Hexagonal ${\mathrm{TbInO}}_3$ exhibits spin liquid behavior at low temperatures and improper ferroelectricity at room temperature, and as such may host novel electronic and magnetic states upon carrier doping. This paper presents density functional theory (DFT) calculations of the electronic, dielectric, and defect properties of ${\mathrm{TbInO}}_3$. We study ${\mathrm{Ti}}^{4+}$ and ${\mathrm{Ca}}^{2+}$ as substitutional dopants replacing ${\mathrm{In}}^{3+}$ and ${\mathrm{Tb}}^{3+}$ to introduce electron- and hole-doping, respectively. Point defect calculations reveal that ${\mathrm{Ti}}^{4+}$ dopants introduce shallow defect states near the conduction band minimum, suggesting the possibility of $n$-type conductivity, whereas ${\mathrm{Ca}}^{2+}$ dopants result in deep in-gap states. We also analyze changes to structural properties with relatively large (8%–16%) Ca and Ti concentrations. We utilize molecular beam epitaxy (MBE) to synthesize epitaxial thin films of ${\mathrm{TbInO}}_3$ doped with ${\mathrm{Ti}}^{4+}$ and ${\mathrm{Ca}}^{2+}$, and use scanning transmission electron microscopy (STEM) imaging to show that the experimental films corroborate the doping-induced structural changes found with DFT. However, all samples remain electrically insulating, which we attribute to the localization of added carriers on the Tb cation. Finally, we propose charge-transfer doping as an alternative strategy to induce conductivity in ${\mathrm{TbInO}}_3$, and identify several possible substrates to achieve this.

The two-dimensional magnetic triangular lattice, with rare-earth local moments coupled through long-range interactions and hosting strong spin-orbit coupling, serves as an ideal platform for exploring novel quantum phenomena. Here, we report the physical properties of ${\mathrm{DyNiAl}}_4{\mathrm{Ge}}_2$ single crystals through comprehensive structural, magnetic, heat capacity, electrical transport, and neutron powder diffraction measurements. ${\mathrm{DyNiAl}}_4{\mathrm{Ge}}_2$ crystallizes in a trigonal lattice with the space group $R\overline{3}m$, where Dy atoms form two-dimensional triangular lattice layers within the $\mathit{ab}$ plane and stack along the $c$ axis. Magnetic susceptibility measurement reveals a magnetic phase transition at $T_N$ = 9.0 K, further confirmed by the $\lambda$-shaped peak in the heat capacity curve. The obtained temperature-magnetic field phase diagram is relatively simple compared to other isostructural compounds, suggesting the absence of magnetic frustration. This is further evidenced by neutron powder diffraction, which shows a collinear antiferromagnetic ground state with a propagation vector $\mathit{k}$ = (0, 0, 1.5), implying the absence of magnetic frustration in ${\mathrm{DyNiAl}}_4{\mathrm{Ge}}_2$. In this magnetic structure, Dy moments are aligned ferromagnetically within each triangular layer and arranged antiferromagnetically between adjacent layers along the $c$ axis. Our results establish ${\mathrm{DyNiAl}}_4{\mathrm{Ge}}_2$ as a model system for understanding the interplay between RKKY interaction and geometrical frustration in this family of compounds.

Geometrically frustrated spin systems continue to serve as a fertile ground for realizing nontrivial quantum states, making the exploration of new materials in this category a central pursuit. In this work, we report the synthesis and investigation of a new family of antiferromagnets, $\mathrm{LiBa}{\mathrm{RE}}_2{\left(\mathrm{B}{\mathrm{O}}_3\right)}_3$ (RE = Pr, Nd, Sm–Tb). These compounds crystallize in the trigonal $P\overline{3}m1$ space group, where neighboring $\mathrm{RE}{\mathrm{O}}_9$ polyhedra share faces to form spatially confined ${\mathrm{RE}}_6$ spin hexamers. These hexamers interconnect within the $ab$ plane to construct a two-dimensional frustrated triangular spin-hexamer lattice, featuring hierarchical spin interactions with strong intracluster and weak intercluster couplings. Magnetic susceptibility measurements down to 1.8 K reveal no signs of long-range magnetic order or spin freezing across the entire series, despite the presence of dominant antiferromagnetic interactions. Further magnetization studies on a representative member $\mathrm{LiBaG}{\mathrm{d}}_2{\left(\mathrm{B}{\mathrm{O}}_3\right)}_3$ down to 0.4 K uncover a long-range antiferromagnetic transition at ∼0.91 K. Quasi-adiabatic demagnetization experiments on this material demonstrate outstanding cooling effect, reaching a pronounced temperature minimum at ∼146 mK near the antiferromagnetic critical field ${\mu }_0{H}_c\sim 0.75$ T. Notably, this temperature valley is markedly broadened over an extended field interval, indicating the presence of a quantum critical state near ${\mu }_0{H}_c$ with persistent spin fluctuations. Altogether, $\mathrm{LiBa}{\mathrm{RE}}_2{\left(\mathrm{B}{\mathrm{O}}_3\right)}_3$ represents a versatile platform of frustrated spin clusters, offering new possibilities for exploring unconventional magnetic ground states and potential cryogenic cooling applications.

