We present a fine-tuned machine learning interatomic potential (MLIP) for all inorganic halide perovskites $\left(A{A}^{\prime }B{B}^{\prime }{X}_6\right)$, which we use to investigate stability trends across 195 968 charge-balanced compositions. The MLIP accurately predicts the relative stability of cubic and distorted phases, capturing octahedral tilting effects that often favor lower-energy or nonperovskite ground states. For the entire set of examined materials, only 2% of compositions are metastable $(\mathrm{\Delta }{\mathrm{H}}_d< 100 \mathrm{meV}/\text{atom})$ in the high-symmetry cubic phase. To rationalize this result, we analyze 23 730 ${\mathrm{Cs}{\mathrm{A}}^{\prime }\mathrm{B}{\mathrm{B}}^{\prime }\mathrm{X}}_6$ compositions and show that stability in the cubic phase correlates with the size mismatch between $A$ and $A^{\prime }$ cations. Because the MLIP yields DFT-quality optimized structures, single-point DFT can be used efficiently to compute energies and band gaps. Assuming the cubic structure instead of the ground state structure, which typically contains various degrees of octahedral distortions, can lead to changes in the band-gap energy of up to 0.50 eV. The MLIP enables vibrational free-energy calculations via phonon density of states, allowing temperature-dependent phase stability predictions. These reveal several compounds that are predicted to transition from the (distorted) ground state phase (at $T=0\mathrm{K}$) to high-symmetry cubic phases at elevated temperatures. Overall, this work provides a tool and dataset of DFT quality $A{A}^{\prime }B{B}^{\prime }{X}_6$ structures for analyzing key $\mathrm{structure}-\mathrm{property}$ relationships and supports the discovery of new perovskite compositions with more realistic stability and band-gap estimates than considering the cubic phase alone.

Uranyl molybdates are important materials for the pyrochemical reprocessing of spent nuclear fuel. Progress in first-principles atomistic modeling and simulation of these materials is desirable but complicated by the presence of $f$ electrons, the effects of strong electron correlations, and the scarcity of experimental data for the validation of models. In this work, we present a first-principles model of solid-phase uranyl molybdates based on the DFT + U level of theory. Initially, pure ${\mathrm{UO}}_2{\mathrm{MoO}}_4$ is synthesized, characterized, and diffuse reflectance spectroscopy is utilized in order to facilitate the validation of such a first-principles model, which is then applied to various sodium-bearing uranates, molybdates, and uranyl molybdates. Crystal structures and formation enthalpies are considered as well as the electronic properties of ${\mathrm{UO}}_2{\mathrm{MoO}}_4$ and the polymorphism of ${\mathrm{Na}}_2{\mathrm{UMo}}_2{\mathrm{O}}_{10}$. Apart from ${\mathrm{UO}}_2{\mathrm{MoO}}_4$, we present independent experimental results for ${\mathrm{Na}}_2{\mathrm{UMo}}_2{\mathrm{O}}_{10}$ by solving controversies in the numerous structural data attributed to this compound.

Frustrated magnetic materials with competing interactions are a rich source of novel emergent phenomena, as frustration inhibits long-range order and may give rise to a quantum spin liquid (QSL) behavior with strong quantum entanglement, topological order, and often fractionalized excitations. Here, we report an in-depth Raman spectroscopic analysis to probe a single crystal of a rare-earth triangular-lattice antiferromagnet, $\mathrm{YbMgGa}{\mathrm{O}}_4$, along the $ab(/ac)$ crystallographic planes. $\mathrm{YbMgGa}{\mathrm{O}}_4$ has recently attracted significant interest as a promising gapless U(1) QSL candidate with a spinon Fermi surface. We observe an underlying broad continuum of excitations, with a possible origin in disorder arising from $\mathrm{M}{\mathrm{g}}^{2+}/\mathrm{G}{\mathrm{a}}^{3+}$ site mixing and a broad distribution of crystal field excitation (CFE) parameters, rather than a single set of well-defined levels. The development of the Fano asymmetry in the low-frequency phonon mode indicates the coupling with the underlying continuum. These underlying excitations are also reflected in the dynamic spin susceptibility estimated from the Raman response. The apparent renormalization of the phonon self-energy parameters at $\sim 50$ K, which are ascribed to the phonon decaying into itinerant underlying continuum excitation from structural disorder, arises with $\mathrm{M}{\mathrm{g}}^{2+}/\mathrm{G}{\mathrm{a}}^{3+}$ site mixing. Additionally, we analyze the angle-resolved polarization measurements for both $ab(/ac)$ crystallographic planes to decipher the symmetry of the phonons, CFEs, and underlying excitations. The observed variations of the phonon mode behavior as a function of incident photon polarization provide evidence of anisotropic light-matter interactions along with the anisotropy in the spin susceptibility, spin-spin correlation length, and phonon renormalization.

