Search

Hydrogen-abundant compounds, as highly potential candidates of near- or room-temperature superconductors, have recently attracted substantial attention. It is noted that metal-rich hydrides may exhibit unique electride feature, together with potential superconductivity, which indicates that they could be regarded as electride superconductor (ESC) hydrides. Herein, we performed the first-principles structure searches of calcium-rich hydrides for designing ESC hydrides. Strikingly, unprecedented calcium-based hydride Ca2H with robust stability and excellent metallicity is identified under compression, where it possesses the zero-dimensional distribution feature of interstitial electrons serving as interstitial quasiatoms (ISQs), mainly originating from the donation of calcium atoms. Interestingly, cubic Fm3¯m Ca2H, with antifluorite-type configuration, consists of a host Ca sublattice and guests H and ISQs confined in the center of Ca8 cubes. Furthermore, Ca2H is predicted to have a superconducting critical temperature Tc of 6 K at 100 GPa and exhibit significantly enhanced superconductivity up to 11 K when dynamically stabilized to 30 GPa, which is predominantly attributed to the remarkable softening of low-frequency acoustic phonon modes involving Ca-dominated vibrations, accompanied by the strong coupling with Ca 3d states near the Fermi energy. Additionally, the yielded electride Na2H via substituting Ca with Na in Ca2H is found to have a notably high Tc of 46 K at 30 GPa. Our current work improved the understanding of structures and properties of electrides, as well as paving the way for exploring emergent ESCs in hydride systems. [ABSTRACT FROM AUTHOR]

The pressure-induced reaction between xenon (Xe) and other non-inert gas elements and the resultant crystal structures have attracted great interest. In this work, we carried out extensive simulations on the crystal structures of Xe–alkali metal (Xe–AM) systems under high pressures. Among all predicted compounds, KXe and RbXe are found to become stable at a pressure of ∼16 GPa by adopting a cubic symmetry of space group Pm3¯m. The stabilization of KXe and RbXe requires slightly lower pressure compared with that of previously reported CsXe (25 GPa), interestingly, which is in contrast to the electronegativity order of the AMs and unexpected. Our simulations also indicate that all predicted Xe compounds contain negatively charged Xe. Moreover, our in-depth analysis indicates that the occupation of AM d-orbitals plays a critical role in stabilizing these Xe-bearing compounds. These results shed light on the understanding of the reaction between Xe and AMs and the formation mechanism of the resultant crystal structures. [ABSTRACT FROM AUTHOR]

Because of the particular characteristics of layered materials, searching for new two-dimensional (2D) structures has become the foundation of future device manufacture. Using first-principles calculations and theoretical analysis, we identified a new monolayer B2O and systematically investigated its fundamental mechanical and electronic properties, especially under strain. Due to the complicated puckered hinge structure of monolayer B2O, it possesses an intrinsic negative Poisson's ratio of −0.021. Moreover, we found that the superconducting state of monolayer B2O can be improved, where strain plays an effective role in regulating the properties of the 2D material. The current results elucidate the structure and corresponding properties of monolayer B2O, which may stimulate related fundamental research and potential nanoscale applications. [ABSTRACT FROM AUTHOR]

In addition to the known Au3+ and Au5+, it has recently been shown that Au is likely to possess unusual valence states in compressed Au–F compounds. However, our simulations reveal that polymeric ground-state AuF4 shows an unexpected 6-fold coordination rather than a 4-fold one, indicating that more complete comprehending on the anomalous Au4+ is highly required. To fully understand the nature and origin of anomalous valence states in Au, we have extensively investigated the ground-state structures of Au–F compounds at high pressures using quantum mechanical computational methods. As a consequence, we identify several previously unreported (stable) AuF2, AuF3 and AuF4 structures. Our results extend the known polymorphism of AuFn compounds and offer a fundamental understanding of the origin of unusual valence states in Au that prevail at high pressure. [ABSTRACT FROM AUTHOR]

