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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]

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]

Oganesson (Og) is the last entry into the Periodic Table completing the seventh period of elements and group 18 of the noble gases. Only five atoms of Og have been successfully produced in nuclear collision experiments, with an estimate half‐life for 294118 Og of 0.69+0.64-0.22 ms.[1] With such a short lifetime, chemical and physical properties inevitably have to come from accurate relativistic quantum theory. Here, we employ two complementary computational approaches, namely parallel tempering Monte‐Carlo (PTMC) simulations and first‐principles thermodynamic integration (TI), both calibrated against a highly accurate coupled‐cluster reference to pin‐down the melting and boiling points of this super‐heavy element. In excellent agreement, these approaches show Og to be a solid at ambient conditions with a melting point of ≈325 K. In contrast, calculations in the nonrelativistic limit reveal a melting point for Og of 220 K, suggesting a gaseous state as expected for a typical noble gas element. Accordingly, relativistic effects shift the solid‐to‐liquid phase transition by about 100 K. [ABSTRACT FROM AUTHOR]

Oganesson (Og) is the most recent addition to Group 18. Investigations of its atomic electronic structure have unraveled a tremendous impact of relativistic effects, raising the question whether the heaviest noble gas lives up to its position in the periodic table. To address the issue, we explore the electronic structure of bulk Og by means of relativistic Kohn–Sham density functional theory and many‐body perturbation theory in the form of the GW method. Calculating the band structure of the noble‐gas solids from Ne to Og, we demonstrate excellent agreement for the band gaps of the experimentally known solids from Ne to Xe and provide values of 7.1 eV and 1.5 eV for the unknown solids of Rn and Og. While this is in line with periodic trends for Rn, the band gap of Og completely breaks with these trends. The surprisingly small band gap of Og moreover means that, in stark contrast to all other noble‐gas solids, the solid form of Og is a semiconductor. [ABSTRACT FROM AUTHOR]

Quantum chemical calculations using density functional theory at the BP86‐D3(BJ)/def2‐TZVPP level of theory are reported for transition metal compounds [TM]‐L in high and low oxidation states involving carbene, carbyne, alkene, and alkyne ligands L. The nature of the [TM]‐L bond is analyzed with the energy decomposition analysis ‐ natural orbitals for chemical valence (EDA‐NOCV) method. The calculations reveal that transition metal compounds with ligands, that are typically classified as donor–acceptor complexes possessing dative bonds (Fischer‐type carbenes and carbynes, alkene, and alkyne complexes) or as TM compounds with electron‐sharing bonds (Schrock‐type carbenes and carbynes, metallacyclopropanes, and metallacyclopropenes), exhibit significant differences between the orbital interactions when closed‐shell or open shell fragments are used. Fischer‐type carbene complexes have much lower orbital interaction (ΔEorb) values when singlet fragments are employed compared to triplet fragments. In contrast, singlet and triplet fragments of Schrock‐type carbene complexes give similar ΔEorb values. The best description for Fischer‐type carbyne complexes is found for neutral fragments in their electronic doublet state, which engage in a mixture of dative bonding (σ donation and π backdonation) and one electron‐sharing π bond. The EDA‐NOCV calculations of Schrock‐type carbynes using open‐shell species in their quartet electronic state give similar ΔEorb values as neutral fragments in their electronic doublet state. Alkene and alkyne complexes, but also metallacyclic species, are best described with singlet fragments, but the difference between the ΔEorb values for dative bonding and electron‐sharing bonding using triplet fragments becomes much smaller for molecules that are considered as metallacycles. © 2018 Wiley Periodicals, Inc. EDA‐NOCV calculations are employed to distinguish between electron sharing and dative interactions in transition metal–ligand bonds and to visualize the associated pairwise orbital interactions. [ABSTRACT FROM AUTHOR]

Heterometalldotierte Goldcluster sind durch nasschemische Synthese schwer zugänglich, und mit Hauptgruppenmetallen oder frühen Übergangsmetallen dotierte Cluster sind rar. Die Verbindungen [M(AuPMe3)11(AuCl)]3+ (M=Pt, Pd, Ni) ( 1- 3), [Ni(AuPPh3)(8-2 n)(AuCl)3(AlCp*) n] ( n=1, 2) ( 4, 5) und [Mo(AuPMe3)8(GaCl2)3(GaCl)]+ ( 6) wurden selektiv durch Transmetallierung von [M(M′Cp*) n] (M=Mo, E=Ga, n=6; M=Pt, Pd, Ni, M′=Ga, Al; n=4) mit [ClAuPR3] (R=Me, Ph) hergestellt und mit Einkristallröntgenbeugung sowie ESI-MS charakterisiert. Mithilfe von DFT-Rechnungen wurden die Bindungsverhältnisse analysiert. Die Transmetallierung ist eine wirkungsvolle Syntheseroute hin zu heterometalldotierten Goldclustern, deren Aufbau der 18-Valenzelektronenregel für das Zentralmetallatom gehorcht und die mit dem Superatomkonzept auf Grundlage des Jellium-Modells übereinstimmen. [ABSTRACT FROM AUTHOR]