We report a comprehensive study of the ternary compound ThIrSn, characterized by a distorted kagome lattice of Th atoms in polycrystalline form. The compound adopts a noncentrosymmetric ZrNiAl-type crystal structure, with cell parameters $a=b=7.5097\left(4\right)\AA$ and $c=4.1042\left(3\right)\AA$. The resistivity and magnetic susceptibility measurements reveal that ThIrSn exhibits metallic behavior, low magnetoresistance, and paramagnetic characteristics. Hall effect measurements have determined that the carrier type is predominantly electrons, following a single-band model. Furthermore, first-principles calculations indicate that the electronic states near the Fermi level are predominantly contributed by Th and Ir. The band structure exhibits Dirac-like crossings and van Hove singularities at the $M$ and $K$ points, suggesting the potential existence of nontrivial topological characteristics. This work not only establishes ThIrSn as a promising platform for investigating potential topological metals, but also advances the study of ternary intermetallic compounds in distorted kagome lattice systems.

We study from ab initio density functional theory calculations the structural and magnetic properties of the crystal ${\mathrm{KCoF}}_3$. We found that the experimentally reported cubic to tetragonal phase transition is due to an electronic first-order Jahn-Teller effect from the $R$ zone boundary point. We also obtain that the magnetic ground state is the G-type antiferromagnetic order, in agreement with the $R$-point Jahn-Teller distortion and that the magnetic moment of the Co atoms contains a strong orbital contribution ($m_L=0.95 {\mu }_B$ in the cubic phase and 0.55 ${\mu }_B$ in the tetragonal phase). Furthermore, we compute the dynamical magnetic effective charges and show that it is zero by symmetry for the Co and they can reach a value as large as 200 ${10}^{-2}{\mu }_{\text{B}}/\text{Å}$ for the apical F anion. This large magnetic effective charge comes from the spin-orbit coupling (50% of the response is from the orbital moment) contrary to the rare-earth manganites and ferrites with similar order of magnitude but originating from the exchange striction mechanism. The fact that the dynamical magnetic effective charges are nonzero also proves that the tetragonal phase of ${\mathrm{KCoF}}_3$ is antimagnetoelectric with a large magnetic sublattice magnetoelectric response of 210 ps/m per spin channel. We also discuss the generality of these magnetic effective charges.

