Vacancy-screw dislocation interactions in bcc Nb are studied with near density functional theory accuracy using a machine-learning potential, specifically a moment tensor potential (MTP), in large-scale atomistic simulations. The MTP predicts attractive vacancy-dislocation interactions with threefold symmetry in the (111) plane. These attractive interactions lead to a decrease in the Peierls stress by up to 28%, depending on the vacancy position relative to the dislocation. The interactions also lead to the formation of new complex topological defects (CTDs), when the vacancy is close to the dislocation core. A CTD can be geometrically characterized as a screw dislocation with multiple kinks and with a (partially) dissociated vacancy along the dislocation line. CTDs form under shear when the vacancy-dislocation distance is less than ∼6 $\AA$, providing a new mechanism for pinning screw dislocations. The formation of CTDs confirms theoretical predictions made in the early 1990s based on differential geometry and underscores the importance of machine-learning potentials and large-scale simulations for accurately describing the properties of extended defects in metals.

Ni-based catalysts are promising alternatives to Pt for the hydrogen evolution reaction (HER), and topological Ni-based materials are particularly appealing because their robust nontrivial surface states can enhance charge transfer and intermediate adsorption. Motivated by these advantages, our high-throughput computational screening of the latest Materials Project database identifies 46 Ni-based potential topological HER catalysts, exhibiting a Gibbs free energy change $|\mathrm{\Delta }{G}_{{\mathrm{H}}^{*}}|<$ 0.2 eV. Furthermore, we have conducted a detailed study of two representative candidates, ${\mathrm{Ni}}_3\mathrm{Ge}$ and NiBi, which show $|\mathrm{\Delta }{G}_{{\mathrm{H}}^{*}}|$ of 0.117 and 0.08 eV, respectively. By considering different surfaces and tuning the corresponding bulk topology via strain or doping, we show that catalytic performance scales with the density of topological surface states, which strongly influences charge transfer during the HER process. These findings establish a strong correlation between topological electronic structure and HER activity, providing a predictive descriptor and a general strategy for the design of efficient topological HER catalysts.

Understanding and overcoming the bottlenecks that limit carrier mobility in wide-band-gap III-nitrides is essential for advancing high-performance electronic and optoelectronic technologies. Here we employ state-of-the-art ab initio Boltzmann transport calculations, incorporating fully resolved electron-phonon interactions, to evaluate the carrier mobilities of GaN and AlN in their wurtzite, hexagonal, and haeckelite (4|8) phases. We identify a robust mobility ordering of haeckelite > wurtzite > hexagonal for both electrons and holes, with mobility enhancements exceeding 50–250% in the haeckelite phases. By analyzing mode- and energy-resolved scattering spectra, we demonstrate that this improvement originates from a symmetry-driven suppression of piezoelectric acoustic scattering when the noncentrosymmetric wurtzite lattice transforms into the centrosymmetric haeckelite structure. In the absence of piezoelectric coupling, acoustic scattering reduces to deformation-potential behavior, while optical scattering becomes the dominant channel. The resulting decrease in low-energy scattering rates produces markedly enhanced mobilities, particularly for holes, where traditional III-nitride materials have long faced intrinsic limitations. Our findings reveal phase engineering as an effective route to mitigating phonon-limited transport in III-nitrides and suggest haeckelite structures as promising candidates for next-generation high-mobility electronic and quantum devices.

Density functional theory (DFT) provides a powerful tool for describing the electronic properties of materials, however, self-interaction errors in semilocal functionals complicate the accurate modeling of correlated materials. The $\mathrm{DFT}+U$ method is a popular and computationally cost-effective solution for mitigating self-interaction; though, this reduces the ab initio aspect of DFT calculations, as the outcome now becomes dependent on the user's choice of $U$ parameters. Atomistic modeling of plutonium dioxide (${\mathrm{PuO}}_2$) is employed to provide insight into its evolution in storage or into its properties as mixed-oxide fuel. There is no single $U$ parameter that can reproduce all the experimental properties of ${\mathrm{PuO}}_2$ accurately and, as such, it is important that the $U$ parameter is selected with careful consideration. In this work, we use noncollinear $\mathrm{DFT}+U$ simulations to thoroughly examine the defect chemistry of ${\mathrm{PuO}}_2$ using $U=4$ and $7\mathrm{eV}$, in order to understand the implication the choice of $U$ parameter can have on the predicted defect chemistry. We find that both $U$ parameters predict the same intrinsic defect chemistry, with the main discrepancy being on the preferred charge state of the oxygen vacancies: $+2$ for $U=4\mathrm{eV}$ and neutral for $U=7\mathrm{eV}$. Additionally, we show that the choice of $U$ can impact the defect formation energies and preferred charge states of a dopant. When uranium is placed onto a plutonium lattice site, it tends to favor the neutral and $+1$ charge state (indicative of ${\mathrm{U}}^{4+}$ and ${\mathrm{U}}^{5+}$) with $U=4\mathrm{eV}$, whereas with $U=7\mathrm{eV}$ the $-1$ and neutral charge states are more stable.

