Structural, electronic, and thermodynamic properties of native defects in GaS and GaSe monolayers are investigated by means of accurate ab initio calculations. Based on their charge transition levels we assess the influence of the studied defects on the electrical properties of the monolayers. Specifically, we show that native defects do not behave as shallow dopants and their presence cannot account for the experimentally observed intrinsic doping. In addition, we predict that native defects are efficient compensation and recombination centers. Besides pointing out their detrimental nature, we also calculate the corresponding finite-temperature formation energies and provide a window of growth conditions able to reduce the concentration of all relevant native defects.

Two-dimensional materials have great potential for applications as high-performance electronic devices and efficient thermal rectificators. Among them, pristine phosphorene, a single layer of black phosphorus, has shown promising properties such as ultrahigh charge mobility, a tunable band gap, and mechanical flexibility. However, the introduction of extended structural defects such as grain boundaries (GBs) has, in general, a detrimental influence on the electronic and thermal transport properties by causing additional scattering events. In this computational study, based on a combination of a density-functional parametrized tight-binding approach with the Landauer theory of quantum transport, we show that applying a strain can help to partially counteract this effect. We exemplify this by addressing the electronic and phononic transmission of two specific grain boundaries containing $5|7$ (GB1) and $4|8$ (GB2) defects, respectively. Under uniaxial strain, the electronic band gaps can be reduced for both types of GB, while the respective thermal conductance is only weakly affected despite rather strong changes in the frequency-resolved phonon transmission. The combination of both effects mainly produces an increase of about a factor of 2 in the thermoelectric figure of merit $ZT$ for a GB2 system. Hence, our results provide insights into the manipulation of transport properties as well as the generation of potential thermoelectric materials based on phosphorene.

The magnetic properties of the $S=1/2$ two-dimensional square-lattice antiferromagnets ${\mathrm{Sr}}_2{\mathrm{NiO}}_{3}X$ $(X=\mathrm{Cl}, \mathrm{F})$ with the trivalent nickel ions in a low-spin state were studied by magnetic susceptibility, heat capacity, neutron powder diffraction, high-field electron spin resonance (ESR), muon spin rotation and relaxation $\left({\mu }^{+}\mathrm{SR}\right)$ measurements, and density functional theory (DFT) calculations. Both oxyhalides are isostructural to an ideal quantum square-lattice antiferromagnet ${\mathrm{Sr}}_2{\mathrm{CuO}}_2{\mathrm{Cl}}_2$, but the chlorine/fluorine anion exclusively occupies an apical site in an ordered/disordered manner with an oxygen anion, resulting in the formation of highly distorted ${\mathrm{NiO}}_{5}X$ octahedra with an off-center nickel ion. Magnetic susceptibility measurements revealed a remarkable difference between these two compounds: the magnetic susceptibility of ${\mathrm{Sr}}_2{\mathrm{NiO}}_3\mathrm{Cl}$ exhibited a broad maximum at approximately 35 K, which is typical of low-dimensional antiferromagnetic behavior. In contrast, the magnetic susceptibility of ${\mathrm{Sr}}_2{\mathrm{NiO}}_3\mathrm{F}$ exhibited spin-glass-like behavior below 12 K. No anomaly associated with long-range magnetic ordering was observed in the heat capacity, ESR, and neutron powder diffraction experiments. However, ${\mu }^{+}\mathrm{SR}$ measurements revealed the emergence of a static magnetic ordered state below $T_{\mathrm{N}}=28\mathrm{K}$ in ${\mathrm{Sr}}_2{\mathrm{NiO}}_3\mathrm{Cl}$ and a short-range magnetic state below $T_{\mathrm{N}}=18\mathrm{K}$ in ${\mathrm{Sr}}_2{\mathrm{NiO}}_3\mathrm{F}$. The DFT calculations suggested that the unpaired electron occupied a $d_{3z^2-r^2}$ orbital, and ferromagnetic couplings between the nearest-neighbor nickel spins were energetically favored. The mechanism of ferromagnetic superexchange interactions and the reason for the difference between the magnetic ground states in these nickel oxyhalides are discussed.