Transition metal dichalcogenides have attracted significant attention due to both fundamental interest and their potential applications. Here, we have systematically explored the crystal structures of ReX2 (X = S, Se, and Te) over the pressure range of 0–300 GPa, employing swarm-intelligence-based structure prediction methodology. Several new structures are found to be stable at high pressures. The calculated enthalpy of formation suggested that all predicted high-pressure structures are stable against decomposition into elemental end-members. Moreover, we found that the simulated X-ray diffraction patterns of ReSe2 are in good agreement with experimental data. Pressure-induced metallization of ReX2 has been revealed from the analysis of its electronic structure. Our electron–phonon coupling calculations indicate ReSe2 and ReTe2 are superconducting phases at high pressures. [ABSTRACT FROM AUTHOR]

Carbon has the capability of forming various bonding states that affect the structures and properties of transition metal carbides. In this work, structural search was performed to explore the structural diversity of LaC2 at pressures of 0.0–30.0 GPa. Five stable structures of LaC2 reveal a variety of carbon structural units ranging from a dimer to bent C3, zigzag C4 and armchair polymer chains. A series of pressure-induced structural transformations are predicted, I4/mmm (i.e. experimental α phase) →C2/c→Pnma→Pmma, which involve the catenation of carbon from a dimer to zigzag C4 units and further to armchair polymer chains. The bent C3 unit appears in a novel Immm structure. This structure is the theoretical ground state of LaC2 under ambient conditions, but is kinetically inaccessible from the experimental α phase. LaC2 becomes thermodynamically metastable relative to La2C3 + diamond above 17.1 GPa, and eventually decomposes into constituent elements above 35.6 GPa. The presented results indicate that catenation of carbon can be realized even in simple inorganic compounds under nonambient conditions. [ABSTRACT FROM AUTHOR]

Because of the particular characteristics of layered materials, searching for new two-dimensional (2D) structures has become the foundation of future device manufacture. Using first-principles calculations and theoretical analysis, we identified a new monolayer B2O and systematically investigated its fundamental mechanical and electronic properties, especially under strain. Due to the complicated puckered hinge structure of monolayer B2O, it possesses an intrinsic negative Poisson's ratio of -0.021. Moreover, we found that the superconducting state of monolayer B2O can be improved, where strain plays an effective role in regulating the properties of the 2D material. The current results elucidate the structure and corresponding properties of monolayer B2O, which may stimulate related fundamental research and potential nanoscale applications.

Transition metal dichalcogenides have attracted significant attention due to both fundamental interest and their potential applications. Here, we have systematically explored the crystal structures of ReX2 (X = S, Se, and Te) over the pressure range of 0-300 GPa, employing swarm-intelligence-based structure prediction methodology. Several new structures are found to be stable at high pressures. The calculated enthalpy of formation suggested that all predicted high-pressure structures are stable against decomposition into elemental end-members. Moreover, we found that the simulated X-ray diffraction patterns of ReSe2 are in good agreement with experimental data. Pressure-induced metallization of ReX2 has been revealed from the analysis of its electronic structure. Our electron-phonon coupling calculations indicate ReSe2 and ReTe2 are superconducting phases at high pressures.

Carbon has the capability of forming various bonding states that affect the structures and properties of transition metal carbides. In this work, structural search was performed to explore the structural diversity of LaC2 at pressures of 0.0-30.0 GPa. Five stable structures of LaC2 reveal a variety of carbon structural units ranging from a dimer to bent C3, zigzag C4 and armchair polymer chains. A series of pressure-induced structural transformations are predicted, I4/mmm (i.e. experimental α phase) →C2/c→Pnma→Pmma, which involve the catenation of carbon from a dimer to zigzag C4 units and further to armchair polymer chains. The bent C3 unit appears in a novel Immm structure. This structure is the theoretical ground state of LaC2 under ambient conditions, but is kinetically inaccessible from the experimental α phase. LaC2 becomes thermodynamically metastable relative to La2C3 + diamond above 17.1 GPa, and eventually decomposes into constituent elements above 35.6 GPa. The presented results indicate that catenation of carbon can be realized even in simple inorganic compounds under nonambient conditions.