Ground-state Structure Research Articles

Directed Electrostatics Strategy Integrated as a Graph Neural Network Approach for Accelerated Cluster Structure Prediction.

We present a directed electrostatics strategy integrated as a graph neural network (DESIGNN) approach for predicting stable nanocluster structures on their potential energy surfaces (PESs). The DESIGNN approach is a graph neural network (GNN)-based model for building structures of large atomic clusters with specific sizes and point-group symmetry. This model assists in the structure building of atomic metal clusters by predicting molecular electrostatic potential (MESP) topography minima on their structural evolution paths. The DESIGNN approach is benchmarked on the prototype Mgn clusters with n < 150. The predicted MESP topography minima of Mgn clusters, n < 70, fairly agrees with the whole-molecule MESP topography calculations. Moreover, the ground-state structures of Mgn (n = 4-32) clusters generated through the DESIGNN approach corroborate well with the global minimum structures reported in the literature. Furthermore, this approach could generate novel symmetric isomers of medium to large Mgn clusters in the size regime, n < 150, by constraining the point-group symmetry of the parent clusters. The parent growth potential (GP) of a cluster gives a measure of its parent cluster to accommodate more atoms and characterize the structures on the DESIGNN-guided path. The GP of a cluster can also be interpreted as a measure of the cooperative interaction relative to its parent cluster. Along the highest GP paths, the DESIGNN approach is further employed to generate stable Mgn nanoclusters with n = 228, 236, 257, 260. Therefore, the DESIGNN approach holds great promise in accelerating the structure search and prediction of large metal clusters guided through MESP topography.

Theoretical exploration of structural, electronic, elastic, mechanical, and thermodynamic properties of MgCu4Sn intermetallic compound for engineering applications: first-principle calculations

The structural, electronic, elastic, mechanical, and thermodynamic properties of the ternary MgCu4Sn intermetallic compound are investigated by means of first-principle calculations within density functional theory (DFT), in combination with the quasi-harmonic Debye model. Local density approximation (LDA) and generalized gradient approximation (GGA) are made for electronic exchange–correlation potential energy. The lattice constant is in good agreement with experimental data. We determine the elastic constant tensor of the compound from the calculated stress–strain relation in both approximations. Once the elastic constants are obtained, the bulk modulus B, shear modulus G, Young’s modulus E, Poisson’s ratio ν, anisotropy factor A, and the ratio B/G for MgCu4Sn compound were deduced using Voigt-Reuss-Hill (VRH) approximation. The ground-state structure of MgCu4Sn is predicted to be thermodynamically and mechanically stable. The obtained band structure and density of states reveal metallic character of MgCu4Sn. The calculation results show also that this intermetallic crystal is a stiff, elastically anisotropic and ductile material. The Debye temperature is also determined from elastic constants. The temperature dependence of the constant volume heat capacity Cv, the entropy S, and the volumetric thermal expansion coefficient α in a quasi-harmonic approximation have been obtained from calculated energy E as a function of the volume V of a MgCu4Sn crystal and discussed for the first report.

Charge-transfer complexation of coordination cages for enhanced photochromism and photocatalysis

Intensified host-guest electronic interplay within stable metal-organic cages (MOCs) presents great opportunities for applications in stimuli response and photocatalysis. Zr-MOCs represent a type of robust discrete hosts for such a design, but their host-guest chemistry in solution is hampered by the limited solubility. Here, by using pyridinium-derived cationic ligands with tetrakis(3,5-bis(trifluoromethyl)phenyl)borate (BArF−) as solubilizing counteranions, we report the preparation of soluble Zr-MOCs of different shapes (1-4) that are otherwise inaccessible through a conventional method. Enforced arrangement of the multiple electron-deficient pyridinium groups into one cage (1) leads to magnified positive electrostatic field and electron-accepting strength in favor of hosting electron-donating anions, including halides and tetraarylborates. The strong charge-transfer (CT) interactions activate guest-to-host photoinduced electron transfer (PET), leading to pronounced and regulable photochromisms. Both ground-state and radical structures of host and host-guest complexes have been unambiguously characterized by X-ray crystallography. The CT-enhanced PET also enables the use of 1 as an efficient photocatalyst for aerobic oxidation of tetraarylborates into biaryls and phenols. This work presents the solution assembly of soluble Zr-MOCs from cationic ligands with the assistance of solubilizing anions and highlights the great potential of harnessing host-guest CT for boosting PET-based functions and applications.