In this paper, a machine-learning-based method is proposed for predicting the x-ray absorption near-edge structure (XANES) for local configurations specific to amorphous materials. A combination of molecular dynamics and first-principles XANES simulations was adopted. The XANES spectrum was assumed to be accurately represented by linear regression of the local atomic descriptors. A comprehensive prediction of Si $K$-edge XANES spectra was performed based on an atom-centered symmetry function, smooth overlap of atomic positions, local many-body tensor representation, and spectral neighbor analysis potential. Furthermore, prediction accuracy was improved by compression of XANES spectral data and efficient sampling of training data.

Magnetic dilution of a well-established Kitaev candidate system is realized in the substitutional ${\mathrm{Ru}}_{1-x}{\mathrm{Rh}}_x{\mathrm{Cl}}_3$ series $(x=0.02–0.6)$. Optimized syntheses protocols yield uniformly doped single crystals and polycrystalline powders that are isostructural to the parental $\alpha \text{−}{\mathrm{RuCl}}_3$ as per x-ray diffraction. The Rh content $x$ is accurately determined by the quantitative energy-dispersive x-ray spectroscopy technique with standards. We determine the magnetic phase diagram of ${\mathrm{Ru}}_{1-x}{\mathrm{Rh}}_x{\mathrm{Cl}}_3$ for in-plane magnetic fields from magnetization and specific-heat measurements as a function of $x$ and stacking periodicity and identify the suppression of the magnetic order at $x\approx 0.2$ towards a disordered phase, which does not show any clear signature of freezing into a spin glass. Comparing with previous studies on the substitution series ${\mathrm{Ru}}_{1-x}{\mathrm{Ir}}_x{\mathrm{Cl}}_3$, we propose that chemical pressure would contribute to the suppression of magnetic order, especially in ${\mathrm{Ru}}_{1-x}{\mathrm{Ir}}_x{\mathrm{Cl}}_3$, and that the zigzag magnetic ground state appears to be relatively robust with respect to the dilution of the Kitaev-$\mathrm{\Gamma }$-Heisenberg magnetic lattice. We also discovered a slight dependence of the magnetic properties on thermal cycling, which would be due to an incomplete structural transition.

The electronic transport properties of a highly hydrogen-substituted 1111-type SmFeAsO epitaxial film with high critical-temperature $(T_{\mathrm{c}}=45\mathrm{K})$ were investigated under high magnetic fields. By using a single-turn magnet generating up to 130 T, we clarified that the upper critical field $\left({\mu }_0{H}_{\mathrm{c}2}\right)$ of $\mathrm{SmFeAs}{\mathrm{O}}_{0.65}{\mathrm{H}}_{0.35}$ is 120 T at the nearly low-temperature limit of 2.2 K for ${\mu }_{0}H\parallel ab$. The angular dependence of ${\mu }_0{H}_{\mathrm{c}2}$ revealed that the anisotropic parameter $\left(\gamma \right)$ around $T_{\mathrm{c}}$ is $\sim 2$, which is comparable with that of a practical candidate 122-type $\mathrm{Ba}{\mathrm{Fe}}_2{\mathrm{As}}_2$ with lower $T_{\mathrm{c}}$ and much smaller than that of F-substituted SmFeAsO. The small $\gamma$ mainly originates from the high hydrogen incorporation. The extremely high ${\mu }_0{H}_{\mathrm{c}2}$ and small $\gamma$, together with the high $T_{\mathrm{c}}$ and high critical current density, suggest that $\mathrm{SmFeAs}{\mathrm{O}}_{1-x}{\mathrm{H}}_x$ has high potential for the superconducting electromagnets and cables.