We investigate the impact of $\mathrm{O}{\mathrm{H}}^{-}$ ions incorporation on the lattice strain and spontaneous polarization of $\mathrm{BaTi}{\mathrm{O}}_3$ nanorods synthesized under different conditions. It was confirmed that the lattice strain depends directly on Ba supersaturation, with higher supersaturation leading to an increase in the lattice strain. However, it was shown that crystal growth and observed lattice distortion are not primarily influenced by external strain; rather, $\mathrm{O}{\mathrm{H}}^{-}$ ions incorporation plays a key role in generating internal chemical strains and driving these processes. By using the less reactive $\mathrm{Ti}{\mathrm{O}}_2$ precursor instead of $\mathrm{TiOC}{\mathrm{l}}_2$ and controlling Ba supersaturation, the slower nucleation rate enables more effective regulation of $\mathrm{O}{\mathrm{H}}^{-}$ ions incorporation and crystal growth. This in turn effects both particle size and lattice distortion, leading to $c/a$ ratio of 1.013–1.014. The incorporation of $\mathrm{O}{\mathrm{H}}^{-}$ ions induces lattice elongation along the $c$ axis, contributing to anisotropic growth, increasing of the rod diameter and their growth-induced bending. However, the possibility of the curvature-induced changes in domain morphology of $\mathrm{BaTi}{\mathrm{O}}_3$ nanorods remains almost unexplored. To study the possibility, we perform analytical calculations and finite element modeling, which provide insights into the curvature-induced changes in the strain-gradient, polarization distribution, and domain morphology in $\mathrm{BaTi}{\mathrm{O}}_3$ nanorods. Theoretical results reveal the appearance of the domain stripes in $\mathrm{BaTi}{\mathrm{O}}_3$ nanorod when the curvature exceeds a critical angle. The physical origin of the domain stripes emergence is the tendency to minimize the elastic energy of the nanorod by the domain splitting. These findings suggest that $\mathrm{BaTi}{\mathrm{O}}_3$ nanorods, with curvature-controllable amount of domain stripes, could serve as flexible race-track memory elements for flexotronics and domain-wall electronics. Overall, this work enhances the understanding of how the shape anisotropy, lattice strains, and strain gradients influence the domain morphology of ferroelectric nanorods, offering a pathway for tuning properties of the nanorods for advanced applications in nanoelectronics.

Elastic constants are central material properties, frequently reported in experimental and theoretical studies. While their computation is straightforward in the absence of thermal fluctuations, finite-temperature methods often suffer from poor signal-to-noise ratios, the presence of strong anharmonic effects, or require second-order derivatives with respect to spatial coordinates. Here, we show how to compute elastic constants in thermally ordered and disordered systems by generalizing a noise-cancellation method originally developed for piezoelectric coupling coefficients. A slight strain is applied to an equilibrated solid. Simulations of both the strained and unstrained (or oppositely strained) reference systems are performed using identical thermostatting schemes. As demonstrated theoretically and with generic one-dimensional models, this allows stress differences to be evaluated and elastic constants to be determined with favorable thermal noise. We then apply this approach across a diverse set of systems, spanning crystalline argon, ordered silicon, as well as amorphous silicon, poly(methyl methacrylate), and cellulose derivatives.

Surface oxides are associated with two-level systems (TLSs) that degrade the performance of niobium-based superconducting quantum computing devices. To address this, we introduce a predictive framework for selecting metal capping layers that inhibit niobium oxide formation. Using DFT-calculated oxygen interstitial and vacancy energies as thermodynamic descriptors, we train a logistic regression model on a limited set of experimental outcomes to successfully predict the likelihood of oxide formation beneath different capping materials. This approach identifies Zr, Hf, and Ta as effective diffusion barriers. Our analysis further reveals that the oxide formation energy per oxygen atom serves as an excellent standalone descriptor for predicting barrier performance. By combining this new descriptor with lattice mismatch as a secondary criterion to promote structurally coherent interfaces, we identify Zr, Ta, and Sc as especially promising candidates. This closed-loop strategy integrates first-principles theory, machine learning, and limited experimental data to enable rational design of next-generation materials.

Accessing metastable structural states in high-entropy alloys (HEAs) offers a promising route to tailor material properties, yet the use of high pressure to engineer such states remains underexplored. Here, we report the pressure-driven synthesis of a unique metastable dual-BCC microstructure in a near-equimolar ReNbTiZrHf alloy. Starting from an ambient two-phase mixture of hexagonal (C14-derived) and body-centered cubic (BCC) phases, compression induces a selective, diffusionless transformation of the hexagonal constituent into a second, crystallographically distinct BCC polymorph, while the original BCC phase remains stable. Upon decompression, the pressure-induced BCC phase is kinetically trapped, yielding a dual-BCC state that is inaccessible via conventional thermal processing. The pressure-stabilized BCC polymorph is Re-enriched and inherits the exceptional stiffness of its hexagonal parent (bulk modulus $\sim 290$ GPa), creating a composite microstructure with pronounced elastic and mechanical contrast relative to the softer original BCC matrix $(\sim 180 \mathrm{GPa})$. These findings demonstrate that pressure can effectively navigate the flat free-energy landscapes of chemically complex alloys, establishing a robust pathway for polymorph engineering and metastable phase design in refractory HEAs.