Structural evolution and electronic properties of neutral boron-doped nitrogen clusters

Clusters represent intermediate states between isolated atoms and bulk solids. They serve as model systems to elucidate the physical properties of compounds from the atomic or molecular scale to the macroscopic bulk phase. Here, we perform thorough structure searches of neutral boron doped nitrogen clusters by crystal structural analysis by particle swarm optimization cluster structural prediction and density functional theory calculations. The calculated results indicate that the ground state structures of BNn(n= 4-16) clusters are evolutional from one-dimensional chains to two dimensional rings, and finally to three-dimensional (3D) geometries. Interestingly, the intriguing BN12cluster, characterized by a 3D configuration with a central boron atom connecting four N3chains in distinct directions, exhibits exceptional stability. The chemical bonding analysis reveals that the outstanding stability of BN12cluster is attributed to the strongσandπinteractions between the 2porbitals of the boron atom and the surrounding nitrogen atoms, as well as the robustσbonds along the four nitrogen chains. The present findings offer important insights for understanding the geometries and electronic properties of neutral boron doped nitrogen clusters and provide an avenue for the design and synthesis of nitrogen-rich compounds.

Intrinsic Coexistence of Miscibility and Segregation in Gold-Silver Nanoalloys.

Bimetallic nanoparticles are used in numerous applications in catalysis, plasmonics or fuel cell technology. The addition of the second metal to the nanoparticles allows enhancing and fine-tuning their properties by choosing their composition, size, shape and environment. However, the crucial additional parameter of chemical structure within the particle is difficult to predict and access experimentally, even though segregated core-shell structures and random alloys can have drastically different physicochemical properties. This is highlighted by the vast literature on the most studied bimetallic system, gold-silver, for which the controversy on whether gold and silver are miscible on the nanoscale or segregate persists. Here, these contradictions are solved by determining quantitatively the coexistence of an alloyed core and a 1-2nm thick shell with gradual silver enrichment as the chemical ground state structure. Chemical reactions with the environment and meta-stable structures are furthermore identified as responsible for the contradictions in the literature. This method is applicable to other multi-metallic systems, provides benchmark input for theoretical models, and forms the basis for studying chemical rearrangements under reactive conditions in catalysis.

Reconstructing real-space geometries of polyatomic molecules undergoing strong field laser-induced Coulomb explosion

Coulomb explosion is an established momentum imaging technique, where the molecules are ionized multiple times on a femtosecond time scale before breaking up into ionized fragments. By measuring the momentum of all the ions, information about the initial molecular structure is theoretically available. However, significant geometric changes due to multiple ionizations occur before the explosion, posing a challenge in retrieving the ground-state structure of molecules from the measured momentum values of the fragments. In this work, we investigate theoretically and experimentally such a connection between the ground-state geometry of a polyatomic molecule (OCS) and the detected momenta of ionic fragments from the Coulomb explosion. By relying on time-dependent density functional theory (TDDFT), we can rigorously model the ionization dynamics of the molecule in the tunneling regime. We reproduce the energy release and the Newton plot momentum patterns of an experiment in which OCS is ionized to the 6+ charge state. Our results provide insight into the behavior of molecules during strong field multiple ionization, opening a way toward precision imaging of real-space molecular geometries using tabletop lasers.

Single-Molecule Magnet Behavior and Spin Structure of an FeIII7 Cartwheel Cluster Revealed by Sub-Kelvin Magnetometry and Mössbauer Spectroscopy: The Final Pieces of the Puzzle.