Structural, thermodynamic, and electrical transport properties of TbAuPb were investigated on single crystals. The compound was found to crystallize with the cubic MgAgAs-type structure characteristic of half-Heusler materials. It orders antiferromagnetically at $T_{\mathrm{N}}=5\mathrm{K}$ and undergoes a transition into a different antiferromagnetic phase emerging in high magnetic fields. Electrical transport in TbAuPb exhibits a multiband character, with a predominance of hole-like carriers. Angular magnetoresistance evolves systematically with applied magnetic field and changes its symmetry near the spin-reorientation transition, highlighting strong coupling between the charge transport and the magnetic order. The results of first-principles calculations indicate that TbAuPb is a band inverted semimetal in the nonmagnetic state, which becomes topologically trivial in the field-induced ferromagnetic state.

We employ atomistic machine-learning simulations to explore the atomic structures resulting from buckyball-graphene sandwich systems, where ${\mathrm{C}}_{60}$ molecules are confined between graphene layers under high temperature and pressure. We find that, depending on the thermodynamic conditions, ${\mathrm{C}}_{60}$ molecules can transform into dimers, trimers, and fullerene peanuts, as well as collapse into two- and three-dimensional amorphous condensed phases, including amorphous graphene and amorphous diamond. All of these forms have different electronic properties. Notably, the graphene layers maintain their structural integrity well with minimal changes, collapsing only under the most extreme conditions explored. Our study provides a unified framework for understanding the atomistic properties of fullerene-derived nanomaterials consistent with experiments and their dependence on the synthesis conditions. These findings suggest that graphene could function as an effective nanoscale “reactor” to synthesize novel carbon-based materials with diverse properties using ${\mathrm{C}}_{60}$ as a precursor.

The microstructural characteristics and morphology of interfaces in metals can be crucial in governing the initiation of plasticity and early deformation mechanisms under extreme conditions. During high-strain-rate deformation, these interfaces significantly affect dislocation nucleation, twinning, and other mechanisms that directly impact material strength and failure. Despite their importance, a substantial knowledge gap remains between the observed macroscopic material behavior and the underlying role of bimetal interfaces in plasticity initiation. To address this gap, large-scale molecular dynamics simulations are performed on Al/Ti bimetal structures to examine the effect of interface characteristics on the onset of plasticity under uniaxial compression. Specifically, this study investigates how interface roughness (flat vs waveform interfaces) modifies the initiation of plastic events in the microstructure. Atomistic simulations indicate that interface roughness (a microscopic behavior) reduces the stress required for dislocation nucleation, thereby reducing the peak stress relative to a flat interface. For the square interface, the step height strongly influences plasticity initiation by setting the separation of locally flat regions. Varying the interface rotation relative to the loading direction (macroscopic behavior) reveals that the peak stress for both flat and waveform interfaces initially decreases and then increases with rotation, accompanied by a shift in dominant mechanisms—from Al twinning (flat) to interface sliding and Ti-dominated phase transformation and twinning at lower angles. The change in the stress-strain slope during initial compression reflects how rotation alters the resolved shear stress and activates different slip systems. Overall, the study provides valuable insights into the role of bimetal interfaces in controlling plasticity initiation and early deformation pathways for Al/Ti under extreme loading conditions.

Theoretical modeling of bonding dynamics in metal oxides is required for predicting their thermal conductivity, catalytic activity, and mechanical properties. A primary challenge is the scarcity of experimental methods for validating theoretical predictions of these atomic-scale dynamics. This work presents a workflow that uses experimental extended x-ray absorption fine structure (EXAFS) data collected at high temperatures to validate an interatomic force field for uranium dioxide ($\mathrm{U}{\mathrm{O}}_2$), an important model material. The validated force field is then used to drive computationally intensive molecular dynamics (MD) simulations and as input for the much faster dynamical matrix Debye-Waller (DMDW) method. The predicted values of the Debye-Waller factors from the DMDW calculations are in good agreement with those obtained from the MD simulations, with residual pair-specific differences attributable to quantum zero-point motion at low temperatures and lattice anharmonicity at high temperatures. We further show that theoretical EXAFS spectra constructed directly from DMDW-derived Debye-Waller factors reproduce the experimental data (at relatively low temperatures) with accuracy comparable to full MD-EXAFS, providing an additional validation of the choice of the potential. This study establishes a validated, rapid computational pathway for modeling bond dynamics, naturally incorporating quantum nuclear statistics absent in classical simulations, which are essential for the mechanistic understanding of complex oxide materials.

