Nitrogen-doped graphene single-atom catalysts (SACs) have shown remarkable promise in selective hydrogenation and hydrogen storage. However, the rationalization of hydrogen evolution in these systems is still challenging. In this paper, by systematically calculating hydrogen adsorption and dissociation energies on active 3-fold sites M-C3-xNx, with x ranging from 0 to 3 and with M = Co, Ni, Pd, we show that hydrogen dissociation is endothermic─except for Pd-N3 and Pd-CN2─and proceeds via two distinct mechanisms, depending on the nitrogen content of the site. For nitrogen-poor sites, dissociation follows a heterolytic pathway with a relatively high activation energy (0.6-1.1 eV), with a notable exception being the Pd-C2N site with a low barrier (0.37 eV). In contrast, nitrogen-rich sites favor homolytic dissociation, with a significantly lower activation barrier (below 0.4 eV). However, for Ni-N3, the electronic confinement of hydrogen imposed by nitrogen neighbors prevents true homolytic dissociation, with the two dissociated H atoms on the metal spontaneously recombining. Across all N-doped graphene SAC models considered, the calculated activation barriers exhibit a Brønsted-Evans-Polanyi scaling. This study provides a detailed understanding of hydrogen dissociation on graphene SACs, paving the way for the design of catalysts tailored to specific applications.

This study identifies two new cubic γ-brass-type phases in the Ni-Zn-Ga system: (a) Ni2Zn11-xGax (0 < x ≤ 0.3) exist in a narrow homogeneity range, and the compounds crystallize in a cubic crystal system with space group of I4̅3m (a ≈ 9 Å), (b) Ni2Zn11-xGax (0.4 ≤ x ≤ 1.25) has a broader homogeneity range and the compounds in this region adopt the primitive cubic lattice with the space group P4̅3m (a ≈ 9 Å). The Ga insertion into Ni2Zn11 is site specific, and at the limiting composition, Ni2Zn9Ga1.25, the structure is completely ordered and comprises the two distinct clusters─a 26-atom γ-brass-type cluster (Ni4Zn18Ga4) and a 23-atom defect body-centered cubic (bcc)-type cluster (Ni4Zn18Ga1). The stability of these compounds can be rationalized by favorable enthalpies of formation obtained from the theoretical calculations, which correlate strongly with the coexistence of specific clusters within the primitive cubic unit cell. Electronic structure calculations indicate that these phases are stabilized by the Hume-Rothery mechanism, characterized by the presence of a pseudogap at the Fermi level. The chemical bonding analysis demonstrates that the interactions between Ni-Zn and Ni-Ga are crucial to the structural stability.

Despite significant research, the surface properties of quasicrystals and their approximants are not yet fully understood. In this paper, buckminsterfullerene (C60 fullerene) is used as a probe to test the adsorption properties of the (010) surface of the quasicrystalline approximant Al13Fe4. Using first-principles calculations, we systematically explore 17 distinct adsorption sites and identify several energetically favorable configurations. Our analysis reveals that the symmetry matching between the C60 molecule and the surface is a key parameter governing the interaction strength. Furthermore, surface aluminium atoms are shown to play a crucial role in stabilizing the adsorption. A comparative study with the Al13Co4(100) surface highlights similarities in the overall interaction trends, yet distinct differences arise due to variations in surface substructure. These findings underline the importance of both atomic composition and local geometric symmetry in molecule-intermetallic surface interactions.

Despite significant research, the surface properties of quasicrystals and their approximants are not yet fully understood. In this paper, buckminsterfullerene (C 60 fullerene) is used as a probe to test the adsorption properties of the (010) surface of the quasicrystalline approximant Al 13 Fe 4 . Using first-principles calculations, we systematically explore 17 distinct adsorption sites and identify several energetically favorable configurations. Our analysis reveals that the symmetry matching between the C 60 molecule and the surface is a key parameter governing the interaction strength. Furthermore, surface aluminium atoms are shown to play a crucial role in stabilizing the adsorption. A comparative study with the Al 13 Co 4 (100) surface highlights similarities in the overall interaction trends, yet distinct differences arise due to variations in surface substructure. These findings underline the importance of both atomic composition and local geometric symmetry in molecule–intermetallic surface interactions.