The spin frustration and other magnetic properties of the "cartwheel" heptanuclear cluster [FeIII7O3(O2CtBu)9(Me-dea)3(H2O)3] (Me-deaH2 = N-methyldiethanolamine) have been previously investigated; we present here a Mössbauer spectroscopic study and sub-Kelvin magnetization and ac susceptibility measurements which enable a complete magnetic picture of this frustrated cluster. 57Fe Mössbauer spectra above 150 K showed three doublets in a 1:3:3 ratio, which could be assigned by their respective quadrupole splittings to the central Fe(1) and the peripheral Fe(2) and Fe(3). The field dependence of the corresponding magnetic sextets at 3 K showed that the spins on the central Fe(1) and the three peripheral Fe(2) sites with O5N coordination are oriented mutually coparallel, while these are antiparallel to the spins on the peripheral Fe(3) sites with O6 coordination, resulting in an overall S = 5/2 ground state. This provides experimental confirmation of the previously proposed spin ground state structure. Upon cooling to sub-Kelvin temperatures, a crossover to spin blocking with TB ≈ 0.21 K could be observed. This single-molecule magnet behavior had been expected but had not been observable with a conventional SQUID. The anisotropy barrier, of 3-fold symmetry, can be described in terms of the parameter D/kB = -0.47 K and a fourth-order perturbation; the latter enables thermally activated quantum tunneling through the excited sublevel mz = ± 3/2, with an activation barrier of U/kB = 1.9 K.

Symmetry Breaking of Electronic Structure upon the π→π* Excitation in Anthranilic Acid Homodimer.

The main purpose of this study is to characterize the nature of the low-energy singlet excited states of the anthranilic acid homodimer (AA2) and their changes (symmetry breaking) caused by deformation of the centrosymmetric, ground state structure of AA2 towards the geometry of the S1 state. We employ both the correlated ab initio methods (approximate Coupled Clusters Singles and Doubles-CC2 and CASSCF/NEVPT2) as well as the DFT/TDDFT calculations with two exchange-correlation functionals, i.e., B3LYP and CAM-B3LYP. The composition of the wavefunctions is investigated using the one-electron transition density matrix and difference density maps. We demonstrate that in the case of AA2, small asymmetric distortions of geometry bring about unproportionally large changes in the excited state wavefunctions. We further provide comprehensive characterization of the AA2 electronic structure, showing that the excitation is nearly completely localized on one of the monomers, which stands in agreement with the experimental evidence. The excitation increases the π-electronic coupling of the substituents and the aromatic ring, but only in the excited monomer, while the changes in the electronic structure of the unexcited monomer are negligible (after geometry relaxation). The increased electronic density strengthens both intra- and intermolecular hydrogen bonds formed by the carbonyl oxygen atom of the excited monomer, making them significantly stronger than in the ground state. Although the overall pattern of changes remains qualitatively consistent across all methods employed, CC2 predicts more pronounced excitation-induced modifications of the electronic structure compared to the more routinely used TDDFT approach. The most important deficiency of the B3LYP functional in the present context is locating two charge-transfer states at erroneously low energies, in close proximity of the S1 and S2 states. The range-corrected CAM-B3LYP exchange-correlation functional gives a considerably improved description of the CT states at the price of overshot excitation energies.

Investigation of the Structural, Vibrational, Electronic, and optical properties of energetic Nitrogen-Rich azidotetrazolates XCN7 (X = N2H5, NH4, K, Cs)

