Search Results (329)

Helium accumulation is a major contributor to swelling, gas release, and mechanical degradation in oxide nuclear fuels under irradiation. This study employs first-principles density functional theory (DFT) to investigate helium behavior in thorium-based mixed oxide (MOX) fuels. A series of (Th_1−xPu_x)O₂ and (Th_1−xU_x)O₂ solid solutions (x = 0, 0.25, 0.5, 0.75, and 1) was constructed, and the corresponding ground-state configurations were determined through total-energy minimization. The effects of 4.167 at.% helium incorporation on structural stability, electronic structure, elastic response, and thermal expansion were evaluated. Helium migration in ThO₂, PuO₂, and UO₂ was further investigated at octahedral interstitial, metal-vacancy, and oxygen-vacancy sites. Positive helium incorporation energies indicated that helium incorporation is energetically unfavorable for all compositions. Vegard-like behavior was preserved for lattice constants and metal–oxygen bond lengths. The 2.06 eV band gap of UO₂ disappeared after helium incorporation, whereas band-gap variations in most MOX compositions remained below 0.7 eV. Helium reduced the bulk moduli of (Th_0.75U_0.25)O₂ and UO₂ by 3.75% and 7.94%, respectively. Thermal expansion coefficients followed the order α_L-UO2 > α_L-PuO2 > α_L-ThO2, with α_L of UO₂ nearly doubling. Metal vacancies acted as helium traps, whereas adjacent oxygen vacancies provided the lowest migration barrier of 0.42 eV. These results indicate that increasing ThO₂ content improves the resistance of MOX fuels to helium-induced degradation. Full article

Uranium nitride (UN) is considered a promising candidate material for advanced nuclear fuels in Generation IV reactors due to its high thermal conductivity and excellent fission product retention capability. However, the surface corrosion behavior of UN in oxygen-containing environments severely limits its practical application. In this work, first-principles calculations based on density functional theory (DFT) were employed to systematically investigate the adsorption and dissociation behaviors of O₂ molecules and O atoms on the UN(100), (110), and (111) surfaces. The electronic structure mechanisms underlying the adsorption were elucidated through analysis of surface work function, projected density of states (PDOS), Bader charge, and charge density difference. The calculated results show that O₂ molecules undergo thermodynamically highly favorable dissociative chemisorption on all three UN surfaces at 0 K, with the O–O bond length stretched to 1.44–1.50 Å, characteristic of a peroxo-like (O₂²⁻) species, which is intermediate between the superoxide (O₂⁻, ~1.33 Å) and complete dissociation. The most stable adsorption configurations on each surface are: (100)-H site (−4.05 eV), (110)-B(2) site (−4.81 eV), and (111)-H site (−5.03 eV), with the adsorption strength governed by the surface coordination environment. The adsorption energies of O atoms (−4.5 to −8.2 eV) are significantly higher than those of O₂ molecules. The order of the most stable O atom adsorption sites is (110)-B(2) site (−8.22 eV) > (100)-H site (−6.97 eV) > (111)-T(U) site (−5.09 eV), which differs from that of O₂, revealing the efficient O atom trapping effect of the groove structure on the (110) surface. Electronic structure analysis indicates that upon O atom adsorption, the work functions of the (100) and (110) surfaces increase by 0.62 eV and 0.39 eV, respectively, while that of the (111) surface decreases by 0.57 eV, suggesting that the (111) surface is more susceptible to further oxidation. In terms of bonding mechanisms, the interaction between O and U is primarily dominated by p–d hybridization between O-2p and U-6d orbitals. The U-5f orbital participates indirectly through f–d coupling with U-6d, while direct p–f hybridization is enhanced in the case of isolated O atom adsorption. This study provides an atomic-scale theoretical basis for understanding the initial oxidation mechanism of UN surfaces and offers important guidance for the surface protection design of UN-based nuclear fuels. Full article