Intermetallic compounds have shown promising catalytic properties, exhibiting better selectivity and thermal stability than their metallic counterparts. Understanding their surface properties is crucial for optimizing catalytic performance. Here, we present an investigation of the atomic structure, chemical composition, and oxidation behavior of the previously unexplored binary intermetallic catalyst, Ni2In3, using various complementary techniques, including low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), x-ray photoelectron spectroscopy (XPS), and low-energy ion scattering (LEIS), which provides elemental information from the topmost surface layer. We also calculated the surface energy of several possible bulk-terminated surfaces by density functional theory (DFT) to investigate surface stability. The Ni2In3(100) surface was prepared by ion bombardment and annealing under ultrahigh vacuum conditions. We find that ion bombardment preferentially removes indium (In), while annealing promotes In segregation to the surface. After annealing, the surface exhibits root a (1 x 1) LEED pattern. The surface develops a three-domain c(2 3 x 4) rectangular structure upon exposure to ambient hydrogen present in the experimental chamber or hydrogen dosed from an external source, as evidenced by both STM and LEED. Both nickel (Ni) and In oxidize upon exposure to molecular oxygen. Based on STM and LEIS results along with surface energy calculations, we reveal that the surface planes contain In atoms bonded with Ni, the catalytically active constituent, suggesting that the surface may be stabilized by intermetallic bonding.

Ternary intermetallic silicides, germanides, and stannides of 4‐4‐7 stoichiometry are known to crystallize in the Zr 4 Co 4 Ge 7 ‐type structure of space group I4/mmm . A distinctive feature of this type of structure lies in the presence of short Si–Si, Ge–Ge, and Sn–Sn interatomic distances, close to the covalent bonding distances in the diamond‐type structures of silicon, germanium, and tin, which are thought to promote the emergence of remarkable physical properties. In this article, experimental and theoretical investigations performed on Zr 4 Mn 4 Si 7 are reported and discussed. It is shown that this compound, in its stoichiometric composition, crystallizes in an unprecedented crystal structure of space group P4/nmm , strongly related to the Zr 4 Co 4 Ge 7 ‐type. Theoretical calculations based on density functional theory and combined with the experimental results show that silicon deficiency in nominal composition and temperature are key parameters in its phase stability. Finally, magnetic measurements reveal a ferromagnetic‐like phase transition around 45 K.

While of significant value in supplying sustainable electricity for mobile and stationary use, the large-scale application of direct methanol fuel cells (DMFCs) is an ongoing challenge. DMFCs make use of methanol oxidation (MOR) on the anode and oxygen reduction (ORR) on the cathode, with the two reaction chambers being separated by an ion-conducting membrane. Broad application is hindered by material limitations due to sluggish kinetics on the anode, as the MOR involves six electrons, as well as limited temperature stability and methanol crossover of conventional membrane materials. Their temperature resistance also restricts the temperature in the fuel cell, which otherwise could be increased to overcome the kinetic limitations of the anode. As the large-scale application of DMFCs holds a high potential to contribute significantly to a sustainable energy infrastructure, the efforts and ideas in material development are reviewed to achieve highly active, durable, and stable anode catalysts as well as membrane materials, opening the temperature window up to 200 °C. This review reveals the advantageous catalytic properties of intermetallic catalysts as anode materials and lays out polybenzimidazoles as simple yet modular membrane materials.

Pd-based catalysts have been recognized to selectively hydrogenate acetylene to ethylene. Among them, the SnxGa1-xPd2 (0 <= x <= 1) ternary compound, formed from GaPd2 and SnPd2, shows intriguing catalytic performances. In this study, after identifying the (210) surface of GaPd2 and SnPd2 as the most stable ones, among the three orientations (010), (210), (013), we show that the preferred adsorption sites for both hydrogen and acetylene are surface Pd3 sites, consistent with previous findings on GaPd. For the same surface orientation, adsorbates are more strongly adsorbed on GaPd2 than on SnPd2, supporting the idea of a contrasted catalytic behavior between these two intermetallic compounds towards hydrogenation reactions. Our calculations reveal two regimes for H2 adsorption, depending on the Sn content (below or above 9 at.%), suggesting a connection with the optimal catalytic performances identified experimentally at 4% at. Sn. This study deepens our understanding of how metal substitution shapes the adsorption characteristics of SnxGa1-xPd2, unveiling new insights into the catalytic properties of intermetallic compounds.

