A semiconductor Sc2S3 monolayer with ultrahigh carrier mobility for UV blocking filter application.

For humans, ultraviolet (UV) light from sun is harmful to our eyes and eye-related cells. This detrimental fact requires scientists to search for a material that can efficiently absorb UV light while allowing lossless transmission of visible light. Using an unbiased first-principles swarm intelligence structure search, we explored two-dimensional (2D) Sc-S crystals and identified a novel Sc2S3 monolayer with good thermal and dynamical stability. The optoelectronic property simulations revealed that the Sc2S3 monolayer has a wide indirect bandgap (3.05 eV) and possesses an ultrahigh carrier mobility (2.8 × 103 cm2 V-1 s-1). Remarkably, it has almost transparent visible light absorption, while it exhibits an ultrahigh absorption coefficient up to × 105 cm-1 in the ultraviolet region. Via the application of biaxial strain and thickness modulation, the UV light absorption coefficients of Sc2S3 can be further improved. These findings manifest an attractive UV blocking optoelectronic characteristic of the Sc2S3 configuration as a prototypical nanomaterial for the potential application in UV blocking filters.

Exploring a novel two-dimensional metallic Y4C3 sheet applied as an anode material for sodium-ion batteries.

As novel "post lithium-ion batteries" and promising alternatives to lithium-ion batteries (LIBs) suffering from the limited Li resources, sodium-ion batteries (SIBs) are nowadays emerging and show bright prospects in large-scale energy storage applications due to abundant Na resources. However, a lack of suitable anode materials has become a key obstacle for the development of SIBs. Here we explore the potential of the two-dimensional (2D) Y-C space and identify a novel anode material for SIBs, a new Y4C3 sheet with P3̄m1 crystal symmetry, by means of first-principles swarm structure calculations. This Y4C3P3̄m1 structure has rather good kinetic and thermodynamic stability, possesses intrinsic metallicity, and remains metallic after adsorbing Na atoms, ensuring good electrical conductivity during the SIB cycle. Remarkably, a Y4C3 sheet as an anode for SIBs possesses the essential properties of a high specific capacity (∼752 mA h g-1), a low barrier energy (∼0.1 eV), and suitable open-circuit voltage (0-0.15 V). These characteristics are comparable and even superior to those of another known 2D Y2C anode material, indicating that the Y4C3 sheet can act as an appealing new candidate as an anode material for SIBs and offering new insights into the 2D Y-C space.

Exploring the structures and properties of nickel silicides at the pressures of the Earth's core.

Given the highly possible existence of nickel and silicon in the Earth's core, the study of the reaction between Ni and Si and the resulting structures at the pressure corresponding to that of the Earth's core is highly required. Therefore, we have investigated the crystal structures of Ni-Si compounds at pressures of 0-350 GPa by adopting a crystal structure search algorithm in conjunction with first-principles calculations. We uncover two high Ni-content Ni5Si and Ni6Si compounds with 12-coordination Si bonded with Ni, with both showing strong chemical stability in the Earth's core. Bonding analysis reveals that the Ni atoms in these Ni-Si compounds present oxidant features and act as electron acceptors. This distinctive anomaly is the natural result of the energy shifts of the Ni 3d and Si 3p bands, resulting in charge transfer from Si to Ni. By examining the key properties (e.g., density and sound velocities) of the Ni5Si and Ni6Si compounds, the obtained density lies within the range of the Earth's inner core, and the estimated sound velocities are found to be consistent with seismic data. These results indicate that these two compounds could be considered as possible core constituents. Our findings provide valuable insights into the enigmatic Earth's core as well as geophysical and geochemical processes.

Novel structural phases and the electrical properties of Si3B under high pressure.

We report a detailed theoretical study of the electronic structure, phase stability, elastic and mechanical properties of Si3B in the pressure range of 0-160 GPa by employing the crystal structure analysis by particle swarm optimization (CALYPSO) method combined with first-principles calculations. Our theoretical predictions reveal that, as the pressure increases, Si3B moves through the following sequence of phases: P3121 → C2/m → P21/m, and the corresponding transition pressures are computed to be 30 and 64 GPa, respectively. The results of band structures, density of states and electronic localization functions indicate that all three phases act as metallic with strong covalent bonding. The Vickers hardness of C2/m and P21/m phases has been estimated by Gao's, Lyakhov-Oganov's and Simunek's models, implying that Si3B is a potential hard material with a hardness value of ∼20 GPa. The superconducting critical temperatures of polymeric Si3B are also uncovered to be 3.6 K for the C2/m phase at 50 GPa and 5.7 K for the P21/m phase at 100 GPa. Our results enrich the crystal structures of the Si-B system and provide a further understanding of structures and their properties.