Thin garnet films are becoming central for magnon-spintronics and spin-orbitronics devices as they show versatile magnetic properties together with low magnetic losses. These fields would benefit from materials in which heat does not affect the magnetization dynamics, an effect known as the nonlinear thermal frequency shift. In this study, low-damping Bi substituted iron garnet (Bi:YIG) ultrathin films have been grown using pulsed laser deposition. Through a fine-tuning of the growth parameters, the precise control of the perpendicular magnetic anisotropy allows to achieve a full compensation of the dipolar magnetic anisotropy. Strikingly, once the growth conditions are optimized, varying the growth temperature from ${405}^{\circ }\mathrm{C}$ to ${475}^{\circ }\mathrm{C}$ as the only tuning parameter induces the easy axis to go from out of plane to in plane. For films that are close to the dipolar compensation, ferromagnetic resonance measurements yield an effective magnetization ${\mu }_0{M}_{\mathrm{eff}}\left(\mathrm{T}\right)$ that has almost no temperature dependence over a large temperature range (260 to 400 K) resulting in an anisotropy temperature exponent of 2. These findings put the Bi:YIG system among the very few materials in which the temperature dependence of the magnetic anisotropy varies at the same rate as the saturation magnetization. This interesting behavior is ascribed phenomenologically to the sizable orbital moment of ${\mathrm{Bi}}^{3+}$.

An atomistic effective Hamiltonian is used to study the response of a $(\mathrm{Bi},\mathrm{Nd}){\mathrm{FeO}}_3$ (BNFO) solid solution to a train of THz electric field pulses. Several hidden states (i.e., states that are usually not thermodynamically accessible) with various magnitudes of the electric polarization as well as different oxygen octahedral tilting patterns and antipolar arrangements are found, which is promising for designing ultrafast neuromorprhic architectures. The occurrence of these hidden states, along with the accompanying polarization pumping, originates from the specific trilinear and biquadratic couplings between oxygen octahedral tiltings and cation displacements. Consequently, the THz-activated transformation between these different states can be thought to be a ratchet mechanism both in real and reciprocal spaces.

Bulk ${\mathrm{EuPd}}_2{\mathrm{Si}}_2$ show a temperature-driven valence transition of europium from $\sim +2$ above 200 K to $\sim +3$ below 100 K, which is correlated with a shrinking by approximately 2% of the tetragonal crystal lattice along the two $a$-axes. Due to this interconnection between lattice and electronic degrees of freedom the influence of strain in epitaxial thin films is particularly interesting. Ambient x-ray diffraction (XRD) confirms an epitaxial relationship of tetragonal ${\mathrm{EuPd}}_2{\mathrm{Si}}_2$ on MgO(001) with an out-of plane $c$-axis orientation for the thin film, whereby the $a$-axes of both lattices align. XRD at low temperatures reveals a strong coupling of the thin film lattice to the substrate, showing no abrupt compression over the temperature range from 300 to 10 K. Hard x-ray photoelectron spectroscopy at 300 and 20 K reveals a temperature-independent valence of $+2.0$ for Eu. The evolving biaxial tensile strain upon cooling is suggested to suppress the valence transition. Instead temperature-dependent transport measurements of the resistivity and the Hall effect in a magnetic field up to 5 T point to a film thickness independent phase transition at 16 to 20 K, indicating magnetic ordering.