First-principles DFT calculations have been employed to examine the hydrogen storage behavior of Ca-decorated silicene. A single Ca atom binds to the hollow site of the silicene monolayer with a binding energy of −2.348 eV, the magnitude of which exceeds the cohesive energy of bulk Ca, thus preventing Ca clustering. Pristine silicene interacts weakly with H₂, with an adsorption energy of only −0.047 eV, while Ca decoration notably enhances the binding affinity to −0.561 eV. Each Ca site can accommodate up to five H₂ molecules through a Kubas-like interaction, with an average adsorption energy of −0.327 eV. With Ca atoms decorating both sides of the silicene, the system delivers a hydrogen storage capacity of 7.5 wt% and complete H₂ release at approximately 380 K as revealed by AIMD simulations. Our findings suggest that Ca-decorated silicene could serve as a viable material for reversible hydrogen storage applications. Full article

Defect calculations for semiconductors demand both large supercells and accurate electronic structures, posing a significant challenge to first-principles methods. Conventional density functional theory (DFT) with local or semi-local exchange-correlation functionals severely underestimates the band gap, whereas hybrid functionals such as HSE06 provide higher accuracy but at a substantially increased computational cost. In this work, we demonstrate that shell DFT-1/2, a self-energy correction method for electronic structure calculations, may be used jointly with HSE06 to reach the optimal efficiency as well as accuracy. In particular, indium phosphide (InP) was taken as an example. The shell DFT-1/2 method was utilized to yield accurate band structures with a 1.44 eV direct gap, without any empirical parameter. Subsequently, the portion of exact exchange was tuned to match the shell DFT-1/2 electronic structure in HSE06 calculations. The charge transition levels of various point defects in InP were derived using HSE06, and HSE06 and shell DFT-1/2 may be employed alternatively to yield the density of states for the defective supercells. Their consistency proves the feasibility of the complementary employment of the two methods, and this strategy is readily extendable to other semiconductor research. Full article

The optoelectronic properties of the lead-free perovskite CsSn_0.5Ge_0.5I₃ are investigated by first-principles calculations and numerical simulations using SCAPS-1D. The energy-level alignment between transport layers and the perovskite layer is evaluated, resulting in the establishment of the PCBM/CsSn_0.5Ge_0.5I₃/PEDOT:PSS structure. Key parameters, including bulk defect density, layer thickness, and electrode materials, are optimised, and the effects of resistance, illumination intensity, thermal stability, and carrier generation-recombination rates on device performance are analysed. The optimal device structure FTO/PCBM/CsSn_0.5Ge_0.5I₃/PEDOT:PSS/C achieves a power conversion efficiency (PCE) of 24.50% and a fill factor (FF) of 80.01%. Machine learning (ML) algorithms are applied to predict photovoltaic parameters, with Random Forest (RF) exhibiting the highest accuracy. SHAP analysis identifies absorber layer thickness as the dominant factor influencing efficiency, providing guidance for experimental optimisation. This integrated approach offers a practical pathway for designing high-performance, stable, and environmentally sustainable perovskite solar cells (PSCs). Full article

Commercial aluminum (Al) metals contain unavoidable impurities, such as iron (Fe) and silicon (Si). Due to its low solubility and high chemical affinity to Al, Fe exists in the form of Fe-containing intermetallic compounds (Fe-IMCs), which are crucial in solidification processes, determining the micro-structure and consequently the mechanical performance of the cast parts. Meanwhile, Si, as an impurity or addition, may join the binary Fe-IMCs. Here, we investigate the Si stabilization effects on the frequently observed Al-rich Fe-IMCs in a comprehensive and systematic way using a first-principles density-functional theory (DFT) approach. The study reveals different Si stabilization effects on the cubic α- and hexagonal α’-phase, as well as other binaries: Al₁₂Fe, η-Al₆Fe, τ₄-, β-, and θ-phases. The enhancement of stability for the α-phase is moderate, while it is strong for the α’-phase. For the stability series (from higher to lower) is θ-Al₁₃Fe₄ > η-Al₆Fe > α-Al₄.₇₅Fe in the binary system, while it becomes τ₄-(Al,Si)₅Fe > β-Al₄.₅SiFe > α’-(Al,Si)₄.₁₇₄Fe for the ternary Fe-IMCs. The information obtained here helps understand the formation of Fe-IMCs particles during casting of Al-Si alloys, and the design of novel Al alloys of fine micro-structures and desired mechanical performances of the products from the primary Al and the scraps and wastes. Full article