Er-doped ${\mathrm{Al}}_2{\mathrm{O}}_3$ is a promising host for telecom-band integrated photonics. Here we combine ab initio calculations with a symmetry-resolved analysis to elucidate substitutional Er on the Al site $\left({\mathrm{Er}}_{\mathrm{Al}}\right)$ in $\alpha \text{−}{\mathrm{Al}}_2{\mathrm{O}}_3$. First-principles relaxations confirm the structural stability of ${\mathrm{Er}}_{\mathrm{Al}}$. We then use the local trigonal crystal-field symmetry to classify the Er-derived impurity levels by irreducible representations and to derive polarization-resolved electric-dipole selection rules, explicitly identifying the symmetry-allowed $f-d$ hybridization channels. Kubo-Greenwood absorption spectra computed from Kohn-Sham states quantitatively corroborate these symmetry predictions. Furthermore, we connect the calculated intra-$4f$ line strengths to Judd-Ofelt theory, clarifying the role of $4f-5d$ admixture in enabling optical activity. Notably, we predict a characteristic absorption near 1.47 $\mu \mathrm{m}$ (telecom band), relevant for on-chip amplification and emission. To our knowledge, a symmetry-resolved first-principles treatment of Er:${\mathrm{Al}}_2{\mathrm{O}}_3$ with an explicit Judd-Ofelt interpretation has not been reported, providing a transferable framework for tailoring rare-earth dopants in wide-band-gap oxides for integrated photonics. Our results for the optical spectra are in good agreement with experimental data. The resulting symmetry-based selection rules translate directly to polarization-dependent coupling in ${\mathrm{Al}}_2{\mathrm{O}}_3$ integrated photonic waveguides and resonators, enabling device-level design of TE/TM-mode interaction with Er emitters in the 1.5-$\mu \mathrm{m}$ telecom band.

Compositional trends in III-V ternary nanowires grown by the vapor-liquid-solid method were extensively studied over the past decade. Conversely, the wurtzite-zincblende polytypism was investigated mainly for binary III-V nanowires. The crystal phase changes in III-V ternary nanowires and even the key parameters determining the preferred crystal structure of such nanowires remain largely unknown. Here, we try to fill the gap by presenting a model for the crystal phase in vapor-liquid-solid III-V ternary nanowires based on the surface energy analysis. Our approach is based on the known phase diagram of GaAs nanowires, and allows one to identify the crystal phase as a function of the droplet contact angle and composition. We show a qualitative trend agreement of the phase diagrams with the available experimental data on $\mathrm{I}{\mathrm{n}}_x\mathrm{G}{\mathrm{a}}_{1-x}\mathrm{As}, \mathrm{A}{\mathrm{l}}_x\mathrm{G}{\mathrm{a}}_{1-x}\mathrm{As}$, and $\mathrm{Ga}{\mathrm{P}}_x\mathrm{A}{\mathrm{s}}_{1-x}$ nanowires. We also discuss the general crystal phase trends and the remaining uncertainties that should be circumvented to enable the full description and compositional control of these complex growth systems.

We investigate the manipulation of weakly bound graphene nanoribbons (GNRs) on the Au(111) surface using large amplitude scanning force microscopy. The GNRs are fabricated in situ via surface-assisted Ullmann coupling. Mobile GNRs are identified in scanning images by increased noise due to their weak binding. Their mobility is reduced when they are part of an extended GNR network. Even during passive imaging, interactions between the tip and the GNR can induce slight movements, allowing us to approximate the corrugation of the surface binding potential. We demonstrate tip-induced rotation and lateral displacement of GNRs perpendicular to their axis, during which the ribbon is partially lifted from the surface. Based on first-principles calculations, we construct a two-dimensional potential energy landscape and perform climbing image nudged elastic band calculations to approximate energy barriers for translation. Both approaches show that the barrier strongly depends on the GNR orientation. In addition, we find that beyond a critical length, GNRs become effectively immobilized due to increased energy barriers and reduced flexibility. The theoretical results align well with the observed outcomes of the manipulation experiments.