We investigate the structural and electronic conditions conducive to superconductivity in layered nickelates using density-functional theory. For both the bilayer and 1–3 polymorphs of ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$, we find that the in-plane Ni–O–Ni bond angles under pressure strongly correlate with the experimentally observed superconducting transition temperature ($T_c$) dome, and may serve as a reasonable proxy. Under compressive strain, the bond angles straighten, peaking near 2% strain, consistent with experimental reports of superconductivity in strained bilayer thin films. However, the bond angles at this strain are more bent than those achieved under hydrostatic pressure, correlating with a lower $T_c$. We show that increasing the number of ${\mathrm{NiO}}_2$ layers, as in ${\mathrm{La}}_4{\mathrm{Ni}}_3{\mathrm{O}}_{10}$, or substituting heavier rare-earth elements (e.g., Pr), raises the pressure required to reach the structural configuration associated with superconductivity. Our results indicate that these systems require higher external pressure to achieve in-plane bond straightening. Varying the on-site Coulomb interaction $U$ reveals that stronger electronic correlations delay the structural transition and favor high-spin states. This suggests that moderate correlation strength may be optimal for superconductivity, with stronger correlation preventing the formation of favorable bond geometries. Electronic structure analysis shows that the Ni $e_g$ orbitals dominate near the Fermi level and shift downward with pressure, enhancing Ni–O hybridization. These results highlight how pressure and strain tune structural features that may be essential for engineering high-$T_c$ phases in nickelate superconductors.

Efficient and safe energy storage technologies are essential for realizing a sustainable and electrified society. Among the key challenges, the design of superionic conductors for all-solid-state batteries often faces a fundamental tradeoff between stability and ionic conductivity. Random substitutional crystals, where atomic species are randomly distributed throughout a crystal lattice, present a promising route to overcome this tradeoff. Although the importance of cooperative motion in ion conduction has been pointed out, there is a lack of understanding of the relationship between mesoscale structural organization and macroscopic conductivity, limiting the rational design of optimal compositions. Here, we systematically investigate the ionic conductivity of rocksalt random substitutional ionic crystals ${\mathrm{Li}}_x{\mathrm{Pb}}_{1-2x}{\mathrm{Bi}}_x\mathrm{Te}$ as a function of Li concentration $x$ using molecular dynamics simulations. We find that ionic conductivity increases sharply once the $x$ exceeds a critical threshold, without disrupting the underlying crystal structure. Strikingly, this threshold aligns with the site-percolation threshold predicted by percolation theory. Our findings establish ion percolation as a universal design principle that reconciles the tradeoff between conductivity and stability, offering a simple and broadly applicable strategy for the development of robust, high-performance solid electrolytes.

Molecular dynamics simulations can provide structural information of glass materials with atomic resolution and for very short time scales. In turn, this requires accurate and effective force fields. Here, focusing on alkali silicate glasses, we develop transferable force fields that are applicable across a wide range of temperatures and compositions. Using on-the-fly machine learning routines, these force fields produce energy and force predictions with accuracy comparable to that of density functional theory. The potential energy landscape is described using structural descriptors that incorporate both radial and angular information within a reduced-dimensional descriptor space. We then employ these accurate machine learning force fields (MLFFs) to prepare silica and binary alkali $({\mathrm{Li}}_2\mathrm{O},$ ${\mathrm{Na}}_2\mathrm{O},$ ${\mathrm{K}}_2\mathrm{O})$ silicate glass samples, allowing us to study their structures. We assess the composition dependence of the structural characteristics of the glasses by computing several key parameters, including neutron structure factor, pair distribution function, angular distribution function, coordination number, and $Q^n$ speciation. The trained MLFFs accurately reproduce the splitting of the first sharp diffraction peak in potassium silicate glasses, consistent with experimental findings, and reveal that its structural origin is tied to Si-K interactions. Overall, our research demonstrates the power of combining advanced computational techniques with classical structural analysis methods to enhance our structural understanding of complex glass systems.