Stacking faults and other topological defects in ferroics can have a significant influence on the electronic and mechanical properties of the material. Here, regular stacking faults in the tetragonal tungsten bronze material ${\mathrm{Sr}}_2{\mathrm{NaNb}}_5{\mathrm{O}}_{15}$ are investigated through transmission electron microscopy, symmetry mode analysis, and machine-learned force-field calculations. It is shown that the faults, with a fault vector of $\frac{1}{4}{\left[\overline{2}12\right]}_o$, annihilate in sets of four in the material, owing to the ¼ unit cell displacement along the b-axis. The four resulting domains emerge as four possible directions of the ${\mathrm{S}}_3$ order parameter, related to ${\mathrm{NbO}}_6$ octahedral tilts in the material. Force-field calculations reveal that the stacking faults are likely placed at positions where the octahedra in neighboring domains have similar magnitudes of rotation, and that the estimated stacking fault energy is 46 $\mathrm{mJ}/{\mathrm{m}}^2$. The investigation shows that the stacking faults have a local effect on the in-plane polar mode present in the structure, and therefore could affect the ferroelectric properties.

Sodium niobate ($\mathrm{NaNb}{\mathrm{O}}_3$, NN), as a rare room-temperature antiferroelectric material, exhibits significant applications in important fields such as pulse energy storage and multistate nonvolatile memories. However, pristine NN generally suffers from an irreversible field-induced phase transition, which prevents the observation of the characteristic double hysteresis loops of antiferroelectrics. Previous findings have revealed that its unstable antiferroelectric structure is strongly correlated with the occupancy instability of $\mathrm{N}{\mathrm{a}}^{+}$ ions under external fields. $\mathrm{N}{\mathrm{a}}_{1-3x}\mathrm{L}{\mathrm{a}}_x\mathrm{Nb}{\mathrm{O}}_3$ system is constructed in this work via doping the Na site with $\mathrm{L}{\mathrm{a}}^{3+}$, which differs obviously from $\mathrm{N}{\mathrm{a}}^{+}$ in both mass and electronic structure. This strategy aims to realize a progressive evolution from irreversible to reversible phase transition under electric fields, by controlling the doping concentration of $\mathrm{L}{\mathrm{a}}^{3+}$. Based on the precise identification of Raman spectroscopy for phonon vibrations, the in situ Raman spectra under varying electric field and temperature are measured to conduct a detailed insight into the evolution pathways of multiple crucial phonons in samples. Accordingly, the modulation of $\mathrm{L}{\mathrm{a}}^{3+}$ on the reversibility of field-induced phase transition could be effectively deciphered. This work reinterprets the unique field-induced phase transition in NN-based materials from the perspective of phonon evolution, which lays an important research foundation for the design and development of NN-based devices with multiple transitions between different electrical ordering states.

High-quality InAs quantum wells grown on InP are a promising platform for topological quantum information processing due to their large $g\text{−}\mathrm{factor}$, strong Rashba spin-orbit interaction, and their compatibility with in situ deposited superconductors. In this work, we investigate InAs/InGaAs quantum wells grown on InP (001) wafers, focusing on how the layer structure and strain influence the electronic properties and surface morphology. By combining quantum transport measurements with atomic force microscopy, we show that the layer design predominantly affects the mobility anisotropy, which aligns well with the surface morphology. Surface characterization further reveals the mechanism of quantum well collapse when the layer thickness exceeds the strain limit. In addition, transport measurements demonstrate that quantum confinement has a clear impact on band nonparabolicity.

