Sodium-ion batteries (SIBs) have attracted considerable attention due to the intrinsic safety and high abundance of sodium. However, the lack of high-performance anode materials becomes a main obstacle for the development of SIBs. Here, we identify an ideal anode material, a metallic TiC monolayer with not only remarkably high storage capacity of 1278 mA h g but also low barrier energy and open-circuit voltage, through first-principles swarm-intelligence structure calculations. TiC still keeps metallic after adsorbing two-layer Na atoms, ensuring good electrical conductivity during the battery cycle. Besides, high melting point and superior dynamical stability are in favor of practical application. Its excellent performance can be mainly attributed to the presence of an unusual n-biphenyl unit in the TiC monolayer. High cohesive energy, originating from multibonding coexistence (e.g., covalent, ionic, and metal bonds) in the TiC monolayer, provides strong feasibility for experimental synthesis. In comparison with TiC, functionalized TiC with oxygen shows a higher storage capacity; meanwhile, it keeps nearly the same barrier energy. This is in sharp contrast with metal-rich MXenes. These intriguing properties make the TiC monolayer a promising anode material for SIBs.

An important goal in chemistry is to prepare compounds with unusual oxidation states showing exciting properties. For gold (Au), the relativistic expansion of its 5d orbitals makes it form high oxidation state compounds. Thus far, the highest oxidation state of Au known is +5. Here, we propose high pressure as a controllable method for preparing +4 and +6 oxidation states in Au via its reaction with fluorine. First-principles swarm-intelligence structure search identifies two hitherto unknown stoichiometric compounds, AuF and AuF, exhibiting typical molecular crystal character. The high-pressure phase diagram of Au fluorides is rather different from Cu or Ag fluorides, which is indicated by stable chemical compositions and the pressures needed for the synthesis of these compounds. This difference can be associated with the stronger relativistic effects in Au relative to Cu or Ag. Our work represents a significant step forward in a more complete understanding of the oxidation states of Au.

Electrides are unique compounds where most of the electrons reside at interstitial regions of the crystal behaving as anions, which strongly determines its physical properties. Interestingly, the magnitude and distribution of interstitial electrons can be effectively modified either by modulating its chemical composition or external conditions (e.g., pressure). Most of the electrides under high pressure are nonmetallic, and superconducting electrides are very rare. Here we report that a pressure-induced stable Li 6 P electride, identified by first-principles swarm structure calculations, becomes a superconductor with a predicted superconducting transition temperature T c of 39.3 K, which is the highest among the already known electrides. The interstitial electrons in Li 6 P, with dumbbell-like connected electride states, play a dominant role in the superconducting transition. Other Li-rich phosphides, Li 5 P, Li 11 P 2 , Li 15 P 2 , and Li 8 P, are also predicted to be superconducting electrides, but with a lower T c. Superconductivity in all these compounds can be attributed to a combination of a weak electronegativity of phosphorus (P) with a strong electropositivity of lithium (Li), and opens up the interest to explore high-temperature superconductivity in similar binary compounds.

Sodium-ion batteries (SIBs) have become one of the most promising energy storage devices due to the high abundance and safety of sodium.

For the development of high-performance spintronic nanodevices, one of the most urgent and challenging tasks is the preparation of two-dimensional materials with roomtemperature ferromagnetism and a large magnetic anisotropic energy (MAE). Through firstprinciples swarm-intelligence structural search calculations, we identify an ideal ferromagnetic Fe 3 P monolayer, in which Fe atoms show a perfect Kagome lattice, leading to strong in-plane Fe−Fe coupling. The predicted Curie temperature of Fe 3 P reaches ∼420 K, and its MAE is comparable to those of ferromagnetic materials, such as Fe and Fe 2 Si. Moreover, the Fe 3 P monolayer remains as an above room-temperature ferromagnet under biaxial strains as large as 10%. Its lattice can be retained at temperatures of ≤1000 K, exhibiting a high thermodynamic stability. All of these desirable properties make the Fe 3 P monolayer a promising candidate for applications in spintronic nanodevices.

High pressure induces unexpected chemical and physical properties in materials. For example, hydrogen-rich compounds under pressure have recently gained much attention as potential room-temperature superconductors, and iron hydrides have also gained significant interest as potential candidates for being the main constituents of the Earth’s core. It is well-known that pressure induces insulator-to-metal transitions, whereas pressure-induced metal-to-insulator transitions are rare, especially for transition metal hydrides. In this article, we have extensively explored the structural phase diagram of iron hydrides by using ab initio particle swarm optimization. We have found a new stable stoichiometry, FeH6, above 213.7 GPa with C2/c symmetry. Interestingly, C2/c FeH6 presents an unexpected nonmetallicity, and its band gap becomes larger with increasing pressure. This is in sharp contrast with P21/m FeH4. The nonmetallicity of C2/c FeH6 mainly originates from the pressure-induced hybridization between the Fe and H orbitals. This new compound shows a unique structure with a mixture of nonbonded hydrogen atoms in a helical iron framework. The strong Fe–Fe interaction and ionic Fe–H bonds are responsible for its structural stability. In addition, we have also found a more stable tetragonal FeH2 structure with the same I4/mmm symmetry as the previously proposed one, the X-ray diffraction pattern of which perfectly agrees with that of the experiment.

Two dimensional TaC2is a promising anode material from the standpoint of a high specific capacity, fast Li diffusion rate, low operating voltage, and good electronic conductivity.

Our results represent a significant step towards understanding the structures and stabilities of lithium sulfide clusters, and improving the performance of Li–S batteries.