Significant efforts developing ${\mathrm{MoS}}_2\text{−}\mathrm{PbS}$-based heterostructure devices with several different architectures show promise for photosensor, solar cell, and chemical sensor applications. Merelaniite $\left({\mathrm{Mo}}_4{\mathrm{Pb}}_4{\mathrm{VSbS}}_{15}\right)$ is a newly discovered natural van der Waals heterostructure of the cylindrite type, composed predominantly of heavily modulated pseudotetragonal PbS layers and pseudohexagonal ${\mathrm{MoS}}_2$ layers with large misfit-induced anisotropy. For an incommensurate modulated structure, the refined structural model from single-crystal x-ray diffraction analysis is in reasonable agreement with the results obtained by high-resolution scanning transmission electron microscopy, especially in light of the fact that that the two isolated single-crystal domains used for the x-ray and electron diffraction experiments were extracted from two different whiskers and subjected to different sample preparation methods. The effects of the misfit-induced structural anisotropy are studied using angle-resolved polarized Raman spectroscopy. The intensities of 12 Raman modes are studied as a function of incident polarization angle relative to merelaniite's whisker axis, and show maximal intensity with the polarization direction perpendicular to the whisker axis. Polarization-dependent anisotropic third-harmonic generation from ultrathin mechanically exfoliated flakes reveals the anisotropy of the third-order nonlinear susceptibility tensor. Merelaniite demonstrates an expanded structure-chemistry space for engineering stable layered materials for potential device applications.

We report the dielectric properties of a two-dimensional layered Ruddlesden-Popper halide perovskite ${\mathrm{Cs}}_2{\mathrm{PbI}}_2{\mathrm{Cl}}_2$ synthesized via a simple mechanochemical process to explore fundamental aspects of ionic conduction and relaxation mechanism over a wide temperature and frequency range. Several experimental techniques, such as complex impedance spectroscopy, alternating current (AC) conductivity spectroscopy, and complex electric modulus spectroscopy, have been employed to investigate the nuances of ionic conduction and relaxation mechanisms, and the results have been corroborated using different theoretical models, such as the Maxwell-Wagner equivalent circuit model, the modified Jonscher power law, the Havrilliak-Negami (HN), and the Kohlrausch-Williams-Watts (KWW) model. The contribution of the grains and grain boundaries to the total impedance in the system is estimated by the analysis of the Nyquist plots. In temperature-dependent AC conductivity spectra, a critical temperature (413 K) is observed, beyond which the conductivity increases abruptly. This critical temperature also defines two distinct temperature ranges: the low-temperature (303–413 K) and the high-temperature (423–463 K) regimes, where the ionic transport mechanism switches from the normal ionic transport to a vacancy-mediated ionic transport mechanism. A substantially high activation energy $\sim 1.82\left(\pm 0.02\right)\mathrm{eV}$ is calculated from the Arrhenius plot of the ionic conductivity in the high-temperature region, while at the low-temperature region, the activation energy is found to be $\sim 0.48\left(\pm 0.02\right)\mathrm{eV}$. The abrupt jump in the ionic conductivity beyond the critical temperature is attributed to the onset of the anionic vacancy-mediated enhanced ionic conductivity. Polaronic models have been used to interpret the AC conductivity and its power-law exponent. The activation energy obtained from ionic conductivity measurements is consistent with those calculated from relaxation time using the HN and KWW models. The presence of two master curves in time-temperature superposition scaling of AC conductivity and modulus loss spectra specifies the validity of two different conduction mechanisms.