Achieving atomic-level understanding of crystallization of molten salts is of importance to a wide range of technological applications. Recent work [Fan et al., Proc. Natl. Acad. Sci. USA 122, e2425702122 (2025)] revealed that crystal nucleation in molten LiF salt is a multistage process according to the molecular-dynamics (MD) simulations based on an atomic cluster expansion (ACE) machine-learning interatomic potential (MLIP). In order to understand the influence of increasing cation size on nucleation pathways and nucleation rates of molten fluoride salts, here we develop two new ACE MLIPs for NaF and KF. The two ACE MLIPs feature DFT-SCAN-level accuracy for liquid and multiple solid polymorphs over a wide temperature (0–2000 K) and pressure (0–100 GPa) range, and also reproduce well a number of experimental data for solid and liquid equilibrium properties. The efficiency of the two ACE MLIPs enable million-atom-scale or microsecond-scale MD simulations. The two general-purpose ACE MLIPs are expected to be useful for atomistic simulations for different purposes, in addition to studying crystallization of molten NaF and KF salts.

The exploration for novel two-dimensional (2D) monolayers with diverse electronic characteristics has attracted growing interest in recent years. Using density functional theory (DFT) calculations, we have predicted a new family of 2D transition-metal- (TM) based compounds under the nomenclature ${\mathrm{M}}_2{\mathrm{X}}_2$ (where M represents TMs and X denotes chalcogen elements like S, Se, and Te). Our investigation delves into the examination of the formation energies, dynamical or thermal stabilities, mechanical properties, electronic structures, and magnetic properties of various systems within this family. Through our computational analyses, we have discovered a total of 35 thermodynamically and dynamically stable ${\mathrm{M}}_2{\mathrm{X}}_2$ monolayer materials that exhibit remarkable diversity in terms of their electronic and magnetic properties. Our findings will pave the way for the experimental realization of various ${\mathrm{M}}_2{\mathrm{X}}_2$ structures in the near future. In particular, among the predicted compounds, ${\mathrm{M}}_2{\mathrm{X}}_2$ $(\mathrm{M}=\mathrm{Zn}, \mathrm{Cd}\text{;} \mathrm{X}=\mathrm{S}, \mathrm{Se}, \mathrm{Te})$ are a direct band-gap semiconductor with band gaps between 0.9 to 2.6 eV (1.3 to 3.7 eV) by DFT+Perdew-Burke-Ernzerhof (hybrid functional HSE) calculations. ${\mathrm{M}}_2{\mathrm{X}}_2$ $(\mathrm{M}=\mathrm{Ti}, \mathrm{Zr}, \mathrm{Hf}, \mathrm{Tc}, \mathrm{Re})$ are zero-gap semiconductor (semimetals) in standard $\mathrm{DFT}+\mathrm{PBE}$ calculation. Inclusion of spin-orbit coupling leads to a gap opening of 0.1 eV. Notably, our analysis has also unveiled the magnetic nature of certain materials, such as ${\mathrm{Mn}}_2{\mathrm{X}}_2$ $(\mathrm{X}=\mathrm{S}, \mathrm{Se})$, ${\mathrm{Fe}}_2{\mathrm{X}}_2$ $(\mathrm{X}=\mathrm{Se}, \mathrm{Te})$, and ${\mathrm{Ti}}_2{\mathrm{Te}}_2$. The prediction of semiconducting (magnetic) ${\mathrm{M}}_2{\mathrm{X}}_2$ materials not only offers valuable insights into the underlying electronic properties (magnetism) of 2D systems but also positions these materials as promising candidates for the development of advanced electronic (spintronic) devices.