In this work, we present a detailed and comparative study of four salts of 5-azido-1H-tetrazole using Density Functional Theory (DFT) based computational methods. The salts, containing the CN7- anion, include hydrazinium azidotetrazolate (N2H5CN7), ammonium azidotetrazolate (NH4CN7), potassium azidotetrazolate (KCN7), and cesium azidotetrazolate (CsCN7). These compounds are collectively represented as XCN7, where X = N2H5, NH4, K, and Cs. We found that the incorporation of van der Waals interactions was crucial in aligning the theoretical ground state structures with experimental data. Mechanical stability of all the compounds within their respective space groups was verified by calculating the elastic constants and bulk modulus. Vibrational frequency analysis revealed that N2H5CN7 and NH4CN7, containing NH bonds, exhibited frequencies around 3300 cm−1, while the metal salts KCN7 and CsCN7, lacking NH bonds, showed frequencies below 2000 cm−1. Born effective charge calculations indicated strong covalency within the tetrazole ring and between C, N, and H atoms, contrasted by the ionic nature of the metal atoms. Using the TB-mBJ potential, we accurately computed the electronic structure and optical properties, predicting bandgaps and absorption edges for these XCN7 compounds. The partial density of states analysis highlighted the significant role of C and N p states in the sensitivity of these compounds. Optical property evaluations confirmed that these compounds are optically anisotropic, exhibiting low sensitivity in the visible region but high sensitivity in the UV and far UV regions. These insights are crucial for predicting and controlling their reactivity, stability, and performance in various applications, particularly in the field of energetic materials.

First Principles Calculation of Sodium Intercalation in Transition-Metal Dichalcogenides

Sodium ion batteries (SIBs) are an attractive substitute to lithium ion batteries, particularly for grid-scale energy storage, due to low cost and abundance of sodium [1]. Two-dimensional (2D) transition-metal dichalcogenides (TMDs) have evoked widespread attention as promising electrode materials [2], particularly as potential anode materials. Based on a database of 2D-TMDs, there is a need to determine the stability of 3D-TMDs before/after sodiation to optimise SIB anode materials.In this work, using density functional theory (DFT) calculations, we conduct a systematic study of the series of TMDs for their electrochemical performance and structural properties based on 2D ground state structure of TMDs [3,4]. A voltage map is presented where the sodiated voltage of 3D-TMDs can be consulted, including p-MoS2, p-CdI2, p-NbTe2, p-WTe2, p-PdS2 and p-PdCl2 prototypes. With this voltage map, we can explore which TMDs can be as a suitable electrode materials for SIBs. Group VI elements (Mo, W) emerge as promising candidate from the voltage map. Further exploration of these candidates reveals that a prismatic → octahedral phase transition occurred during sodiation for CrS2, MoS2, CrSe2 and WS2, while MoSe2 and WSe2 show low voltage in prismatic coordination without phase transition. Some of Mo and W systems appearing to be promising anode materials because of relatively low voltage. However, phase transition during sodiation of CrS2, MoS2, CrSe2 and WS2 leads to an increase in voltage, making these less effective as anode materials.Additionally, the phase changes could be associated with other detrimental volume changes, hysteresis and possible degradation issues. Keywords: transition-metal dichalcogenides, sodium-ion batteries, phase transition during sodiation, first principles calculation. Reference [1] Kundu, D., Talaie, E., Duffort, V. & Nazar, L. F. The emerging chemistry of sodium ion batteries for electrochemical energy storage. Angewandte Chemie - International Edition 54, 3432–3448 (2015).[2] J Morales, J Santos, and J L Tirado. Electrochemical studies of lithium and sodium intercalation in MoSe2. Solid State Ionics, 83:57–64, 1996.[3] Andrea Silva, Jiangming Cao, Tomas Polcar, and Denis Kramer. Design guidelines for two-dimensional transition metal dichalcogenide alloys. Chemistry of Materials, 34:10279–10290, 2022.[4] Andrea Silva, Jiangming Cao, Tomas Polcar, and Denis Kramer. Pettifor maps of complex ternary two-dimensional transition metal sulfides. npj Computational Materials, 8(1):178, 2022.

Heterojunction Organic Solar Cells with Efficient Charge Mobility and Separation Capabilities Studied by DFT.

