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Intermetallic titanium aluminides, leveraging the ordered γ-TiAl phase, attract increasing attention in aerospace and automotive engineering due to their favorable mechanical properties at high temperatures. Of particular interest are γ-TiAl-based alloys with a Niobium (Nb) concentration of 5–10 at.%. It is a key question how to model such ternary alloys at the atomic scale with molecular dynamics (MD) simulations to better understand (and subsequently optimize) the alloys. Here, we present a comparative analysis of ternary TiAlNb interatomic potentials developed by the moment tensor potential (MTP) and deep potential molecular dynamics (DeePMD) methods specifically for the above mentioned critical Nb concentration range. We introduce a novel dataset (TiAlNb dataset) for potential training that establishes a benchmark for the assessment of TiAlNb potentials. The potentials were evaluated through rigorous error analysis and performance metrics, alongside calculations of material properties such as elastic constants, equilibrium volume, and lattice constant. Additionally, we explore finite temperature properties including specific heat and thermal expansion with both potentials. Mechanical behaviors, such as uniaxial tension and the calculation of generalized stacking fault energy, are analyzed to determine the impact of Nb alloying in TiAl-based alloys. Our results indicate that Nb alloying generally enhances the ductility of TiAl-based alloys at the expense of reduced strength, with the notable exception of simulations using DeePMD for the γ-TiAl phase, where this trend does not apply. [ABSTRACT FROM AUTHOR]

As early as 1975, Pitzer suggested that copernicium, flerovium, and oganesson are volatile substances behaving like noble gas because of their closed-shell configurations and accompanying relativistic effects. It is, however, precarious to predict the chemical bonding and physical behavior of a solid by knowledge of its atomic or molecular properties only. Copernicium and oganesson have been analyzed very recently by our group. Both are predicted to be semiconductors and volatile substances with rather low melting and boiling points, which may justify a comparison with the noble gas elements. Here, we study closed-shell flerovium in detail to predict its solid-state properties, including the melting point, by decomposing the total energy into many-body forces derived from relativistic coupled-cluster theory and from density functional theory. The convergence of such a decomposition for flerovium is critically analyzed, and the problem of using density functional theory is highlighted. We predict that flerovium in many ways does not behave like a typical noble gas element despite its closed-shell 7 p 1 / 2 2 configuration and resulting weak interactions. Unlike the case of noble gases, the many-body expansion in terms of the interaction energy does not converge smoothly. This makes the accurate prediction of phase transitions very difficult. Nevertheless, a first prediction by Monte Carlo simulation estimates the melting point at 284 ± 50 K. Furthermore, calculations for the electronic bandgap suggests that flerovium is a semiconductor similar to copernicium. [ABSTRACT FROM AUTHOR]

Five new mononuclear ruthenium(II) tris-ligated complexes have been synthesised, varying through the choice of azine in the family of 3-azinyl-4-(4-methylphenyl)-5-phenyl-4H-1,2,4-triazole ligands (Lazine): [Ru(Lpyridine)](PF6)2 (1), [Ru(Lpyridazine)](PF6)2 (2), [Ru(L4-pyrimidine)](PF6)2 (3), [Ru(Lpyrazine)](PF6)2 (4), [Ru(L2-pyrimidine)](PF6)2 (5). Three of them, 1·2MeCN·Et2O, 3·2MeCN·Et2O and 4·2MeCN, have been structurally characterised, confirming the presence of the meridional isomer, as was previously reported for the FeII analogues. Cyclic voltammetry studies, in dry CH3CN vs. Ag/0.01 M AgNO3, show that all five RuII complexes undergo a reversible RuIII/RuII process, with the midpoint potential (Em) increasing from 0.87 to 1.18 V as the azine is changed: pyridine < pyridazine < 2-pyrimidine < 4-pyrimidine < pyrazine. A strong inverse linear correlation (R2 = 0.98) is found between the RuIII/RuII redox potential and the calculated HOMO orbital energies, which is consistent with the expectation that it is easier to oxidise (lower Em) a metal ion with a higher HOMO orbital energy. The same trend was reported earlier for the family of analogous FeII complexes, albeit at lower values of Em in all cases. In addition, the ionisation potentials of the RuII complexes, as well as those of the other group 8 analogues (FeII and OsII), showed a linear relationship with Epa. As the MIII/II redox potentials of a family of complexes has been previously reported to correlate with ligand pKa values, a computational protocol to calculate, in silico, the pKa of the Lazine family of ligands was developed. A strong linear relationship was found between the readily calculated pKa of the Lazine ligand and the Epa of the MII complex, for all three families of complexes (R2 = 0.98). [ABSTRACT FROM AUTHOR]

Why the Group 1 elements crystallize in the body‐centered cubic (bcc) structure, and the iso‐electronic Group 11 elements in the face‐centered cubic (fcc) structure, remains a mystery. Here we show that a delicate interplay between many‐body effects, vibrational contributions and dispersion interactions obtained from relativistic density functional theory offers an answer to this long‐standing controversy. It also sheds light on the Periodic Table of Crystal Structures. A smooth diffusionless transition through cuboidal lattices gives a detailed insight into the bcc→fcc phase transition for the Groups 1 and 11 elements. [ABSTRACT FROM AUTHOR]