We investigate the Sn-substitution effect on the thermoelectric transport properties of the layered cobaltite ${\left[{\mathrm{Ca}}_2{\mathrm{CoO}}_3\right]}_{0.62}\left[{\mathrm{CoO}}_2\right]$ single crystals, which exhibit a nonmonotonic temperature variation of the electrical resistivity and the Seebeck coefficient owing to the complex electronic and magnetic states. We find that the onset temperature of the short-range spin-density-wave (SDW) formation increases with the substituted Sn content, indicating the impurity-induced stabilization of the SDW order, reminiscent of the disorder/impurity-induced spin order in the cuprate superconductors. The Seebeck coefficient is well related to such impurity effects, as it is slightly enhanced below the onset temperatures, implying a decrease in the carrier concentration due to a pseudogap formation associated with the SDW ordering. We discuss the site-dependent substitution effects including earlier studies, and suggest that substitution to the conducting ${\mathrm{CoO}}_2$ layers is essential to increase the onset temperature, consistent with the impurity-induced SDW picture realized in the conducting layers with the cylindrical Fermi surface.

The mechanical loss angle of amorphous ${\mathrm{TiO}}_2$-doped ${\mathrm{GeO}}_2$ can be lower than ${10}^{-4}$, making it a candidate for Laser Interferometer Gravitational-wave Observatory (LIGO) mirror coatings. Amorphous oxides have complex atomic structures that are influenced by various factors, including doping concentration, preparation, and thermal history, resulting in different mass densities and physical properties. Modeling at the atomistic level enables capturing these effects by generating atomic structure models according to experimental conditions. In order to obtain reliable and physical amorphous models at an affordable cost, we develop classical and machine-learning potentials (MLP) to speed up simulations. First-principles calculations are used to train and validate MLP as well as to validate structure models. To better reproduce properties such as elastic modulus, radial distribution function (RDF), and the variations in mass density of doped amorphous oxides, density functional theory (DFT) calculations are used to optimize the final models. We find that the mass densities of amorphous systems are correlated with the total void volume. The experimental mass density matches the models with the most symmetric potential energy wells under volume change. The elastic response of the metal-oxygen network is also studied. The 27% ${\mathrm{TiO}}_2$ doped ${\mathrm{GeO}}_2$ system shows the least number of large atom-atom distance changes, while for 44% ${\mathrm{TiO}}_2$ doped ${\mathrm{GeO}}_2$, a majority of Ti-O distances are significantly changed. In response to strains, the metal-oxygen network at low mass densities prefers to adjust bond angles, while at high mass densities, the adjustment is mainly done by changing atom-atom distance.

We have investigated the electronic structure of ${\mathrm{Ba}}_3{\mathrm{InIr}}_2{\mathrm{O}}_9$ within the density-functional theory using the generalized gradient approximation while considering strong Coulomb correlations ($\mathrm{GGA}+U$) in the framework of the fully relativistic spin-polarized Dirac linear muffin-tin orbital band-structure method. We have studied resonant inelastic x-ray scattering (RIXS) spectra of ${\mathrm{Ba}}_3{\mathrm{InIr}}_2{\mathrm{O}}_9$ at the Ir $L_3$ edge for the monoclinic $C2/c$ and hexagonal $P{6}_3/mmc$ crystal structures. The calculated results are in good agreement with experimental data. The RIXS spectrum at the Ir $L_3$ edge possesses several sharp features below 2 eV, corresponding to transitions within the Ir $t_{2g}$ levels. The excitation located from 2 to 5 eV is due to $t_{2g} \to e_g$ transitions. The wide structure situated at $5-12\mathrm{eV}$ appears due to charge transfer transitions. The influence of the momentum transfer vector and incident photon energy on the Ir $L_3$ RIXS spectrum has been investigated. Also, we have calculated the RIXS spectra of ${\mathrm{Ba}}_3{\mathrm{InIr}}_2{\mathrm{O}}_9$ at the Ir $K, M_3, M_5, N_3, N_5$, and $N_7$ edges to study the influence of core states on the resulting Ir RIXS spectra. The theoretical RIXS spectrum at the oxygen $K$ edge has also been analyzed.