It is well-known that in elemental metals, the onsite Coulomb energy of transition-metal (TM) d-electrons, Udd, is significantly smaller than Uff of f-electron rare-earth (RE) metals. Consequently, Udd is often neglected in RE-TM intermetallic alloys. In spite of the low value of Udd compared to Uff, we quantify and clarify the important role of Udd in partially filled d-bands of RE-TM alloys. We investigate the electronic structure of a typical RE-TM ferrimagnetic series Gd6(Mn1-xMx)23 (M = Fe, Co; x = 0.0, 0.3), which shows promising magnetocaloric properties. Resonant photoemission and constant initial state spectroscopy is used to identify the Mn 3d, Fe 3d, and Co 3d partial density of states (PDOS) in the valence band. The photon energy-dependent spectral evolution allows us to separate out the lower Hubbard band and the two-hole correlation satellites in the Mn, Fe, and Co 3d PDOS. Using the Cini-Sawatzky method, we determine an average Udd = 2.1 +/- 0.4 eV, 2.2 +/- 0.4 eV, and 2.9 +/- 0.4 eV for the Mn 3d, Fe 3d, and Co 3d states, respectively. The relatively larger Udd for Co compared to Fe 3d states results in lower DOS for the coherent feature at the Fermi level (EF) and higher DOS in the lower Hubbard band away from EF in Gd6(Mn0.7Co0.3)23 compared to Gd6(Mn0.7Fe0.3)23. To understand the role of Coulomb correlations on the electronic structure and magnetic properties, ab initio electronic structure calculations using density functional theory with onsite Coulomb correlations (DFT+U) were carried out for the parent Gd6Mn23. The results show that the calculated Mn magnetic moments are consistent with experiments Mn = 0.75 eV, corresponding to Udd = 1.65 eV and Jdd = 0.9 eV. Further, using the calculated Gd and Mn PDOS and known photoionization cross-sections, the simulated Gd6Mn23 spectrum is fairly consistent with the experimental valence band spectrum. The results indicate the crucial role of d-d correlations in the presence of large f-f correlations for tuning the electronic structure and magnetic properties of RE-TM intermetallics.

AbstractMany large unit-cell rare-earth transition metal ternary alloys of the type Ra(M1−xM’x)b exhibit non-monotonic ferrimagnetic Curie temperatures (TC) coupled to monotonic composition-controlled magnetization. Its origin remains an important long-standing puzzle in the absence of studies probing their temperature-dependent element-specific magnetism. Here, in order to resolve this issue and identify design principles for new R-M-M’ permanent magnets, we carry out x-ray magnetic circular dichroism (XMCD) for the series Gd6(Mn1−xFex)23, x = 0.0 − 0.75. The results show that the net Mn-moment reduces and switches from parallel to antiparallel for x ≥ 0.2, while the Fe-moment is always antiparallel to the Gd-moment. Kouvel-Fisher analyses of XMCD data reveals distinct sublattice TC’s and 3D Heisenberg criticality. Band structure calculations show magnetic moments and density of states consistent with experiments. The magnetic phase diagram shows three regions characterized by (i) Mn-sublattice bulk-TC > Gd-sublattice TC, (ii) a reduced common-TC for all sublattices, and (iii) Fe-sublattice bulk-TC > Gd-sublattice TC. The Mn-moment switching and gradual increase of Fe-moment combine to cause non-monotonic TC’s with monotonic magnetization. The study indicates the importance of element-specific TC’s for tuning magnetic properties.