Density functional theory-based study on the structural, electronic and spectral properties of gas-phase PbMg n - (n = 2-12) clusters.

Gas-phase PbMg n- (n = 2-12) cluster structures were globally searched on their potential energy surfaces by means of the CALYPSO prediction software. Structural optimization and calculations of properties such as relative energy and electronic structure were then carried out by density functional theory for each size of low energy isomer. The structural, relative stability, natural charge population, natural electronic configuration and distribution of the strongest peaks of the infrared and Raman spectra of the low energy isomers of PbMg n- (n = 2-12) clusters were systematically investigated in the present work. It was shown that the PbMg7- cluster ground state isomer exhibits the highest stability, for which special electronic excitation and chemical bonding analyses were performed. It is reasonable to believe that this work enriches the structural, spectroscopic and other data of magnesium-based clusters and provides some theoretical basis for possible future experimental syntheses.

Discovery of Dome-Shaped Superconducting Phase and Anisotropic Transport in a van der Waals Layered Candidate NbIrTe4 under Pressure.

The unique electronic structure and crystal structure driven by external pressure in transition metal tellurides (TMTs) can host unconventional quantum states. Here, the discovery of pressure-induced phase transition at ≈2 GPa, and dome-shaped superconducting phase emerged in van der Waals layered NbIrTe4 is reported. The highest critical temperature (Tc ) is ≈5.8 K at pressure of ≈16 GPa, where the interlayered Te-Te covalent bonds form simultaneously derived from the synchrotron diffraction data, indicating the hosting structure of superconducting evolved from low-pressure two-dimensional (2D) phase to three-dimensional (3D) structure with pressure higher than 30 GPa. Strikingly, the authors have found an anisotropic transport in the vicinity of the superconducting state, suggesting the emergence of a "stripe"-like phase. The dome-shaped superconducting phase and anisotropic transport are possibly due to the spatial modulation of interlayer Josephson coupling .

Structural, mechanical and electronic properties and hardness of ionic vanadium dihydrides under pressure from first-principles computations.

Based on a combination of the CALYPSO method for crystal structure prediction and first-principles calculations, we explore the crystal structures of VH2 under the pressure range of 0-300 GPa. The cubic Fm-3m phase with regular VH8 cubes is predicted to transform into orthorhombic Pnma structure with fascinating distorted VH9 tetrakaidecahedrons at 47.36 GPa. Both the Fm-3m phase at 0 GPa and the Pnma phase at 100 GPa are mechanically and dynamically stable, as verified with the calculations of elastic constants and phonon dispersions, respectively. Moreover, the calculated electronic band structure and density of states indicate both stable phases are metallic. Remarkably, the analyses of the Poisson's ratio, electron localization function (ELF) and Bader charge substantiate that both stable phases are ionic crystals on account of effective charges transferring from V atom to H. On the basis of the microscopic hardness model, the Fm-3m and Pnma crystals of VH2 are potentially incompressible and hard materials with the hardness values of 17.83 and 17.68 GPa, respectively.

Exploration of high-pressure structural transition and electronic properties of BaFe2S3.

The iron-based compound BaFe2S3 has received considerable attention in recent years due to its unique electronic properties with important applications. But, there has been relatively little attention devoted to the structure evolution of BaFe2S3 under high pressure. Here, we report a detailed theoretical study of the structural, electronic and sound velocity properties of BaFe2S3 under high pressure by CALYPSO structure search method in combination with the first-principles calculations. We have uncovered three novel structures of BaFe2S3 under high pressure with space group P2221, Imm2, and C2/m symmetries. Theoretical calculations reveal that the structures of BaFe2S3 under high pressure satisfy the phase transition sequence of Cmcm → P2221 → Imm2 → C2/m, and the corresponding transition pressures are 31.6, 47.4 and 57.0 GPa, respectively. Our results enrich the high pressure phases of BaFe2S3 and will stimulate future experiments to synthesize these new phases.