In the process of diminishing the safety concerns of sodium-ion batteries, the development of glass-based solid electrolyte materials has received adequate interest. Nevertheless, achieving a high ionic-conductivity at room temperature for glass materials remains a challenging task because of the poor correlation between the conductivity and the glass structure. Here, we attempt to understand the effective influence of NaCl on the structure and ionic-conductivity of the phosphate-based glass network. For this study, $x\mathrm{NaCl}\text{−}(100\text{−}x$) ($31.725{\mathrm{Na}}_2\mathrm{O}\text{−}12.69{\mathrm{Al}}_2{\mathrm{O}}_3\text{−}31.725{\mathrm{P}}_2{\mathrm{O}}_5\text{−}8.46\mathrm{NaF}\text{−}5.40{\mathrm{Na}}_2{\mathrm{SO}}_4\text{−}10{\mathrm{MoO}}_3$) glass systems (mol %) were selected, where $x=0$, 5, 10, 15, and 20 mol %. To investigate structural changes with the addition of different NaCl concentrations, ${}^{27}\mathrm{Al}, {}^{23}\mathrm{Na}, {}^{31}\mathrm{P}$ magic angle spinning nuclear magnetic resonance (MAS-NMR), ${}^{31}\mathrm{P}$ two-dimensional (2D) phase-adjusted spinning sideband (PASS), and ${}^{31}\mathrm{P}$ 2D J-resolved NMR techniques and Raman spectroscopic techniques were utilized. Impedance spectroscopy and ac conductivity spectra were used to assess ionic-conductivity and sodium-ion dynamics, respectively. Impedance spectral analysis reveals that the ionic-conductivity of the base glass is increased by 2.4 times (from 1.85 × ${10}^{-7}$ to 4.44 × ${10}^{-7}$ S/cm at 373 K) with the addition of 20 mol % of NaCl. Raman spectra confirm the presence of P−O−Mo and the absence of Mo−O−Mo bonds in these glass systems, and ${}^{31}\mathrm{P}$ 2D J-resolved spectra indicate the absence of P−O−P bonds. Upon increasing the NaCl concentration, significant changes in the shapes of ${}^{31}\mathrm{P}$ and ${}^{27}\mathrm{Al}$ MAS-NMR spectra were observed, indicating the effective influence of NaCl on the distribution of alumina and phosphorus structural units. Irrespective of the temperature, sodium-ion dynamic studies show that the mean-square displacement $\langle R^2\left(t_p\right)\rangle$ decreases with increasing NaCl concentration up to 10 mol % and then increases with a further increase in NaCl concentration. This investigation aids in understanding the sodium-ion dynamics and the structural information of a multicomponent glass system to enhance the room-temperature conductivity.

We present an experimental study of the collective dynamics of lithium-ammonia solutions in order to investigate the role played by the metallic character of the liquid on the atomic dynamics and the relevance of almost free ammonia. To understand the intrinsically complex dynamical behavior due to the presence of clusters composed of at least four ammonia molecules coordinated by a Li atom, we measured the neutron dynamic structure factor in an extended region of wave-vector transfer $Q$, i.e., from a value as low as $0.2{\AA }^{-1}$ up to $2.4{\AA }^{-1}$, going beyond the limit of twice the Fermi wave vector $2k_F\simeq 0.98{\AA }^{-1}$. This allowed us to probe the system with wavelengths between $\approx 3\AA$ (comparable with the ammonia size) and $\approx 30\AA$, a range ensuring a good sensitivity to the collective atomic motions, where the metallic character is known to play a major role. Three different Li concentrations (0.10, 0.17, and 0.20 molar fraction) have been analyzed at 220 K and, in the case of the intermediate concentration, the behavior at 155 K (still in the liquid phase) has also been explored. The effect of the metallic nature, dominated by the electron response when $Q<2k_F$, is confirmed down to 0.1 molar fraction but, thanks to the availability of better data and the synergy enabled by the simultaneous analysis of neutron and previous x-ray data, we were able to detect the presence of a second excitation affecting the global dynamics of the system. This second mode shows, with respect to the acoustic collective mode, an increasing energy-integrated intensity as $Q$ grows, i.e., in a range where the data obviously better reveal the local (short length scale) atomic behavior. Finally, by comparing the results of the mentioned analysis with those obtained recently by techniques specially focused on the intrinsic metallic properties, like photoemission spectroscopy, it has been possible to correlate the dynamics with the presence of metallic clusters, at almost constant electron density, embedded into free fluid ammonia. The present results also allow for a coherent interpretation of the elastic behavior of lithium ammonia solutions, as determined by ultrasound velocity data in a rather wide concentration range, and the identification of the different concentration regions where agreement with the interacting electron gas paramagnetic response and velocity of collective mode is obtained. Whether the dispersion curve anomaly at $\approx 2k_F$ (observed down to 0.1 molar fraction also for the second mode) is simply related to the dielectric response or some other mechanism may also contribute to this phenomenon, remains an open question.