The field of intermetallic catalysts, alloying a p-block and a transition metal to form a pM-TM bimetallic alloy, is experiencing robust growth, emerging as a vibrant frontier in catalysis research. Although such materials are increasingly used in the form of nanoparticles, a precise description of their atomic arrangements at the nanoscale remains scarce. Based on the In-Pd binary as a typical pM-TM system, we performed density functional theory calculations to investigate the morphologies, relative stabilities and electronic properties of 24 & Aring; and 36 & Aring; nanoparticles built from the In3Pd2, InPd and InPd3 compounds. Wulff equilibrium structures are compared to other ordered and disordered structures. Surface energies are computed to discuss their thermodynamic stability, while work functions are calculated to examine their electronic structures. For any compound, increasing the size leads to the stabilisation of Wulff polyhedra, which are found to offer smaller surface energies than non-crystalline and chemically disordered structures. Disordered In3Pd2 and InPd nanoparticles show a tendency towards amorphisation, owing to repulsive short In-In bonds. Tuning nanoparticles' work functions can be achieved through the control of the surface structure and composition, by virtue of the roughly linear correlation found between the surface composition and the work function which nevertheless includes a certain number of outliers. This work paves the way to rationalisation of both structural and electronic properties of pM-TM nanoparticles. The field of intermetallic catalysts, alloying a p-block and a transition metal to form a pM-TM bimetallic alloy, is experiencing robust growth, emerging as a vibrant frontier in catalysis research.

It is well-known that in elemental metals, the onsite Coulomb energy of transition-metal (TM) $d$-electrons, ${U}_{dd}$, is significantly smaller than ${U}_{ff}$ of $f$-electron rare-earth (RE) metals. Consequently, ${U}_{dd}$ is often neglected in RE-TM intermetallic alloys. In spite of the low value of ${U}_{dd}$ compared to ${U}_{ff}$, we quantify and clarify the important role of ${U}_{dd}$ in partially filled $d$-bands of RE-TM alloys. We investigate the electronic structure of a typical RE-TM ferrimagnetic series ${\mathrm{Gd}}_{6}{({\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{M}}_{x})}_{23}$ (M = Fe, Co; $x=0.0,0.3$), which shows promising magnetocaloric properties. Resonant photoemission and constant initial state spectroscopy is used to identify the Mn $3d$, Fe $3d$, and Co $3d$ partial density of states (PDOS) in the valence band. The photon energy-dependent spectral evolution allows us to separate out the lower Hubbard band and the two-hole correlation satellites in the Mn, Fe, and Co $3d$ PDOS. Using the Cini-Sawatzky method, we determine an average ${U}_{dd}=2.1\ifmmode\pm\else\textpm\fi{}0.4\phantom{\rule{0.16em}{0ex}}\mathrm{eV}, 2.2\ifmmode\pm\else\textpm\fi{}0.4\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$, and $2.9\ifmmode\pm\else\textpm\fi{}0.4\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$ for the Mn $3d$, Fe $3d$, and Co $3d$ states, respectively. The relatively larger ${U}_{dd}$ for Co compared to Fe $3d$ states results in lower DOS for the coherent feature at the Fermi level (${E}_{F}$) and higher DOS in the lower Hubbard band away from ${E}_{F}$ in ${\mathrm{Gd}}_{6}{({\mathrm{Mn}}_{0.7}{\mathrm{Co}}_{0.3})}_{23}$ compared to ${\mathrm{Gd}}_{6}{({\mathrm{Mn}}_{0.7}{\mathrm{Fe}}_{0.3})}_{23}$. To understand the role of Coulomb correlations on the electronic structure and magnetic properties, ab initio electronic structure calculations using density functional theory with onsite Coulomb correlations ($\mathrm{DFT}+U$) were carried out for the parent ${\mathrm{Gd}}_{6}{\mathrm{Mn}}_{23}$. The results show that the calculated Mn magnetic moments are consistent with experiments when ${U}_{\text{Mn}}^{\text{DFT}}=0.75\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$, corresponding to ${U}_{dd}=1.65\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$ and ${J}_{dd}=0.9\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$. Further, using the calculated Gd and Mn PDOS and known photoionization cross-sections, the simulated ${\mathrm{Gd}}_{6}{\mathrm{Mn}}_{23}$ spectrum is fairly consistent with the experimental valence band spectrum. The results indicate the crucial role of d-d correlations in the presence of large f-f correlations for tuning the electronic structure and magnetic properties of RE-TM intermetallics.