Hydrogen uptake in brownmillerite perovskites ${\mathrm{A}}_2{\mathrm{B}}_2{\mathrm{O}}_5$ offers an (electro)chemically accessible route to tune functional properties, but mechanistic understanding and design rules for hydrogen-responsive oxides remain limited. Here, we employ density functional theory (DFT) to quantify how H absorption affects electronic structure, magnetic exchange, and anisotropy in representative ${\mathrm{Sr}}_2{\mathrm{Fe}}_2{\mathrm{O}}_5$ and ${\mathrm{Sr}}_2{\mathrm{Co}}_2{\mathrm{O}}_5$ oxides. We find that hydrogenation introduces a localized ${\mathrm{e}}^{-}$ that stabilizes near the ${\mathrm{H}}^{+}$, with B-site dependent preference. The resulting lattice distortions and redistribution of charge density modify exchange coupling and cant the Néel vector, giving rise to weak ferromagnetism. We also show that absorption energies are highly sensitive to ${\mathrm{H}}^{+}–{\mathrm{e}}^{-}$ arrangements and magnetic order, varying by up to 1 eV across different settings. This sensitivity demands consistent treatment of charge localization and spin states, together with careful choice of computational parameters. Extending to a variety of experimentally reported ${\mathrm{A}}_2{\mathrm{B}}_2{\mathrm{O}}_5$ compositions, we identify candidates with favorable H uptake and uncover a trend linking more favorable absorption to a higher B-site $d$-electron count. We also demonstrate that the preferential ${\mathrm{H}}^{+}$ absorption site in these materials is governed by local O–O separations and lattice flexibility, which describe the ability of the framework to accommodate ${\mathrm{H}}^{+}$-induced distortions. Finally, benchmarks of universal machine-learning interatomic potentials reveal uncertainties of about 1 eV for site-resolved absorption energies, motivating descriptor-based surrogate models and targeted DFT validation. Together, these results establish practical design rules for hydrogen-responsive oxides relevant to iono-electronic devices, sensors, and electrically tunable spin functionality.

Understanding the mechanisms of helium-induced damage in zirconium alloys used in nuclear reactors is essential for ensuring both reactor safety and the longevity of materials. However, atomistic simulation of helium (He) in $\alpha$ -zirconium ( $\alpha$ -Zr) has proven to be challenging due to the limitations of conventional empirical potentials. In this study, we developed a deep-potential (DP) model to explore the diffusion and nucleation behavior of He in $\alpha$ -Zr through molecular dynamics simulations. The DP model demonstrates strong consistency with density functional theory (DFT) results in predicting elastic constants, phonon spectra, and thermodynamic properties, significantly outperforming traditional empirical potentials. We found that helium atoms preferentially occupy the basal octahedral (BO) and tetrahedral (T) interstitial sites in $\alpha$ -Zr, with a diffusion activation energy of 0.34 eV. Increased concentrations of He in $\alpha$ -Zr lead to lattice distortions, which degrade the material's mechanical properties. The process of He bubble aggregation shows characteristics of dynamic equilibrium, and the size of the He clusters in $\alpha$ -Zr is positively correlated with temperature.

We demonstrate precise control of magnetism in ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ thin films through careful synthesis by molecular beam epitaxy, achieving minimal defects and accurate layer thickness control. By optimizing Mn-Bi-Te ratios and growth temperatures, we minimize detrimental self-doping effects and accurately target integer-layer films. X-ray diffraction and reflectivity provide quantitative measures of film quality and thickness. When these macroscale probes of structure and thickness are integrated with magnetotransport measurements, a striking even-odd layer dependence of the anomalous Hall effect is revealed. Odd-layer films exhibit a large hysteresis up to the Néel temperature ($\sim 25\mathrm{K}$), consistent with noncompensated antiferromagnetism, while even-layer films show minimal response, as expected for an antiferromagnet. The sign of the anomalous Hall effect exhibits a sign reversal for intrinsic magnetism versus magnetism associated with defects. This work identifies critical factors for inducing pure, noncompensated ferromagnetism and reveals the characteristics of the intrinsic anomalous Hall effect in ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$, which together is a step toward realizing the zero-field quantum anomalous Hall effect in topological materials.