Perovskites are promising materials candidates for optoelectronics, but their commercialization is hindered by toxicity and materials instability. While compositional engineering can mitigate these problems by tuning perovskite properties, the enormous complexity of the perovskite materials space aggravates the search for an optimal optoelectronic material. We conducted compositional space exploration through Monte Carlo (MC) convex hull sampling, which we made tractable with machine learning (ML). The ML model learns from density functional theory calculations of perovskite atomic structures, and can be used for quick predictions of energies, atomic forces, and stresses. We employed it in structural relaxations combined with MC sampling to gain access to low-energy structures and compute the convex hull for $\mathrm{CsPb}{\left({\mathrm{Br}}_{1-\mathrm{x}}{\mathrm{Cl}}_{\mathrm{x}}\right)}_3$. The trained ML model achieves an energy prediction accuracy of 0.1 meV per atom. The resulting convex hull exhibits two stable mixing concentrations at $1/6$ and $1/3$ Cl contents. Our data-driven approach offers a pathway towards studies of more complex perovskites and other alloy materials with quantum mechanical accuracy.

Anti-Ruddlesden-Popper (ARP) phase oxide perovskites ${\mathrm{Ca}}_4\mathrm{O}{A}_2$ $(A=\mathrm{P}, \mathrm{As}, \mathrm{Sb}, \mathrm{Bi})$ have recently attracted great interest in the field of ferroelectrics and thermoelectrics, whereas their optoelectronic application is limited by their indirect band gaps. In this work, we introduce $A$-site anion ordering in ${\mathrm{Ca}}_4\mathrm{O}{A}_2$ $(A=\mathrm{P}, \mathrm{As}, \mathrm{Sb}, \mathrm{Bi})$, and find that it induces an indirect-to-direct band gap transition. Using first-principles calculations, we study the ground-state structures, electronic structure, transport properties and optical properties of anion-ordered ARP phase oxide perovskites ${\mathrm{Ca}}_4\mathrm{O}A{A}^{\prime }$. Based on analyses of the lattice dynamics, the ground-state structures of ${\mathrm{Ca}}_4\mathrm{OAsSb}$ and ${\mathrm{Ca}}_4\mathrm{OAsBi}$ are identified in $P4/nmm$ symmetry and those of ${\mathrm{Ca}}_4\mathrm{OPSb}$ and ${\mathrm{Ca}}_4\mathrm{OPBi}$ are in the $I222$ symmetry. In contrast to the Ruddlesden-Popper (RP) phase oxide and halide counterparts, ${\mathrm{Ca}}_4\mathrm{O}A{A}^{\prime }$ $(A{A}^{\prime }=\mathrm{PSb}, \mathrm{PBi}, \mathrm{AsSb}, \mathrm{AsBi})$ show larger band dispersion along the out-of-plane direction, smaller band gaps and highly enhanced out-of-plane mobilities, which results from the short interlayer distances and the enhanced covalency of the pnictides. Although the out-of-plane mobilities of these $n=1$ ARP phase perovskites highly increase, the comparatively strong polar optical phonon scattering limits the further enhancement of their mobilities. Furthermore, compared to RP phase halide ${\mathrm{Cs}}_2{\mathrm{PbI}}_2{\mathrm{Cl}}_2$, ${\mathrm{Ca}}_4\mathrm{O}A{A}^{\prime }$ show strong optical absorption around the band edges, and their optical absorption coefficients can reach ${10}^5\mathrm{c}{\mathrm{m}}^{-1}$ within the visible light region due to small band gaps. This study reveals that these ARP phase oxide perovskites exhibit the potential for optoelectronic applications.