Contact electrification (CE), also referred to as triboelectrification, describes electron transfer occurring at the interface of dissimilar materials. Its microscopic mechanism remains unclarified due to the complex coupling of multiple physical fields, yet the rapid development of triboelectric nanogenerators (TENGs) has rendered CE a prominent research hotspot in tribology on account of its promising application prospects. Metal/polymer combinations have been widely employed for CE research due to their significant differences in electron gain and loss. Nevertheless, most existing studies focus solely on saturated polymers, and systematic comparative analyses between saturated and unsaturated molecular structures are rarely reported. Accordingly, the intrinsic microscopic origin of enhanced interfacial electrification performance induced by unsaturated groups has not been fully understood. In this work, first-principles calculations based on density functional theory (DFT) are implemented to establish interfacial models consisting of an Al substrate and three types of PTFE single chains: fully saturated-PTFE, PTFE with unsaturated bonds at the chain terminus, and PTFE with unsaturated bonds in the middle of the chain. The inherent mechanism governing the modulation of CE behaviors by unsaturated structures are comprehensively revealed from multiple perspectives, including charge transfer, electrostatic potential, and frontier orbital distribution. Computational results demonstrate that unsaturated groups drastically elevate local electrostatic potential and strengthen the electron-trapping capability of molecular chains, thereby substantially boosting CE performance. Moreover, this modulation effect exhibits remarkable position dependence, where unsaturated structures located in the middle of molecular chains deliver better performance improvement than terminal unsaturated moieties. The electron-donating and electron-accepting properties of materials are dominated by the energy level characteristics of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), respectively. This study elucidates the microscopic mechanism of CE at unsaturated polymer/metal interfaces at the molecular scale, and provides theoretical support for optimizing the output performance of TENGs through surface modification strategies. Full article

Hard carbon (HC) is one of the most promising anode materials for sodium-ion batteries (SIBs). Yet its sodiation mechanism—particularly the origin of the sloping and plateau regions in the voltage–capacity curve—remains debated. In this work, first-principles density functional theory (DFT) calculations are employed to systematically investigate the sodium storage mechanism at the edges and within the interlayer ultramicropores of bilayer graphene nanoribbons (BGNRs) with zigzag (BGNRs-Z) and armchair (BGNRs-A) terminations. A series of edge models, including hydrogenated, dehydrogenated (dangling bond), monovacancy (MV), and divacancy (DV) defects, were constructed to elucidate the effects of edge type and defect species on Na adsorption and intercalation. Our results demonstrate that Na ions preferentially adsorb at the edges rather than in the interior interlayer regions. The zigzag edge exhibits stronger binding affinity toward Na than the armchair edge. Progressive Na intercalation gradually opens the edge interlayer spacing. It reduces the interlayer angle toward a parallel configuration and accompanies a stacking transition from AB to AA at higher Na concentrations. Edge dangling bonds significantly enhance Na binding and drive the initial separation of edge carbon layers, whereas surface MV and DV defects contribute to Na adsorption at lower binding strengths. The calculated voltage–capacity relationships reveal that the first sloping region (>1.0 V) is primarily associated with Na adsorption at zigzag and defective edges, the second sloping region (0.1–1.0 V) can be rationalized by combined surface defect adsorption and interlayer intercalation, and the low-voltage plateau (<0.1 V) is thermodynamically linked to Na filling of narrow slit pores with optimized interlayer distances (~4.0 Å for zigzag and ~4.3–5.8 Å for armchair edges). These findings establish a direct structure–property correlation between carbon microstructure (edge type, defect architecture, and pore geometry) and the electrochemical voltage profile, offering atomic-level insights for the rational design of high-performance carbon-based anodes for SIBs. Full article