The properties of the active layer materials play a decisive role in determining the power conversion efficiency of organic solar cells (OSCs). Chlorophyll and its derivatives are abundant and environmentally friendly functional organic molecular materials. Using density functional theory (DFT) and time-dependent density functional theory (TD-DFT), we have calculated the absorption spectra and their excited state properties based on optimized ground state structures. It was found that bacteriochlorin exhibits superior structural properties, a smaller energy gap and hole reorganization energy, redshifted absorption spectra, and higher hole mobility compared to the donor D18. This suggests that bacteriochlorin exhibits superior donor properties. Comparative studies between o-AT-2Cl and m-AT-2Cl showed that o-AT-2Cl had superior acceptor properties, implying that differences in substitution positions can influence the physicochemical properties of non-fullerene acceptors (NFAs). Subsequently, six bulk heterojunctions (BHJs) were constructed by combining three donors with nonfused ring electron acceptors, o-AT-2Cl and m-AT-2Cl. The bacteriochlorin-based BHJs performed well among them, with BChl3/o-AT-2Cl and BChl4/o-AT-2Cl having the largest interfacial charge separation rate. The results suggested that BHJs composed of bacteriochlorin and NFAs can improve OSCs' photovoltaic performance, providing a feasible scheme for designing efficient OSCs.

Superconductivity and strain-enhanced phase stability of Janus tungsten chalcogenide hydride monolayers

Janus transition metal-dichalcogenide materials have attracted a great deal of attention due to their remarkable physical properties arising from the two-dimensional geometry and the breakdown of the out-of-plane symmetry. Using first-principles density functional theory, we investigated the phase stability, strain-enhanced phase stability, and superconductivity of Janus WSeH and WSH. In addition, we investigated the contribution of the phonon linewidths from the phonon energy spectrum responsible for the superconductivity and the electron-phonon coupling as a function of phonon wave vectors and modes. Previous work has examined hexagonal 2H and tetragonal 1T structures, but we found that neither is a ground-state structure. The metastable 2H phase of WSeH is dynamically stable with Tc≈11.60K, similar to WSH. Compressive biaxial strain—the two-dimensional equivalent of pressure—can stabilize the 1T structures of WSeH and WSH with Tc≈9.23K and 10.52 K, respectively. Published by the American Physical Society 2024

Atomic-scale investigation on the structures and mechanical properties of metastable grain boundaries in aluminum

Grain boundary (GB) structural transition in pure metals open up new possibilities for material microstructure design. By managing the distribution of ground-state and metastable GB structures, the beneficial effects of GBs on materials can be maximised. However, the application of GB transitions to develop high-performance aluminum is limited by the inadequate understanding of the metastable GB structure in aluminium and its associated plastic deformation mechanisms. In this work, we firstly used a high-throughput GB generation method to construct multiple GB structure for a given misorientation angle, and screen out the ground-state and metastable GB structures according to the energy principle. Six typical symmetrically tilted GBs were investigated, including Σ5(210), Σ17(410) and Σ17(530) GBs around <001> tilt axis, and Σ9(221), Σ11(332), Σ17(223) GBs around <110> axis. Then, molecular dynamics simulations were carried out to perform uniaxial tensile tests on the six GBs and their corresponding metastable GBs at different temperatures. The results show that the tensile strength of <001> metastable GBs differs slightly from the ground-state GB at various temperatures, but for <110> GBs, the strength of most metastable GBs is significantly stronger or weaker compared to that of ground-state GB at 10 K. An increase in temperature reduced this difference in tensile strength of <110> GBs. According to atomic analysis of the GB structural characteristics, it was found that stress and temperature-induced GB structural transition, GB strain localization, and the prevention of dislocation nucleation or propagation from the dissociated structure are the main causes of the differences in tensile responses between the ground-state and metastable GBs.

Excited-State Decay and Photolysis of O-Nitrophenol before Proton Transfer. I: A Theoretical Investigation in the Microsolvated Atmospheric Environment.

As a potential source of the hydroxyl (OH) radical and nitrous acid (HONO), photolysis of o-nitrophenol (ONP) is of significant interest in both experimental and theoretical studies. In the atmospheric environment, the number of water molecules surrounding ONP changes with the humidity of the air, leading to an anisotropic chemical environment. This may have an impact on the photodynamics of ONP and provide a mechanism that differs from previously reported ones in the gas phase or in solution. Herein, the high-level MS-CASPT2//CASSCF method was performed to elucidate the excited-state decay and the generation of the OH radical for ONP before proton transfer in the microsolvated surrounding. We found that the varying number of water molecules affects the ground-state structures and alters the energy levels of nπ* and ππ* at the Franck-Condon (FC) region. Nevertheless, this is not the case for the excited-state minima, which exhibit very similar adiabatic excitation properties. In addition, the presence of water molecules also significantly influences the intersection structures since hydrogen bonds will hinder or alleviate the rotation or pyramidalization of the nitro (NO2) group. This will, in turn, change the excited-state relaxation mechanism of ONP. Finally, we speculated that the OH radical might be formed in the hot ground state of ONP in the microsolvated surrounding after exploring all possible electronic states.

