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[Display omitted] Machine learning (ML) models utilizing structure-based features provide an efficient means for accurate property predictions across diverse chemical spaces. However, obtaining equilibrium crystal structures typically requires expensive density functional theory (DFT) calculations, which limits ML-based exploration to either known crystals or a small number of hypothetical crystals. Here, we demonstrate that the application of Bayesian optimization with symmetry constraints using a graph deep learning energy model can be used to perform "DFT-free" relaxations of crystal structures. Using this approach to significantly improve the accuracy of ML-predicted formation energies and elastic moduli of hypothetical crystals, two novel ultra-incompressible hard MoWC 2 (P 6 3 / mmc) and ReWB (Pca 2 1 ) were identified and successfully synthesized via in situ reactive spark plasma sintering from screening 399,960 transition metal borides and carbides. This work addresses a critical bottleneck to accurate property predictions for hypothetical materials, paving the way to ML-accelerated discovery of new materials with exceptional properties. [ABSTRACT FROM AUTHOR]

The crystal structure and composition of the zeta phase in the group VB transition metal carbides are not completely understood despite decades of experimental studies. As such, the phase rarely appears on phase diagrams of the group VB transition metal carbides. There is currently renewed interest in this phase, as tantalum carbide composites exhibit high fracture toughness in the presence of this phase. This work extends the initial computational study using density functional theory of the phase stability of the zeta phase in the tantalum carbide system, where the tantalum carbide zeta‐phase crystal structure and stability were determined, to the niobium and vanadium carbides. It is shown that the zeta phases in the three systems share the same crystal structure and it is an equilibrium phase at low temperatures. The carbon atom ordering in the three different phases is explored and it is demonstrated that the zeta phase in the tantalum carbides prefers to order carbon atoms differently than in the niobium and vanadium carbide zeta phases. Finally, the properties of this crystal are computed, including elastic constants, electronic densities of states and phonon dispersion curves, to illustrate that this crystal structure is similar to other transition metal carbides. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Interstitial transition metal nitrides and carbides based on simple crystal structures with partial occupation of certain sites by N and C frequently show long-range ordering. In this work the focus is on the important group of superstructures based on a face-centered cubic (fcc)-based arrangement of the metal atoms and octahedral site occupation by N or C. The ordering tendencies are explored for various Ni 4 N and Ni 4 C superstructures using density-functional-theory. The ordering tendencies differ strikingly as revealed by the low-energy superstructures encountered for Ni 4 N and for Ni 4 C: in the case of Ni 4 N 2nd-next-neighbor N-N pairs appear favorable whereas in Ni 4 C 1st-next neighbor C-C pairs are preferred. This can be explained by an interplay between elastic interactions favoring 1st-next neighbor pairs of N and C atoms in an fcc-based arrangement of metal atoms and chemical/Coulomb interactions favoring 2nd-next neighbor (i.e. more distant) pairs. While the elastic interactions are expected to be similar for N and C, the chemical/Coulomb interactions are stronger for N-N as compared to C-C and are thus able to explain the different ordering tendencies. [ABSTRACT FROM AUTHOR]

Transition metal carbides (TMC) have intriguing physical and chemical properties, especially when structured down to nanoscale. The temperature and chemical resilience of this family of materials made it ideal candidate for electrochemical applications in harsh environment. Among the TMC family, molybdenum carbide has been demonstrated as efficient catalyst for hydrogen evolution reactions (HER). This paper will use density function theory to investigate of the efficiency of molybdenum and tungsten carbide as catalyst for HER in neutral and alkane environment. [ABSTRACT FROM AUTHOR]

Transition metal carbides (TMC) have intriguing physical and chemical properties, especially when structured down to nanoscale. The temperature and chemical resilience of this family of materials made it ideal candidate for electrochemical applications in harsh environment. Among the TMC family, molybdenum carbide has been demonstrated as efficient catalyst for hydrogen evolution reactions (HER). This paper will use density function theory to investigate of the efficiency of molybdenum and tungsten carbide as catalyst for HER in neutral and alkane environment. [ABSTRACT FROM AUTHOR]

Refractory transition metal carbides have intriguing physical and chemical properties, especially when structured down to nanoscale. The lack of study in defected transition metal carbides, is partially due to the synthesis difficulty of refractory materials. The synthesis of defected carbide and their substitutional alloy will be even more difficult than single phase. First principle theory-based simulation can help to conceptualize the effects of substitutional defects on their mechanical properties. In this paper, we performed density functional theory (DFT) simulation of carbon defected α-MoC(1-x) phases to investigate their formation and mechanical properties for thesis sub-stoichio- metric materials. [ABSTRACT FROM AUTHOR]

First-principles calculations based on density functional theory was performed to analyse the structural stability of transition metal carbides TMC (TM = Ru, Rh, Pd, Os, Ir, Pt). It is observed that zinc-blende phase is the most stable one for these carbides. Pressure-induced structural phase transition from zinc blende to NiAs phase is predicted at the pressures of 248.5 GPa, 127 GPa and 142 GPa for OsC, IrC and PtC, respectively. The electronic structure reveals that RuC exhibits a semiconducting behaviour with an energy gap of 0.7056 eV. The high bulk modulus values of these carbides indicate that these metal carbides are super hard materials. The high B/G value predicts that the carbides are ductile in their most stable phase. [ABSTRACT FROM AUTHOR]

The development of novel transition metal carbides for improved hard coating technologies requires a detailed understanding of the factors influencing their stability and mechanical performance. To this end, we carried out first principles calculations based on density functional theory to tabulate the electronic structures, formation energies, and phonon dispersion curves of 3d transition metal carbides adopting zincblende, rocksalt, and cesium chloride structures. By analyzing the corresponding results, we outline a theoretical framework that describes how valence electron concentration and bonding configuration control the stability of these compounds. Many early transition metal carbides are predicted to be stable in the rocksalt and zincblende structures, enabled by filled bonding states, whereas the cesium chloride structure shows persistent instability. For compounds that are predicted to be stable, mechanical properties were investigated through calculation of elastic tensors, from which observable properties including Vicker's hardness and ductility were derived. A robust mechanical performance is shown to be correlated with complete filling of bonding orbitals as illustrated for rocksalt TiC and VC, which have calculated hardnesses of 25.66 and 22.63 GPa respectively. However, enhanced ductility and toughness can be achieved by allowing partial occupation of the antibonding states as in CrC, which has a relatively low Pugh's ratio of 0.51. [Display omitted] • Early 3d transition metal carbides show robust stability and high hardness. • Complete filling of bonding orbitals is crucial to maintain stability. • Partial antibonding contributes to decreased hardness but enhanced ductility. • Overoccupied antibonding orbitals cause instabilities in the rocksalt structure. • Jahn-Teller distortions cause instabilities in the zincblende structure. [ABSTRACT FROM AUTHOR]