(root 3 x root 3)R30 honeycomb superstructure ultrathin Ce-Ti-O film was prepared and confirmed using scanning tunneling microscopy (STM) and low-energy electron diffraction. The structural model of (root 3 x root 3)R30 honeycomb superstructure ultrathin film is determined using ab initio calculation and photoelectron holography. In the density functional theory (DFT) calculations, the (root 3 x root 3)R30 honeycomb superstructural model was calculated in two different conditions. The photoelectron holograms of Ti2+ and Ti3+ were separated from Ti 2p photoelectron spectra of (root 3 x root 3)R30 honeycomb superstructure, using a display-type retarding field analyzer. From the different forward-focusing peaks on the photoelectron holograms of Ti2+ and Ti3+, the vertical height between Ti divalent atoms and O atoms is higher than that between Ti trivalent atoms and O atoms. Also, the distance and direction of O and Ce atoms above Ti could be found. As a result, the simulated photoelectron holograms and the simulated STM image of the calculated Ce-Ti-O honeycomb superstructural model agree with the experimental photoelectron holograms and the experimental STM images.

The atomic structure and electronic properties of the (100) surface of the Au-Si-Ho Tsai-type quasicrystalline approximant has been investigated under ultrahigh vacuum conditions. After annealing the sample between 853 K and 878 K, Au-Si-Ho(100) exhibits a (2 x 1) surface reconstruction with a topography described by large terraces separated by a single step height equal to half the unit-cell parameter. The surface appears to terminate at specific bulk planes intercepting the Tsai-type clusters at their center. The electronic density of states is dominated by the 5d states of Au below the Fermi level and by the 5d states of Ho above the Fermi level with a metalliclike Fermi edge.

Intermetallic compounds are promising materials in numerous fields, especially those involving surface interactions, such as catalysis. A key factor to investigate their surface properties lies in adsorption energy maps, typically built using first-principles approaches. However, exploring the adsorption energy landscapes of intermetallic compounds can be cumbersome, usually requiring huge computational resources. In this work, we propose an efficient method to predict adsorption energies, based on a Machine Learning (ML) scheme fed by a few Density Functional Theory (DFT) estimates performed on n sites selected through the Farthest Point Sampling (FPS) process. We detail its application on the Al13Co4(100) quasicrystalline approximant surface for several atomic adsorbates (H, O, and Pb). On this specific example, our approach is shown to outperform both simple interpolation strategies and the recent ML force field MACE [arXiv.2206.07697], especially when the number n is small, i.e., below 36 sites. The ground-truth DFT adsorption energies are much more correlated with the predicted FPS-ML estimates (Pearson R-factor of 0.71, 0.73, and 0.90 for H, O and Pb, respectively, when n = 36) than with interpolation-based or MACE-ML ones (Pearson R-factors of 0.43, 0.39, and 0.56 for H, O, and Pb, in the former case and 0.22, 0.35, and 0.63 in the latter case). The unbiased root-mean-square error (ubRMSE) is lower for FPS-ML than for interpolation-based and MACE-ML predictions (0.15, 0.17, and 0.17 eV, respectively, for hydrogen and 0.17, 0.25, and 0.22 eV for lead), except for oxygen (0.55, 0.47, and 0.46 eV) due to large surface relaxations in this case. We believe that these findings and the corresponding methodology can be extended to a wide range of systems, which will motivate the discovery of novel functional materials.