Bisher war es ein Rätsel, weshalb die Elemente der Gruppe 1 in der kubisch‐raumzentrierten (bcc) und die iso‐elektronischen Elemente der Gruppe 11 in der kubisch‐flächenzentrierten Struktur (fcc) kristallisieren. In dieser Untersuchung auf Grundlage von relativistischer Dichtefunktionaltheorie wird demonstriert, wie ein komplexes Zusammenspiel zwischen Mehrteilcheneffekten, Schwingungsenergiebeiträgen und Dispersionswechselwirkungen eine Antwort auf diese langjährige Kontroverse liefert und dabei gleichzeitig zum Verständnis des Periodensystems der Kristallstrukturen beiträgt. Ein sanfter, diffusionloser Übergang durch kuboidale Gitterstrukturen hindurch bietet detaillierte Einblicke in den bcc→fcc Phasenübergang für die Elemente der Gruppen 1 und 11. [ABSTRACT FROM AUTHOR]

The inevitable formation of passivating oxide films on the surface of the TiFe intermetallic compound limits its performance as a stationary hydrogen storage material. Extensive experimental efforts have been dedicated to the activation of TiFe, i.e. oxide layer removal prior to utilization for hydrogen storage. However, development of an efficient activation protocol necessitates a fundamental understanding of the composition and structure of the air-exposed surface and its interaction with hydrogen, which is currently absent. Therefore, in this study we explored the growth and nature of oxide films on the most exposed TiFe surface (110) in depth using static and dynamic first-principles methods. We identified the lowest energy structures for six oxygen coverages up to approximately 1.12 nm of thickness with a global optimization method and studied the temperature effects and structural evolution of the oxide phases in detail via ab initio molecular dynamics (AIMD). Based on structural similarity and coordination analysis, motifs for TiO2 and TiFeO3 as well as Ti(FeO2)x (x = 2, 3 or 5) phases were identified. On evaluating the interaction of the oxidized surface with hydrogen, a minimal energy barrier of 0.172 eV was predicted for H2 dissociation while H migration from the top of the oxidized surface to the bulk TiFe was limited by several high-lying energy barriers above 1.4 eV. Our mechanistic insights will prove themselves valuable for informed designs towards new activation methods of TiFe and related systems as hydrogen storage materials. [ABSTRACT FROM AUTHOR]

The effect of para‐substituent X on the electronic structure of sixteen tridentate 4‐X‐(2,6‐di(pyrazol‐1‐yl))‐pyridine (bppX) ligands and the corresponding solution spin crossover [FeII(bppX)2]2+ complexes is analysed further, to supply quantitative insights into the effect of X on the σ‐donor and π‐acceptor character of the Fe‐NA(pyridine) bonds. EDA‐NOCV on the sixteen LS complexes revealed that neither ΔEorb,σ+π (R2=0.48) nor ΔEorb,π (R2=0.31) correlated with the experimental solution T1/2 values (which are expected to reflect the ligand field imposed on the iron centre), but that ΔEorb,σ correlates well (R2=0.82) and implies that as X changes from EDG→EWG (Electron Donating to Withdrawing Group), the ligand becomes a better σ‐donor. This counter‐intuitive result was further probed by Mulliken analysis of the NA atomic orbitals: NA(px) involved in the Fe−N σ‐bond vs. the perpendicular NA(pz) employed in the ligand aromatic π‐system. As X changes EDG→EWG, the electron population on NA(pz) decreases, making it a better π‐acceptor, whilst that in NA(px) increases, making it a better σ‐bond donor; both increase ligand field, and T1/2 as observed. In 2016, Halcrow, Deeth and co‐workers proposed an intuitively reasonable explanation of the effect of the para‐X substituents on the T1/2 values in this family of complexes, consistent with the calculated MO energy levels, that M→L π‐backdonation dominates in these M−L bonds. Here the quantitative EDA‐NOCV analysis of the M−L bond contributions provides a more complete, coherent and detailed picture of the relative impact of M−L σ‐versus π‐bonding in determining the observed T1/2, refining the earlier interpretation and revealing the importance of the σ‐bonding. Furthermore, our results are in perfect agreement with the ΔE(HS‐LS) vs. σp+(X) correlation reported in their work. [ABSTRACT FROM AUTHOR]

Positron emission tomographic (PET) [Mathematical Expression Omitted] measurements of resting-state regional cerebral blood flow (CBF) were obtained in 29 right-handed men, 10 of whom stuttered and 19 of whom did not. PET images were analyzed by sampling 74 regions of interest (ROIs), 37 per hemisphere. ROI placement was guided both physiologically and anatomically. Physiological ROI placement was based on speech motor activations. Anatomical ROIs were positioned by reference to a stereotactic, neurosurgical atlas with positions confirmed and finely adjusted by co-registered magnetic-resonance images (MRIs). For all subjects, PET and MR images were normal to visual inspection. Highly significant (p < 0.0001) between-region and between-hemisphere effects were found for both groups, as have been previously reported for normal subjects, but no significant between-group differences were found for any regional CBF values. Analysis by a laterality index found a weakly significant between-groups effect (p = 0.04) that was isolated to five regions, four of which are implicated in speech or hearing. However, these regional laterality effects showed no consistent directionality, nor did these regions have absolute differences in regional blood flow between groups. Present findings do not support recent suggestions that developmental stuttering is associated with abnormalities of brain blood flow at rest. Rather, our findings indicate an essentially normal functional brain terrain with a small number of minor differences in hemispheric symmetry. KEY WORDS: stuttering, PET (positron emission tomography), functional-lesion