Uranium ditelluride $\left({\mathrm{UTe}}_2\right)$ has attracted recent interest due to its unique superconducting properties, which include the potential for a topological odd-parity superconducting state. Recently, ac-calorimetry measurements under pressure indicate a change in the ground state of ${\mathrm{UTe}}_2$ from superconducting to antiferromagnetic at 1.4 GPa. Here, we investigate the effect of pressure on the crystal structure of ${\mathrm{UTe}}_2$ up to 25 GPa at room temperature using x-ray diffraction. We find that ${\mathrm{UTe}}_2$, which at ambient conditions has an orthorhombic (Immm) structure, transforms to a body-centered tetragonal $(I4/mmm)$ structure at 5 GPa in a quasihydrostatic neon (Ne) pressure-transmitting medium. In the absence of a pressure-transmitting medium, this transformation occurs between 5 and 8 GPa. The data were fit with a third-order Birch-Murnaghan equation of state resulting in values of $B_0=46.0\pm 0.6\mathrm{GPa}$, $B^{\prime }=9.3\pm 0.5$ (no pressure medium), and $B_0=42.5\pm 2.0\mathrm{GPa}$, $B^{\prime }=9.3$ (fixed) (neon pressure medium) for the Immm phase. For the $I4/mmm$ phase, $B_0=78.9\pm 0.5\mathrm{GPa}$ GPa and $B^{\prime }=4.2\pm 0.1$ (no pressure-transmitting medium), and $B_0=70.0\pm 1.1\mathrm{GPa}$ and $B^{\prime }=4.1\pm 0.2$ (neon pressure medium). The high-pressure tetragonal phase is retained after decompression to ambient pressure, with approximately $30\%$ remaining after 2 days. We argue that the observed phase transition into a higher-symmetry structure at $P\sim 5\mathrm{GPa}$ (orthorhombic to tetragonal) is accompanied by an increase in the shortest distance between uranium atoms from 3.6 Å (orthorhombic) to 3.9 Å (tetragonal), which suggests localization of the $5f$ electrons, albeit with a 10.7% decrease in volume.

We exhaustively search quaternary metal hydrides based on the (13-2-1) and (13-3-1) structures that are two of the putative densest ternary sphere packings in cubic systems [R. Koshoji et al., Phys. Rev. E 104, 024101 (2021)]. The 73 304 candidate hydrides are generated by substituting the small spheres with hydrogen atoms, and the medium, large, and fourth spheres with metallic atoms. Specifically, the substitution of the small spheres with hydrogen atoms gives the unconventional hydrogen sublattices. We screen unstable hydrides in the candidates through geometrical optimizations, constant pressure molecular dynamics simulations, and phonon calculations under hydrostatic pressure of 10 GPa, and identify 23 hydrides with static and dynamic stability, including ${\mathrm{H}}_{12}{\mathrm{ScY}}_2\mathrm{La}$ and ${\mathrm{H}}_{12}\mathrm{Ti}{\mathrm{Ni}}_3\mathrm{Ba}$. The superconducting transition temperatures $T_c$, calculated by density functional theory for superconductors, are found to be 5.7 and 6.7 K for the selected two hydrides ${\mathrm{H}}_{12}{\mathrm{ScY}}_2\mathrm{Ca}$ and ${\mathrm{H}}_{12}{\mathrm{ScY}}_2\mathrm{Sr}$, respectively. We expect that the 23 candidates of hydrides screened by the exhaustive search for 73 304 hydrides provide a guideline to narrow down the search space for trials in the experimental synthesis of quaternary metal hydrides.

We present a detailed study of the electronic properties and lattice dynamics of bulk and mono-, bi- and tri-tetralayer β-InSe by means of density functional and density functional perturbation theory. We show that the few-layers systems are semiconductors with an indirect nature of the fundamental band gap and a Mexican-hat-shape of the top valence band. The phonon branches analysis reveals the dynamical stability of a mono- and bi-tetralayer systems considered together with the longitudinal-optical–transverse-optical splitting breakdown toward one tetralayer. In-plane and out-of-plane zone-center lattice vibrations dominate the Raman and IR spectra. Small shifts of the peak positions but stronger variations of the peak intensities are observed as signatures of the number of layers.