We develop a neuroevolution-potential (NEP) framework for generating neural network-based machinelearning potentials. They are trained using an evolutionary strategy for performing large-scale molecular dynamics (MD) simulations. A descriptor of the atomic environment is constructed based on Chebyshev and Legendre polynomials. The method is implemented in graphic processing units within the open-source GPUMD package, which can attain a computational speed over 10 7 atom-step per second using one Nvidia Tesla V100. Furthermore, per-atom heat current is available in NEP, which paves the way for efficient and accurate MD simulations of heat transport in materials with strong phonon anharmonicity or spatial disorder, which usually cannot be accurately treated either with traditional empirical potentials or with perturbative methods.

Different from the isotropic Dirac cones existing in other two-dimensional (2D) materials, anisotropic Dirac cones have the merit of anisotropic carrier mobility for applications in direction-dependent quantum devices. Motivated by the recent experimental finding of an anisotropic Dirac cone in borophene, here we report a new 2D anisotropic Dirac cone material, BS monolayer, identified by using a global structure search method and first-principles calculation combined with a tight-binding model. The BS monolayer is found to be stable mechanically, thermally, and dynamically and exhibits an anisotropic Dirac cone exactly at the Fermi level, showing a Fermi velocity of 10 m/s in the same order of magnitude as that of graphene. Moreover, BS monolayer is the first anisotropy Dirac cone material with a pristine honeycomb structure stabilized by S in free-standing conditions where each atom has four valence electrons on average being isoelectronic to C. This study would expand the Dirac cone material family with new features.

Based on ab initio evolutionary crystal structure search computation, we report a new phase of phosphorus called green phosphorus (λ-P), which exhibits the direct band gaps ranging from 0.7 to 2.4 eV and the strong anisotropy in optical and transport properties. Free energy calculations show that a single-layer form, termed green phosphorene, is energetically more stable than blue phosphorene and a phase transition from black to green phosphorene can occur at temperatures above 87 K. Due to its buckled structure, green phosphorene can be synthesized on corrugated metal surfaces rather than clean surfaces. The successful isolation of graphene [1], a single layer of carbon atoms in a two-dimensional (2D) honeycomb lattice, has generated tremendous interest in 2D layered materials [2]. Various applications using graphene have been explored based on the unusual properties such as massless Dirac fermions, high mobility, and high thermal conductivity [3, 4]. However, the gapless nature of graphene has been an obstacle in practical applications for electronic devices due to its low on/off ratios [5]. Transition metal dichalcogenides belonging to the family of 2D materials have the semiconducting gaps in the visible range, but the carrier mobility in thin films is significanlty reduced [6]. Recently, atomically thin black phosphorus has been successfully separated from its lay-ered bulk [7, 8], and this emerging 2D material with the tunable band gap by varying the number of atomic layers bridges the gap between graphene and transition metal dichalcogenides [9, 10]. Due to its high anisotropic mobility , black phosphorus is considered as a promising material for electronic and optoelectronic devices [6-8, 11, 12]. Elemental phosphorus is known to exist in several three-dimensional (3D) allotropes, such as red, white, and violet phosphorus, besides black phosphorus (α-P) which is the most stable phase among them. Due to the presence of various phases, it is expected that an unknown phosphorus allotrope will form under the control of substrate, temperature, and pressure. Zhu and Tománek proposed a new stable phase of phosphorus called blue phosphorus (β-P), with the structural similarity to a buckled graphene [13]. Unlike black phosphorus, blue phosphorus displays the indirect band gaps, regardless of the number of atomic layers. Other 2D structures such as γ-, δ-, ε-, ζ-, η-, θ-, and ψ-phosphorene were later suggested based on theoretical calculations [14-18]. Recently, blue phosphorene has been successfully synthesized on the Au(111) substrate by molecular beam epi-taxy [19]. The realization of blue phosphorene not only opens up the potential of various metastable allotropes but also motivates research into a new level of phosphorus that provides exciting characteristics such as broad band gaps and high anisotropic mobility. In this work, we use an ab initio evolutionary crystal structure search method to explore a new phosphorus allotrope called green phosphorus. The new P allotrope belongs to a class of 2D materials an...

Novel fully polymeric conductive hydrogel was developed based on liquid metal nanoparticles (LMNPs) initiated and cross-linked poly(acrylic acid) (PAA) backbone with poly(3,4-ethylenedioxythiophene):sulfonated bacterial cellulose nanofiber (PEDOT:BCNF) nanomaterials as the conductive...

Lipoic acid (LA), which originates from animals and plants, is a small biomass molecule and has recently shown great application value in soft conductors. However, the severe depolymerization of LA places a significant limitation on its utilization. A strategy of using Li‐bonds as both depolymerization quenchers and dynamic mediators to melt transform LA into high‐performance ionoelastomers (IEs) is proposed. They feature dry networks while simultaneously combining transparency, stretchability, conductivity, self‐healing ability, non‐corrosive property, re‐mouldability, strain‐sensitivity, recyclability, and degradability. Most of the existing soft conductors’ drawbacks, such as the tedious synthesis, non‐renewable polymer networks, limited functions, and single‐use only, are successfully solved. In addition, the multi‐functions allow IEs to be used as soft sensors in human–computer interactive games and wireless remote sports assistants. Notably, the recycled IE also provides an efficient conductive filler for transparent ionic papers, which can be used to design soft transparent triboelectric nanogenerators for energy harvesting and multidirectional motion sensing. This work creates a new direction for future research involving intelligent soft electronics.

Transition metal dinitrides (TMDNs) have attracted increasing attention for their rich chemistry, intriguing properties, and potential applications in electronic devices and electrodes. The similarity in atomic ratio with transition-metal dichalcogenide (TMD) sheets leads to an assumption in previous studies that TMDN sheets adopt similar geometry to that of TMD sheets. Here, using global particle-swarm optimization method combined with first-principles calculations, we show a distinct structure of YN2 monolayer containing isolated N2 dimers labeled as O-YN2, which is dynamically, thermally and mechanically stable, and energetically favorable over the previously predicted H- and T-YN2 monolayer structures. Moreover, because of its unique atomic configuration, the O-YN2 sheet is metallic, providing an intrinsic advantage in electrical conductivity over those semiconducting or insulating transition-metal oxides and TMD layers. In particular, we find that O-YN2 is a promising anode material for potassium ion batteries (KIBs) with competitive potassium capacity, low open-circuit voltage, and small migration barrier compared with other anode materials for potassium ion batteries, adding new features to 2D materials family.

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Ionic conductive hydrogels have attracted much attention in artificial electronic skin and wearable strain sensors. However, most of hydrogel-based sensors exhibit poor mechanical properties and limited sensitivity. Herein, a highly...