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.

The present study of structure-property relationships and disclosure of fascinating amplified spontaneous emission (ASE) behavior of an organic molecule not only exhibits the individual effect of molecular conformation and arrangement on the emission properties of the crystal separately, but also indicates that some concealed elegant properties of organic solids can be achieved through manipulating the polymorphic form.

Graphene and phosphorene are two major types of atomically thin two-dimensional materials under extensive investigation. However, the zero band gap of graphene and the instability of phosphorene greatly restrict their applications. Here, we make first-principle unbiased structure search calculations to identify a new buckled graphene-like PC6 monolayer with a number of desirable functional properties. The PC6 monolayer is a direct-gap semiconductor with a band gap of 0.84 eV, and it has an extremely high intrinsic conductivity with anisotropic character (i.e., its electron mobility is 2.94 × 105 cm2 V–1 s–1 along the armchair direction, whereas the hole mobility reaches 1.64 × 105 cm2 V–1 s–1 along the zigzag direction), which is comparable to that of graphene. On the other hand, PC6 shows a high absorption coefficient (105 cm–1) in a broad band, from 300 to 2000 nm. Additionally, its direct band gap character can remain within a biaxial strain of 5%. All these appealing properties make the predicted PC6 monolayer a promising candidate for applications in electronic and photovoltaic devices.

Observation of high-temperature superconductivity in sulfur hydrides at megabar pressures has generated an irresistible wave on searching for new superconductors in other compressed hydrogen-rich compounds. An immediate effort is towards exploration of the relevant candidate of tellurium hydrides, where tellurium is isoelectronic to sulfur but it has a heavier atomic mass and much weaker electronegativity. The hitherto unknown phase diagram of tellurium hydrides at high pressures was investigated by a first-principles swarm structure search. A recent breakthrough finding in the superconductivity field is the observation of remarkably high superconductivity (with T c up to 190 K) in sulfur dihydride (H 2 S) under pressure [1]. This observation was achieved by a direct investigation on a theoretical prediction of high-T c superconductivity in compressed solid H 2 S within the framework of Bardeen-Cooper-Schrieffer (BCS) theory [2,3]. The superconductive mechanism of H 2 S and its possible decomposition at high pressures was then substantially explored [4][5][6][7][8][9]. Besides these efforts, findings of new superconductors in other relevant hydrogen-containing compounds have also attracted great attention. Selenium (Se) hydrides were already predicted to exhibit high T c in the range of 40-131 K at megabar pressures [10,11].Tellurium (Te) is the next group-VI element isoelectronic to S and Se. However, Te adopts an even larger atomic core with a much weaker electronegativity, and therefore it exhibits a rather different chemistry from S and Se. As a result, stable H 2 S [12] and H 2 Se [13] gas molecules and their solid counterparts exist at ambient pressure, whereas H 2 Te gas molecules are unstable and rapidly decompose into the constituent elements (above −2 °C) [14]. Thus far, there is lack of any report on stable Te hydrides.Pressure can fundamentally modify chemical reactivity of elements, and overcome the reaction barrier of hydrogen and certain substances to form stable hydrides (e.g. noble metal hydrides [15,16] There is a possibility that Te hydrides can be synthesized by compressing a mixture of Te + H 2 . As to the superconductivity, on one hand one may argue that Te hydrides might not be good candidates for high-T c superconductors since the low Debye temperature caused by heavy Te can suppress the superconductivity. On the other hand, low-frequency vibrations (soft phonons) associated with a larger atomic mass can enhance electron-phonon coupling (EPC) [20] as seen from the predicted higher T c (up to 80 K) in SnH 4 [21] than those in SiH 4 (up to 17 K) [22] and GeH 4 (up to 64 K) [23].We herein extensively explored the high-pressure phase diagram of Te hydrides by using the swarm-intelligence based CALYPSO structural prediction calculations [24,25]. Distinct from S and Se hydrides, Te hydrides exhibit a unique potential energy landscape, where the unexpected stoichiometries of H 4 Te, H 5 T 2 and HTe 3 emerge as stable species at megabar pressures. H 4 Te is so far the most H-rich stoichiometry re...