Carbide particles act as effective hydrogen traps that can mitigate hydrogen embrittlement in steels, with their trapping efficacy governed by the binding energy of hydrogen at atomic-scale sites within the carbide and at the carbide/matrix interface. Within the carbide, carbon vacancies are established trap sites, while at the carbide/matrix interface, multiple distinct trap sites may form depending upon the interface character. State-of-the-art experimental methods cannot attribute binding energies to individual sites unambiguously, particularly at the carbide/matrix interface, where distinct trap sites may exhibit similar binding energies. Density functional theory (DFT) calculations have partially addressed this limitation, but their computational cost prohibits accurate treatment of semicoherent and incoherent interfaces, for which hydrogen binding energies remain poorly characterised. In this work, we develop a DFT-accurate machine-learning Fe–TiC–H interatomic potential that enables simulations of hydrogen energetics and kinetics at various TiC/Fe interfaces in the Baker–Nutting orientation. Predictions of structural, dynamic and energetic properties of both bulk phases (i.e., bcc Fe and rocksalt TiC) and the coherent interface with and without hydrogen are in good agreement with DFT. We apply the potential to examine the atomic structure and hydrogen trapping at semicoherent and incoherent interfaces. We find that the binding energy of hydrogen at misfit dislocations is similar to that at coherent interfaces, with a difference of no more than 0.1 eV. However, the misfit strain field reduces carbon vacancy formation energies at the interface, where hydrogen can be trapped with similar binding energies as that in a bulk C vacancy (approximately –1 eV). Lower vacancy formation energies are also found at the incoherent interface, where hydrogen binding energies span a broader range, depending sensitively on the local atomic environment. Overall, the results enable interpretation of experimental observations of hydrogen segregation around semicoherent and incoherent TiC interfaces.

An electron diffraction (ED) and high-resolution transmission electron microscopy (HRTEM) study of the semiconductor system $2\mathrm{PbS}+{\mathrm{NaSbS}}_2$ $\left({\mathrm{NaPb}}_2{\mathrm{SbS}}_4\right)$ reveals strikingly complex, nanostructural properties despite its simple NaCl-type framework. We uncover the coexistence of commensurate and incommensurate cation ordering, nanoscale defect architectures, and quasiperiodic arrays of antiphase boundaries. In many areas, the dominant observed structure type corresponds to the NaCl type, with varying lattice parameters, denoting inhomogeneities in composition. In other areas, superstructure reflections were observed in the ED patterns. The HRTEM images reveal the existence of different nanocrystals, with long-range ordering of the cations. Three different commensurate modulated structures (superstructures) of the NaCl type of structure were observed. All the nanocrystals with ordering were observed to grow endotaxially within the matrix. Moreover, the local arrangement of several defects (orientation variants and antiphase boundaries) in a quasiperiodic way leads to the local formation of incommensurate modulated structures. Finally, in some cases, diffuse scattering intensity was observed in the ED patterns. The HRTEM images, together with the ED results, reveal a transition state between the phases with long- and short-range order. These findings clarify the structural behavior of this complex semiconductor and motivate further investigation of its structural and physical properties.

Physical properties in the normal and superconducting (SC) state are investigated with ${}^{125}\mathrm{Te}$-nuclear magnetic resonance (NMR) measurements in a quasicrystal ${\left({\mathrm{Ta}}_{0.95}{\mathrm{Cu}}_{0.05}\right)}_{1.6}\mathrm{Te}$, which was a recently discovered superconductor with the SC transition temperature $T_{\mathrm{c}}=0.94 \mathrm{K}$. The nuclear spin-lattice relaxation rate $1/T_1$ shows a coherence peak just below $T_{\mathrm{c}}$, followed by an exponential decrease down to 0.1 K. The overall temperature dependence of $1/T_1$ is in good agreement with an $s$-wave SC model with an SC gap slightly smaller than the BCS value. However, the coherence peak is unusually small, which may be attributable to a reduced Bogoliubov peak theoretically predicted for quasicrystals. Furthermore, ${}^{125}\mathrm{Te}\text{−}\mathrm{NMR}$ spectra show marginal shift and almost no linewidth broadening below $T_{\mathrm{c}}$, revealing unusual superconducting responses in this quasicrystal.

Metal Phthalocyanine-based materials are known for their stability and are widely used in flexible organic electronics. The study presented here investigates the impact of substrate temperature on the growth to control the crystallinity of the deposited copper phthalocyanine (CuPc) thin films on silicon substrates and its effect on the charge transport in $\mathrm{Au}/\mathrm{CuPc}/n$-Si heterostructures. Current-voltage $\left(I\text{−}V\right)$ characterization of the heterostructures reveals the appearance of multiple transport mechanisms, ranging from direct and Fowler-Nordheim tunneling at lower temperatures to Poole-Frenkel conduction at higher temperatures, depending on the crystallinity of the deposited CuPc films. Resonant tunneling observed in the amorphous thin film suggests the existence of a $\pi$-electron bridge parallel to the vertical charge transport path. Such orientation of CuPc molecules is important for efficient charge extraction in organic solar cells.