In this work, we performed a comprehensive first-principles investigation of the electronic structure, charge carrier relaxation dynamics, and photoluminescence properties of Rh-doped BaTiO₃, with a focus on photocatalytic water splitting applications. By combining hybrid DFT (HSE06), DFT+U, and Redfield theory, we elucidated how the doping site (Ti vs. Ba), dimensionality (bulk vs. surface), and aqueous environment govern the nonequilibrium behavior of photogenerated electron–hole pairs. Rh occupying Ti sites on the (001) surface exhibits a unique combination of extended visible-light absorption, ultrafast non-radiative relaxation, and efficient charge separation. These characteristics establish it as a promising photoanode material for photoelectrochemical water splitting. Full article

First-principles calculations based on density functional theory (DFT) were employed to investigate the binding energy, work function, electronic structure, and optical properties of carbon quantum dots (CQDs) and nitrogen-doped carbon quantum dots (NCQDs) loaded on the TiO₂(101) surface. The results indicate that NCQDs exhibit stronger binding affinity to the TiO₂(101) surface than CQDs. The charge transferred from CQDs to the TiO₂(101) surface mainly originates from the carbon atoms located at the two ends along the a-axis of the CQDs. By contrast, the charge distribution between NCQDs and TiO₂(101) is more uniform, with the Bader charges of the carbon atoms at the two ends along the a-axis in NCQDs being reduced to varying degrees compared to those in CQDs. Moreover, loading NCQDs is more favorable for the generation of photogenerated electron-hole pairs and electron transfer, whereas loading CQDs leads to the smallest band gap. Full article

The growing demand for efficient, stable, and environmentally friendly materials for next-generation optoelectronic and photovoltaic applications has attracted significant interest in double perovskite compounds. First-principles density functional theory (DFT) calculations were performed to systematically investigate the structural, mechanical, electronic, and optical properties of Ba₂MReO₆ (M = Li, Na, K, and Rb) double perovskites. Structural optimization confirms that all compounds crystallize in the cubic Fm3̅m symmetry. The thermodynamic and geometric stability of the series is checked with negative formation energies and tolerance factor analyses (t, μ, τ). Mechanical analysis confirms that all compounds are mechanically stable; Ba₂LiReO₆ is the stiffest, while Ba₂RbReO₆ shows moderate stiffness with the highest ductility. Furthermore, ab initio molecular dynamics (AIMD) simulations at room temperature confirm the dynamical stability of all compounds, with negligible fluctuations in total energy under thermal conditions. The calculated band structures using both GGA-PBE and HSE06 hybrid functionals reveal that all compounds possess indirect band gaps, with HSE06 values of 2.236 eV for Ba₂LiReO₆, 2.133 eV for Ba₂NaReO₆, 2.116 eV for Ba₂KReO₆, and 1.395 eV for Ba₂RbReO₆. Optical measurements indicate that it is highly polarizable by dielectric polarizability, has high absorption coefficients (approximately 10⁶ cm⁻¹), and has large optical conductivity in the UV, with large inter-band interactions between 2 and 4 eV. The suitable band gap and favorable optical characteristics suggest that Ba₂RbReO₆ is the most promising candidate for photovoltaic and solar-cell applications. Full article

To address the insufficient visible-light absorption of Bi₄O₅Br₂ photocatalysts, first-principles density functional theory (DFT) calculations were employed to systematically investigate the effects of I doping at different concentrations (12.5%, 25%, 50%, 75%, 87.5%, and 100%) on the geometric structure, electronic structure, optical properties, and photocatalytic CO₂ reduction performance of Bi₄O₅Br₂. Formation energy calculations and Ab initio molecular dynamics (AIMD) simulations indicate that the I-doped systems possess good thermodynamic and kinetic stability. Geometric analysis shows that I doping leads to a gradual expansion of lattice parameters along the c-axis (from 14.80 Å to 15.16 Å), due to the larger ionic radius of I⁻ compared to Br⁻. Electronic structure results reveal that all doped systems remain indirect band gap semiconductors, with the band gap decreasing from 2.56 eV for the pristine system to 2.25 eV at 87.5% doping. This reduction is mainly attributed to the progressive substitution of Br 4p states by I 5p states near the valence band maximum, which modifies the valence band structure. Differential charge density analysis shows electron transfer from Bi to I, enhancing local polarization effects. Optical property calculations demonstrate a pronounced red shift in the absorption edge and significantly enhanced absorption intensity in the visible region after I doping. The real and imaginary parts of the dielectric function also exhibit red shifts and increased peak intensities in the low-energy region. Gibbs free energy analysis indicates that the Gibbs free energy for *COOH formation decreases from 2.83 eV in the pristine system to 2.68 eV after I doping, while the free energy of the *CO intermediate decreases from 1.28 eV to 0.98 eV, significantly improving the CO₂ reduction pathway. This study provides a theoretical basis for improving the optical response and the thermodynamics of the CO₂ reduction reaction through halogen substitution, suggesting a promising strategy for enhancing the photocatalytic potential of Bi₄O₅Br₂. Full article