Decoding the structural and electronic variations in M2Bn- (M = Sc, Y, La; n = 6–9) clusters: Insights for nanomaterial design

A series of low-lying energy isomers of M2Bn- (M = Sc, Y, La; n = 6–9) clusters were investigated using density functional theory. By conducting functional tests and comparing with reported experimental photoelectron spectra, we confirmed that when n = 6 − 8, their ground-state structures are nearly identical, differing only in the distance between the M atom and the boron skeleton. Moreover, for n = 7–8, all ground states exhibit consistent inverse-sandwich structures. However, for n = 9, three systems exhibit different types of ground-state structures: The Sc-doped system has a quasi-inverse-sandwich structure, the Y-doped system has two possible coexisting structures, and the La-doped system has an inverse-sandwich structure. Subsequent average binding energy analyses, chemical bonding analyses and stability analyses further elucidated the reasons. Our research provides theoretical insights for a deeper understanding of the various properties of clusters doped with different elements and for exploring potential building blocks for nanomaterials.

Quantitatively Deciphering the Local Structure and Luminescence Spectroscopy of Pr3+-Doped Yttrium Lithium Fluoride.

Praseodymium (Pr3+)-doped LiYF4 nanophosphors have garnered significant interest for their potential applications in lasers, phosphors, and quantum memories. However, there remains a lack of comprehensive research on the local coordination environment and luminescence spectroscopy of Pr3+:LiYF4 nanocrystals. This study presents the first investigation of the ground-state structure of Pr3+:LiYF4 crystals by employing the crystal structure prediction method, and a [PrF8]5- ligand complex with S4 local symmetry is determined. The complete energy levels of the Pr3+ ions in LiYF4 nanocrystals are unveiled by using our newly developed well-established parametrization matrix diagonalization method. A novel set of free-ion and crystal-field parameters is derived through a good simulation with 45 experimental energy levels. Many of the emissions of Pr3+-doped LiYF4 are successfully reproduced based on Judd-Ofelt theory, and these transitions are comparable to the experimental ones. Moreover, two new prominent emission bands with their peaks at 675 and 849 nm originating from 1I6 → 3F4 and 1I6 → 1G4 transitions, respectively, are predicted by us for the first time. This study could provide a feasible method to search for practical laser transition channels of solid-state lasers based on Pr3+: LiYF4 nanophosphors.

Novel Dissymmetric Formal Quinoidal Molecules End-Capped by Dicyanomethylene and Triphenylphosphonium.

A number of quinoidal molecules with symmetric end-capping groups, particularly dicyanomethylene units, have been synthesized for organic optoelectronic materials. In comparison, dissymmetric quinoidal molecules, characterized by end-capping with different groups, are less explored. In this paper, we present the unexpected formation of new formal quinoidal molecules, which are end-capped with both dicyanomethylene and triphenylphosphonium moieties. The structures of these dissymmetric quinoidal molecules were firmly verified by single crystal structural analyses. On the basis of the control experiments and DFT calculations, we proposed the reaction mechanism for the formation of these dissymmetric quinoidal molecules. The respective zwitterionic forms should make contributions to the ground state structures of these quinoidal molecules based on the analysis of their bond lengths and aromaticity and Mayer Bond Orbital (MBO) calculation. This agrees well with the fact that negative solvatochromism was observed for these quinoidal molecules. Although these new quinoidal molecules are non-emissive both in solutions and crystalline states, they become emissive with quantum yields up to 51.4 % after elevating the solvent viscosity or dispersing them in a PMMA matrix. Interestingly, their emissions can also be switched on upon binding with certain proteins, in particular with human serum albumin.

