Nanowires exfoliated from one-dimensional van der Waals transition metal trihalides and quadrihalides.

The exfoliation of van der Waals (vdW) materials has been widely used to fabricate two-dimensional (2D) materials. However, the exfoliation of vdW materials to isolate atomically thin nanowires (NWs) is an emerging research topic. In this letter, we identify a large class of transition metal trihalides (TMX3), which have one-dimensional (1D) vdW structures, i.e., they comprise columns of face-sharing TMX6 octahedral chains, whereas the chains are bound by weak vdW forces. Our calculations show that the single-chain and multiple-chain NWs constructed from these 1D vdW structures are stable. The calculated binding energies of the NWs are relatively small, suggesting that it is possible to exfoliate NWs from the 1D vdW materials. We further identify several 1D vdW transition metal quadrihalides (TMX4) that are candidates for exfoliation. This work opens a paradigm for exfoliating NWs from 1D vdW materials.

Two-Dimensional Planar BGe Monolayer as an Anode Material for Sodium-Ion Batteries.

Using first-principles swarm intelligence structure prediction computations, we explore a fully planar BGe monolayer with unique mechanical and electrical properties. Theoretical calculations reveal that a free-standing BGe monolayer has excellent stability, which is confirmed by the cohesive energy (compared to experimentally synthetic borophene and germanene monolayers), phonon modes (no imaginary frequencies appeared in the phonon spectrum), ab initio molecular dynamics (AIMD) simulations (no broken bonds and geometric reconstructions), and mechanical stability criteria. The metallic feature of the BGe monolayer can be maintained after absorbing different numbers of Na atoms, ensuring good electronic conductivity during the charge/discharge process. The calculated migration energy barrier, open-circuit voltage, and theoretical specific capacity of the BGe monolayer are much better than those of some other two-dimensional (2D) materials. These findings render the BGe monolayer a potential candidate for reversible Na-ion battery anode materials with desirable performance.

Construction of crystal structure prototype database: methods and applications.

Crystal structure prototype data have become a useful source of information for materials discovery in the fields of crystallography, chemistry, physics, and materials science. This work reports the development of a robust and efficient method for assessing the similarity of structures on the basis of their interatomic distances. Using this method, we proposed a simple and unambiguous definition of crystal structure prototype based on hierarchical clustering theory, and constructed the crystal structure prototype database (CSPD) by filtering the known crystallographic structures in a database. With similar method, a program structure prototype analysis package (SPAP) was developed to remove similar structures in CALYPSO prediction results and extract predicted low energy structures for a separate theoretical structure database. A series of statistics describing the distribution of crystal structure prototypes in the CSPD was compiled to provide an important insight for structure prediction and high-throughput calculations. Illustrative examples of the application of the proposed database are given, including the generation of initial structures for structure prediction and determination of the prototype structure in databases. These examples demonstrate the CSPD to be a generally applicable and useful tool for materials discovery.

Catenation of carbon in LaC2 predicted under high pressure.

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.