Accurate prediction of hydrogen storage properties is needed for accelerating the design of body-centered cubic (BCC)-type V-based alloys, where the composition–property space is too large for trial-and-error experimentation alone. Here we report a stacking ensemble framework that combines XGBoost, Random Forest, Extra Trees, and Gradient Boosting as base learners with linear or ridge meta-learners, with hyperparameters tuned by a genetic algorithm (GA). Three descriptor strategies are compared across seven target properties: composition-only (C), property-only (P), and composition–property fusion (CP). On target-specific subsets containing 95–901 experimental records and 17 alloying elements (the smallest subset, 95 records, corresponds to maximum hydrogen capacity $C_{\max }$, which may limit model stability for that property), the best model for each target gives $R^2$ values from 0.865 to 0.981 (all metrics are from five-fold cross-validation; no independent external test set was employed); the P-type model for desorption plateau pressure reaches $R^2=0.981$. SHapley Additive exPlanations (SHAP) analysis shows that physically derived descriptors, including valence electron concentration, atomic size mismatch, and electronegativity difference, dominate in P and CP models, whereas Ti and Cr contents are the leading compositional features. A Non-dominated Sorting Genetic Algorithm II (NSGA-II) optimizer then ranks 3000 final candidate alloy compositions in six alloy families using four objectives: high predicted retention, high predicted cycle count, high predicted BCC phase ratio, and a low cost proxy; these candidates represent model-based predictions and await experimental synthesis and cycling validation. The V–Ti–Cr–Fe–Mn system contains the largest number of candidates with predicted retention above 99%, while Ti-free V–Cr–Fe–Mn–Al alloys provide low-cost alternatives in the model search space. First-principles calculations on four representative alloys only show that BCC structures are lower in energy than FCC structures by about 0.08–0.13 eV/atom and that hydrogenated structures exhibit clear charge accumulation around H sites, supporting the physical plausibility of the data-driven screening results, though density functional theory (DFT) validation does not replace experimental measurement of PCI curves and cyclic stability. Full article

The structural, electronic, and magnetic properties of the PdRSb, usually also referred to as RPdSb, ($R=$ La-Lu) semi-Heusler compound series have been systematically investigated using first-principles calculations based on Density Functional Theory (DFT). Our structural optimizations reveal that the cubic $C{1}_{\mathrm{b}}$ A-type variant is the energetically most favorable and thermodynamically stable ground state across the entire series. The calculated equilibrium lattice constants follow the well-known lanthanide contraction trend, with the exception of the Yb-based compound, which displays an anomalous lattice expansion. Magnetic stability analysis demonstrates that the magnetism is highly localized at the rare-earth (R) sites and closely follows the progressive filling of the $4f$ shell, peaking at $7{\mathsf{\mu }}_{\mathrm{B}}$ for PdGdSb, while PdLaSb, PdYbSb, and PdLuSb remain non-magnetic. Furthermore, our electronic structure calculations reveal a rich variety of behaviors: PdLaSb and PdLuSb behave as gapless semiconductors, while most of the magnetic compounds exhibit near half-metallic characteristics. Notably, PdCeSb is predicted to be a perfect half-metal with an integer magnetic moment of $1{\mathsf{\mu }}_{\mathrm{B}}$. These findings highlight the significant chemical tunability of the PdRSb family, positioning them as promising candidates for future applications in spintronics and magnetoelectronics. Full article