Steel is the most commonly manufactured material in the world. Its performances can be improved by hot-dip coating with the low weight aluminum metal. The structure of the Al parallel to Fe interface, which is known to contain a buffer layer made of complex intermetallic compounds such as Al5Fe2 and Al13Fe4, is crucial for the properties. On the basis of surface X-ray diffraction, combined with theoretical calculations, we derive in this work a consistent model at the atomic scale for the complex Al13Fe4(010) parallel to Al5Fe2(001) interface. The epitaxial relationships are found to be [130]Al5Fe2 parallel to[010]Al13Fe4 and [1 1 constrained energies, as well as works of adhesion, calculated for several structural models based on density functional theory, identify the lattice mismatch and the interfacial chemical composition as main factors for the stability of the interface. Molecular dynamics simulations suggest a mechanism of Al diffusion to explain the formation of the complex Al13Fe4 and Al5Fe2 phases at the Al parallel to Fe interface. KEYWORDS: surface X-ray diffraction, density functional theory, Al-Fe interface, adhesion, Al13Fe4, Al5Fe2 0]Al5Fe2 parallel to[100]Al13Fe4. Interfacial and

The intermetallic Al5Co2 is defined as a structurally complex material and is considered a low-order quasicrystalline approximant. A single crystal of Al5Co2(001) was obtained by the Czochralski method. The sample was characterized by X-ray photoelectron spectroscopy (XPS), low-energy electron diffraction (LEED), and X-ray photoelectron diffraction (PED). The surface composition was also analyzed by XPS, indicating only Al and Co compounds. In the current research, the crystal structure was qualitatively analyzed using the LEED patterns for different incident beam energies indicating a (1 × 1) termination, also in accordance with some literature works. The structure study was performed by applying the standard software MSCD and showed a (1 × 1) pattern. In addition, four different termination models for this termination were tested. The reliability factor indicated that the best termination belongs to the Al-rich surface layer.

A method for subsurface visualization and characterization of hidden subsurface nano-structures based on scanning tunelling microscopy/spectroscopy (STM/STS) has been developed. Nano-objects buried under a metal surface up to several tens of nanometers can be visualized through the metal surface and characterized with STM without destroying the sample. This non-destructive method exploits quantum well (QW) states formed by partial electron confinement between the surface and buried nano-objects. The specificity of STM allows for nano-objects to be singled out and easily accessed. Their burial depth can be determined by analysing the oscillatory behaviour of the electron density at the surface of the sample, while the spatial distribution of electron density can give additional information about their size and shape. The proof of concept was demonstrated with different materials such as Cu, Fe, and W in which the nanoclusters of Ar, H, Fe and Co were buried. For each material, the maximal depth of subsurface visualisation is determined by the material parameters and ranges from several nanometers to several tens of nanometers. To demonstrate the ultimate depth of subsurface STM-vision as the principal limit of our approach, the system of Ar nanoclusters embedded into a single-crystalline Cu(110) matrix has been chosen since it represents the best combination of the mean free path, smooth interface and inner electron focusing. With this system we experimentally demonstrated that Ar nanoclusters of several nanometers large buried as deep as 80 nm can still be detected, characterized and imaged. The ultimate depth of this ability is estimated to be 110 nm. This approach using QW states paves the way for enhanced 3D characterization of nanostructures hidden well below a metallic surface.

Monometallic platinum and nickel nanoparticles and platinum-nickel nanoalloys are examined in the range 13-976 atoms from density functional theory calculations. A large set of competitive symmetries and morphologies are considered including the usual Mackay icosahedral, Marks decahedral, and truncated octahedral forms. A comparative analysis of relative stability order is addressed on the basis of four stability descriptors all predicted at the ab initio level from spin-polarized calculations including van der Waals interactions. For platinum nanoparticles, they unanimously conclude on the preference of truncated octahedral morphology in the range of 147-201 atoms. For nickel and platinum-nickel nanoclusters, three descriptors (cohesion energy, nanoparticle surface energy, and vibrational band center) also support such octahedral symmetry (with a skin-heart chemical ordering for nanoalloys), whereas the excess energy rather favors the icosahedral morphology (with multishell and core-shell arrangement). Such discrepancies feed the debate related to the impact of normalization on the predictive power of these descriptors and recall the high importance of validating theoretical models from a quantitative standpoint. This work invites the experimentalists to synthesize, characterize, and measure surface energetics of PtNi nanolloys in highly controlled operating conditions.