${\mathrm{Sr}}_2{\mathrm{FeO}}_{4-\delta }$ is a first-order Ruddlesden-Popper perovsike-type material, prospective as a positrode (O-electrode) material for solid oxide and protonic ceramic electrochemical cells. By means of $\mathrm{DFT}+U_{\mathrm{eff}}$, oxygen vacancies (${\mathrm{V}}_{\mathrm{O}}^{••}$) and interstitials (${\mathrm{O}}_i^{{}^{″}}$) have been modelled in a broad oxygen stoichiometry range of $\delta =0.125$ to 0.5. For each δ value, all symmetry inequivalent configurations were identified, yielding the ${\mathrm{V}}_{\mathrm{O}}^{••}$ formation energy in the range of 2.0–2.4 eV, almost independent of δ (unlike for simple perovskites). We assign the individual Fe charge states in ${\mathrm{Sr}}_2{\mathrm{FeO}}_{4-\delta }$ (“oxidation state map”) based on magnetic moment and average Fe-O distance. Interestingly, ${\mathrm{V}}_{\mathrm{O}}^{••}$ and $\mathrm{F}{\mathrm{e}}^{3+}$ energetically prefer not to be nearest neighbors. Regarding oxygen interstitial species, a $\mathrm{Sr}\text{−}{\mathrm{O}}_2^{2-}\text{−}\mathrm{Fe}$ defect is the most stable form. Oxygen interstitial transport mechanism occurs predominantly within the SrO layer with the intermediate formation of a single oxide ${\mathrm{O}}_i^{2-}$ and an average barrier of 0.5 eV. Oxygen vacancy migration is preferred along a zig-zag path within the $\mathrm{Fe}{\mathrm{O}}_2$ layer with an effective barrier of 0.6 eV. The comprehensive analysis of ${\mathrm{Sr}}_2{\mathrm{FeO}}_{4-\delta }$—serving as prototype also for higher Ruddlesden-Popper phases—including oxidation state map and oxygen defect migration, paves the way for coming investigations of the protonated materials.

The dissolution behavior of tungsten carbide (WC) particles in liquid cobalt is investigated using ab initio and classical molecular-dynamics calculations. It turns out that at the atomic level there is a complex interplay between surface properties, bulk diffusion, and dissolution. It is found that carbon-rich shells form around dissolving WC particles, creating a semidissolved state. The dissolution process is decelerated by trapping carbon atoms via the formation of carbon-carbon bonds, both on the surface of dissolving particles and in the surrounding semidissolved shell. Upon reaching a critical particle radius, the dissolution rate sharply increases, driven by changes in the number of carbon-carbon bonds, resulting in a premelting behavior. The existence of a semidissolved shell and premelting behavior advance our understanding of dissolution mechanisms at the atomic scale and can be applicable for controlling dissolution processes that are an important part of coarsening of WC particles, a phenomenon taking place during cemented carbide manufacturing.

Phase-field models accurately simulate microstructure evolution, but their dependence on solving complex differential equations makes them computationally expensive. This work achieves a significant acceleration via a deep learning-based framework, utilizing a conditional variational autoencoder (CVAE) coupled with cubic spline interpolation and spherical linear interpolation (SLERP). We demonstrate the method for binary spinodal decomposition by predicting microstructure evolution for intermediate alloy compositions from a limited set of training compositions. First, using microstructures from phase-field simulations of binary spinodal decomposition, we train the CVAE, which learns compact latent representations that encode essential morphological features. Next, we use cubic spline interpolation in the latent space to predict microstructures for any unknown composition. Finally, SLERP ensures smooth morphological evolution with time that closely resembles coarsening. The predicted microstructures exhibit high visual and statistical similarity to phase-field simulations. This framework offers a scalable and efficient surrogate model for microstructure evolution, enabling accelerated materials design and composition optimization.

Excitons form in semiconductors and govern light-matter interaction, while for metals, the Coulomb interaction is strongly screened and the dominant excitations are plasmons. Here we assemble all-metal nanowires using icosahedral $M@X_{12}$ ($M$ = group VB and VIB elements; $X$ = Au, Ag, Cu) superatomic clusters, which are accessible in the laboratory. They exhibit strong excitonic effects featuring large binding energies and high energy-momentum dispersions of excitons, along with strong optical responses in the mid- and far-infrared regions. Moreover, the nanowires assembled by $\mathrm{Nb}@\mathrm{A}{\mathrm{u}}_{12}$ and $\mathrm{Ta}@\mathrm{A}{\mathrm{u}}_{12}$ clusters have quasiparticle gaps below 1 eV, exhibiting excitonic instability to the formation of an excitonic insulator. These one-dimensional superatomic crystals present a paradigm for exploring new exciton physics toward practical device implementations.