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FeTi-based hydrides have recently re-attracted attention as stationary hydrogen storage materials due to favorable reversibility, good sorption kinetics and relatively low costs compared to alternative intermetallic hydrides. Employing the OpenCalphad software, the thermodynamics of the (FeTi) 1 − x H x (0 ≤ x ≤ 1) system were assessed as a key basis for modeling hydrogenation of FeTi-based alloys. New thermodynamic data were acquired from our experimental pressure-composition-isotherm (PCI) curves, as well as first-principles calculations utilizing density functional theory (DFT). The thermodynamic phase models were carefully selected based on critical analysis of literature information and ab-initio investigations. Key thermodynamic properties such as dissociation pressure, formation enthalpies and phase diagrams were calculated in good agreement to our performed experiments and literature-reported data. This work provides an initial perspective, which can be extended to account for higher-order thermodynamic assessments and subsequently enables the design of novel FeTi-based hydrides. In addition, the assessed thermodynamic data can serve as key inputs for kinetic models and hydride microstructure simulations. [Display omitted] • Calphad modeling of the FeTi-H system's phases and hydrides formation enthalpy. • Faithful description of the FeTi-H paraequilibrium and phase diagram. • Combination of new experimental data and first-principles calculations. • Thermodynamic assessment using the OpenCalphad software. • Calculation of pressure-composition-isotherm curves of the FeTi-H system. [ABSTRACT FROM AUTHOR]

The underlying physico-chemical interactions between transition metal-based boride particles that formed during the dehydrogenation process and MgB 2 in 2LiBH 4 +MgH 2 reactive hydride composite at the atomic scale are still unknown. In this work, the properties of the TiB 2 /MgB 2 interface were investigated by first-principles calculations utilizing density functional theory (DFT). Taking the two terminations of both MgB 2 and TiB 2 as well as four different stacking sequences into account, energies of the TiB 2 and MgB 2 (0001) surfaces as well as the work of adhesion and the electronic structure of the interfaces were studied. The results show that the interface between the B-terminated MgB 2 (0001) surface and the Ti-terminated TiB 2 (0001) surface is the energetically most favorable among all four stacking options and possesses the largest work of adhesion. Our results further show that the TiB 2 particles possess good nucleation potency for MgB 2 particles from the thermodynamic perspective. [Display omitted] [ABSTRACT FROM AUTHOR]

Interstitial metal hydrides (MHs) have attracted considerable attention in the field of hydrogen technology, particularly in the context of storage and compression applications. Because of their minor hysteresis effects, good cyclability, activation simplicity, and high volumetric storage density, LaNi 5 -based alloys are recognized as prominent candidates for hydrogen storage application. Additionally, the system's thermodynamic and electrochemical properties can be modified to suit the requirements of a particular application by alloying specific substituents. To ascertain the thermodynamic effects of Ce addition within LaNi 5 , in this work the Ce H and CeNi 5 H systems have been modeled with the CALPHAD method. For this reason, in this work, two different thermodynamic models have been developed and assessed using the same pressure-composition isotherms (PCIs) datasets obtained from literature and theoretical formation energies newly calculated employing periodic density functional theory (DFT). Direct comparison of the models against each other in terms of accuracy and physical plausibility revealed that extrapolation of thermodynamic properties to data-scarce regions is more reasonable with fewer model parameters and in agreement with other similar systems within the rare-earth (RE) metal-hydride class. In addition, the CeNi 5 H system was investigated by assessing the (Ce)(Ni) 5 (V a,H) 7 phase model, which could accurately predict hydrogen storage properties while being compatible with previously developed LaNi 5 H models. Ultimately, the models developed in this study may be employed and extended to describe multi-component RE H systems and allow for thermodynamic computations that are highly desirable for accurate predictions of hydrogen absorption/desorption properties and degradation characteristics within the (La,Ce)Ni 5 H metal hydride family. [ABSTRACT FROM AUTHOR]

Organozinc (ZnR with R = Cp*, Me, CI, Br) ligated transition metal (M) half-sandwich compounds of general formula [Cp*M(ZnR)5] (M = Fe, Ru) are presented in this work. The new compounds were obtained by treatment of various GaCp* ligated precursors with suitable amounts of ZnMe2 to exchange Ga against Zn. This exchange follows a strict Ga:Zn ratio of 1:2. Accordingly, a Ga/Zn mixed compound [{Cp*Ru(GaCp*)(ZnCp*)(ZnCl)2}2] can be obtained if the amount of ZnMe2 is reduced so that one GaCp* remains coordinated to the transition metal. All new compounds were characterized by elemental analysis, ¹H and 13C NMR spectroscopy as well as by single crystal X-ray diffraction techniques, if applicable. The coordination polyhedra of [Cp*M(ZnR)5] can be derived from the pseudo homoleptic parent compound [Ru(ZnCp*)4(ZnMe),6], as emphasized by continuous shape measures analysis (CShM). Computational investigations at the density functional theory (DFT) level of theory were performed, revealing no significant attractive interaction of the zinc atoms and therefore these compounds are best described as classical complexes, rather than cluster compounds. The Ru-L bond strength follow the order Cp* > ZnCl > ZnMe > ZnCp*. [ABSTRACT FROM AUTHOR]