, the dissociation of carbon dioxide exhibits higher activation barriers compared to methane dissociation, suggesting its role as a rate-limiting step in the DRM reaction. Particularly noteworthy is the study's suggestion that augmenting the positive charge of Ni nanoparticles may enhance methane dissociation, offering a promising avenue for catalyst optimization in DRM processes.[1] Y. Shiratori et al., Biogas Power Generation with SOFC to Demonstrate Energy Circulation Suitable for Mekong Delta, Vietnam. Fuel Cells 19, 346-353 (2019).[2] P. H. Tu et al., Paper‐structured catalyst with a dispersion of ceria‐based oxide support for improving the performance of an SOFC fed with simulated biogas. Fuel Cells, 1-11 (2024).

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

Introduction In recent years, clean energy materials such as storage battery materials have been attracting attention in order to reduce greenhouse gas emissions. Li ion batteries (LIB) are already widely used as batteries for laptop and smartphones. However, Li metal is expensive and new storage battery materials with higher volumetric energy density are needed to be developed for application in large power supplies. Therefore, storage battery materials using Mg metal with divalent ions are currently attracting attention. Our group has been developing spinel Mg-(Co, Ni, Mn, Al)2-O4 cathode materials with three-dimensional diffusion pathways1). Spinel MgCo2-zNi0.5MnAlzO4 (z=0, 0.3) were synthesized and electrochemical tests revealed that the Al substituted material has particularly improved battery properties. Furthermore, the stable structure and electronic state of pristine MgCo2-zNi0.5MnAlzO4 (z=0, 0.3) were calculated using first principles calculations to clarify the effect of substituted species2). The results predicted that the Mg-O bonding around Al was specifically weakened, allowing Mg to diffuse easily move the crystal. In this study, we clarify the stable structure of spinel MgCo2-zNi0.5MnAlzO4 (z=0, 0.3) after discharge and charge, and clarify the electronic structure and the mechanism of Mg intercalation during charge and discharge processes. 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 for pristine model and during discharge and charge models 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. Result and discussion In this study, the stable structure of MgCo2-zNi0.5MnAlzO4 (z=0.3) during discharge was first obtained from the stable pristine structure. Figure 1 a) and b) show the stable structures of pristine and discharge model obtained by structural relaxation calculation, respectively. Fig. 1 b) is the stable structure after discharge in which Mg atoms are inserted into the vacancy 16c site in the stable pristine structure shown in a) (Mg insertion amount is 0.375). After insertion of Mg, the atoms on the 8a site move into the direction of the arrow in shown in b) to vacant 16c site, resulting in a vacancy at the 8a site. It is clear that the structural change from a spinel type structure to a rocksalt type structure partially occurs during the discharge.Therefore, we further show in Fig. 1 c) the stable structure of z=0.3 after charging in which the same amount of Mg insertion on the 16c site in the stable structure during discharge shown in b) is desorbed. After structural relaxation, Mg atoms on 16c site indicated by the dashed circle migrates to vacant 8a site during charge. During charging, it is apparent that the partial rock-salt type structure reverses to spinel type due to the desorption of Mg. The desorption of Mg from the 16c sites around the 8a vacancy site reduces the repulsion between cations, allowing the remaining 16c site Mg to move to the 8a site and return to the spinel type structure. Therefore, if a large structural change occurs during discharge, in which Mg insertion increases and almost all 8a site Mg becomes vacancies, it is not possible to return to the spinel type structure during charging. However, some 8a sites remain vacant in Fig. 1 c). When Co with cation mixing on the 8a site moves to the 16c site during discharge, Co cannot move to vacant 8a site because the bond between Co-O is much stronger than the bond between Mg-O. Therefore, it is clear that the Co influence at the 16c site also prevents the adjacent Mg from migrating to the 8a site, resulting in vacancies. Therefore, it is clear that due to the influence of Co at the 16c site, Mg adjacent to Co also cannot migrate to the 8a site. The cation mixing between Mg and transition metals is suppressed, and the change to a rocksalt type structure during discharge is suppressed during the charge-discharge process. Acknowledgement This research was financially supported by JST, GteX Program Grant Number JPMJGX23S1, Japan.1) Y. Hirata, Y. Idemoto et al., ECS Meeting s, MA2020-02 , 3451 (2020)2) C. Ishibashi, R. Takeuchi, N. Kitamura, Y. Idemoto, J. Phys. Chem. C., 127, 10470-10489 (2023). Figure 1

Design and performance evaluation of eco-friendly Ba(Zr0.95Ti0.05)S3/MASnI3 based perovskite solar cells utilize a variety of hole and electron transport materials

This research is a comprehensive analysis that provides a new model for perovskite solar cells (PSCs). Halide PSCs are the preferred option for solar absorbers in photovoltaic (PV) technology because it has superior optical properties, enhanced efficiency, lightweight nature, and significantly reduced cost. In this study, the simulation of the double-absorber layer organic–inorganic perovskite solar cells (PSC) has been carried out, where Ba(Zr0.95Ti0.05)S3 is used as the upper absorber layer, and MASnI3 is used as the lower absorber layers. It is examined using the solar cell research software SCAPS-1D simulation package. The main object of this research is to test the congenial components for the hole-transporting layers (HTL) and electron-transporting layers (ETL). In addition, this research goal is to ascertain better parameters for active layer thickness, temperature-absorbing defect density, and metal-work functions for the recommended PV cell performance. After optimizing the proposed solar cell structure by changing various components in ETL and HTL, the highest result attained the FTO/SnS2/Ba(Zr0.95Ti0.05)S3/MASnI3/CuO/Au structure, which exhibits an open circuit voltage of Vo = 1.2907 V, fill factor of 86.21 %, short-circuit current of Jsc = 34.7308 mA/cm2, and a maximum power conversion efficiency (PCE) of 38.65 %. The headway is attained by engaging SnS2 as the ETL and CuO as the HTL in the structure. Using the Scaps-1D simulation, we optimized temperature, thickness, defect density, shallow acceptor density, and back contact work functions. It was attained by leaving a thickness of 1 µm for the MASnI3 absorber and 0.01 µm for the Ba(Zr0.95Ti0.05)S3 absorber.