Novel Dissymmetric Formal Quinoidal Molecules End‐Capped by Dicyanomethylene and Triphenylphosphonium

AbstractA number of quinoidal molecules with symmetric end‐capping groups, particularly dicyanomethylene units, have been synthesized for organic optoelectronic materials. In comparison, dissymmetric quinoidal molecules, characterized by end‐capping with different groups, are less explored. In this paper, we present the unexpected formation of new formal quinoidal molecules, which are end‐capped with both dicyanomethylene and triphenylphosphonium moieties. The structures of these dissymmetric quinoidal molecules were firmly verified by single crystal structural analyses. On the basis of the control experiments and DFT calculations, we proposed the reaction mechanism for the formation of these dissymmetric quinoidal molecules. The respective zwitterionic forms should make contributions to the ground state structures of these quinoidal molecules based on the analysis of their bond lengths and aromaticity and Mayer Bond Orbital (MBO) calculation. This agrees well with the fact that negative solvatochromism was observed for these quinoidal molecules. Although these new quinoidal molecules are non‐emissive both in solutions and crystalline states, they become emissive with quantum yields up to 51.4 % after elevating the solvent viscosity or dispersing them in a PMMA matrix. Interestingly, their emissions can also be switched on upon binding with certain proteins, in particular with human serum albumin.

What is the true ground state of intermetallic compound Fe3Al?

We discuss recent doubts about the true ground-state (GS) structure of the intermetallic compound Fe3Al. It seems that it should be the D03 structure (observed experimentally), but there are some considerations that, perhaps, D03 might be a high-temperature (>400 K) structure and the GS at 0 K might be the L12 structure because there might be a high energy barrier between both structures and, when the temperature is lowered, the system is not able to transform into the (perhaps) lower-energy L12 structure. To elucidate this problem, we re-interpret our recent extended ab initio electronic structure calculations for Fe3Al performed with the help of the VASP code and using various exchange-correlation energies within the generalized gradient approximation (GGA). Regrettably, some calculations provide the L12 and some of them D03 as the GS structure.To resolve this question, we performed further calculations testing 9 frequently applied metaGGAs, such as TPSS, revTPSS, M06-L, SCAN(-L), rSCAN(-L) and r2SCAN(-L) representing a higher rung of the Jacob's ladder. It turns out that also here some meta-GGAs lead to L12 and some others to D03 GS structure and, again, we cannot decide.In this way, the present results represent the very first step on the way to understand the energetics of the Fe3Al compound and its ground state. We hope they may motivate future theoretical and experimental work in this direction.

GdWN3 is a nitride perovskite

Nitride perovskites ABN3 are an emerging and highly underexplored class of materials that are of interest due to their intriguing calculated ferroelectric, optoelectronic, and other functional properties. Incorporating novel A-site cations is one strategy to tune and expand such properties; for example, Gd3+ is compelling due to its large magnetic moment, potentially leading to multiferroic behavior. However, the theoretically predicted ground state of GdWN3 was a non-perovskite monoclinic structure. Here, we experimentally show that GdWN3−y crystallizes in a perovskite structure. High-throughput combinatorial sputtering with activated nitrogen is employed to synthesize thin films of Gd2−xWxN3−yOy with oxygen content y &amp;lt; 0.05. Ex situ annealing crystallizes a polycrystalline perovskite phase in a narrow composition window near x = 1. LeBail fits of synchrotron grazing incidence wide angle x-ray scattering data are consistent with a perovskite ground-state structure. Refined density functional theory calculations that included antiferromagnetic configurations confirm that the ground-state structure of GdWN3 is a distorted Pnma perovskite with antiferromagnetic ordering, in contrast to prior predictions. Initial property measurements find that GdWN3−y is paramagnetic down to T = 2 K with antiferromagnetic correlations and that the absorption onset depends on cation stoichiometry. This work provides an important path toward both the rapid expansion of the emerging family of nitride perovskites and understanding their potential multiferroic properties.