The low-alloyed steels are widely-used structural materials in radiation environments and among their various alloying elements the non-metallic element Si is usually essential. However, due to the different bonding features, it is difficult to describe the atomistic behaviors of Fe-Si with interatomic potentials. The current study presents an angular-dependent interatomic potential of Fe-Si, which can well describe the physical properties including lattice constants and mixing enthalpy of Fe-Si solid solutions. Specifically, the potential satisfactorily describes the formation energies of radiation defects in Fe-Si alloy. Applying this potential, molecular dynamics simulations are employed to investigate the radiation damage in Fe-Si solid solutions. It turns out that the addition of Si does not significantly affect the Frenkel pairs produced by collision cascades. However, Si appears to increase the fraction of mono-vacancy in Fe-Si steels. (C) 2020 Published by Elsevier B.V.

The search for high-performance p-type transparent conductors is crucial to many emerging optoelectronic applications. Motivated by the pioneer predictions of the existence of intrinsic p-type conductivity in several wide-gap layered halide double perovskites, Hu et al. synthesize the Cs4CdSb2Cl12 compound, but fail to observe the p-type conductivity. They argue that the different conclusion is mostly due to the chemical potential boundary overestimation and bandgap underestimation in the initial calculations. In this study, based on the additional calculations, it is demonstrated that these two factors raised by Hu et al. will not affect the major conclusions, although the pinned Fermi level (EF-pin) can slightly be changed. Importantly, it is found that the different conclusion obtains by Xu et al. and Hu et al. is mostly due to the different crystal phases adopted, which can have a big impact on the calculated EF-pin positions and the resulting p-type performance. Finally, besides the careful control of growth conditions for reaching the ideal p-type chemical potential regions, it is suggested that a moderate strain/pressure or fast quenching may be further adopted to enhance the p-type conductivity in Cs4CdSb2Cl12 and other similar compounds for better experimental observations. © 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

An analytic incremental model is proposed to predict the defect production upon cascade overlapping. By resolving the coupled annealing events during cascade overlapping, this model handles cascade overlapping with multiple pre-existing defects of different sizes and number densities. The model is first parameterized and then applied to bcc-Fe. The proposed model satisfyingly reproduces the defect production obtained by molecular dynamics simulations with various radiation damage levels and defect cluster size distributions. The present model provides an essential description of the primary source of radiation damage, especially for high dose irradiation, and could be used in conjunction with reactive diffusion models for better understanding of radiation damage.

Half-metallic ferromagnets (HMFs) that possess intriguing physical properties with completely spin-polarized current are key candidates for high-efficiency spintronic devices. However, HMFs that could simultaneously have high Curie temperature (Tc), wide half-metallic gap (ΔHM), and large bulk magnetocrystalline anisotropy energy (MAE) are very rare, which significantly restrict their room-temperature (RT) applications. In this article, through materials screening in layered halide double perovskites (LHDPs), we have theoretically identified that Cs4FePb2Cl12, which has good crystallographic, dynamic and thermal stabilities, possesses an intrinsic half-metallic ground-state with a high Tc ~ 450 K. Interestingly, the long-range ferromagnetic ordering in bulk Cs4FePb2Cl12 is contributed by the strong super-superexchange interactions between the neighboring Fe d orbitals mediated by different anionic Cl p orbitals. The high Tc of layered Cs4FePb2Cl12 can be well maintained even in the monolayer limitation, i.e., Tc ~ 370 K for Cs4FePb2Cl12 monolayer, which is critical for nanoscale device applications. Moreover, both bulk and monolayer Cs4FePb2Cl12 can exhibit wide ΔHM ~ 0.55 eV and large MAE >320 μeV/Fe, comparable to that of the best HMFs reported in the literature. Our findings can significantly extend the potentials of LHDPs for high-temperature spintronic applications. © 2019, The Author(s).

A realistic interatomic potential of Mg-Ca-Ag system is constructed under a proposed modified tight-binding scheme with the aid of ab initio calculations. Then, the favored and optimized compositions for forming Mg-Ca-Ag metallic glasses are investigated by means of the potential-based molecular dynamics simulations of atomistic modeling. The calculation shows that the Mg-Ca-Ag ternary system is liable to form amorphous alloys and the favored compositions for metallic glass formation locate at a sub-region, where the amorphization driving force is greater than that of other regions. Notably, we improve the conventional method of removing the facets in the amorphous structure analysis, and we introduce K-means clustering to eliminate the facets of the Voronoi polyhedra, which allows more reasonable description of various geometries of the different central atoms and their neighboring atoms. Then, both the Voronoi tessellation method and the Honeycutt-Andersen pair analysis are used to describe the disordered structure in Mg50Ca30Ag20 metallic glass based on the result of K-means clustering. Our work provides good guidance for composing the Mg-Ca-Ag metallic glasses, and further verifies the microstructure of the amorphous alloys. © 2019 Author(s).

Ab initio calculations were conducted to assist the construction of the n-body potential of the Ti-Nb-Al ternary metal system. Applying the constructed Ti-Nb-Al interatomic potential, molecular dynamics and Monte Carlo simulations were performed to predict a quadrilateral composition region, within which metallic glass was energetically favored to be formed. In addition, the amorphous driving force of those predicted possible glassy alloys was derived and an optimized composition around Ti15Nb45Al40 was pinpointed, implying that this alloy was easier to be obtained. The atomic structure of Ti-Nb-Al metallic glasses was identified by short-, medium-, and extended-range analysis/calculations, and their hierarchical structures were responsible to the formation ability and unique properties in many aspects.

按照《申请书》和《计划书》要求开展工作，采用归纳分析和计算模拟方法研究了若干复杂结构金属体系的多体势及非晶合金形成原子集团特征等科学问题。取得主要成果:1)提出了可以反映角度因素的多体势函数形式，并成功地应用到铀金属及其合金等；提2)提出了了固相形核生长的内生长和外生长的概念。快速淬火时，固相的外生长远远大于内生长速度而导致非晶形成;3)理论计算表明，纳米尺度的晶相比非晶相颗粒具有更强的尺寸效应，当尺度低于某一临界值时，纳米非晶相比晶相更容易形成。4)结构分析表明金属玻璃的原子构型存在着多层次结构：由中心原子及近邻原子构成的原子团簇，由各种原子团簇复杂交联形成的团簇群，团簇群展布穿插形成结构骨架、进而形成复杂的空间分形网络(长程分形序)。5)和其它课题联合共同培养毕业4名博士和1名硕士研究生，发表20篇SCI论文，参加会议交流8人次。

U-Ti alloy is a kind of metallic nuclear fuel that has been of interest to the nuclear power industry. Nuclear fuel is exposed to an aggressive physical, chemical and radiative environment, and may suffer corrosion damage caused by irradiation or chemicals like water vapour. Surface adsorption is the very start of the corrosion process. In this work, basing on the density functional theory (DFT) corrected for on-site Coulomb interactions (DFT + U), we investigate the adsorption behavior of H2O on U2Ti surface. U2Ti (1 1 0) surface is predicted to be the most stable one using DFT + U calculations. Eight possible sites are chosen to conveniently demonstrate the chemical circumstance on the (1 1 0) surface. Our study shows that the adsorption of H2O on U2Ti (1 1 0) surface is a mixed adsorption involving both physisorption and chemisorption. Physisorption can be observed on all these sites with an equilibrium distance, while chemisorption can only occur on some sites, mostly represented as dissociative adsorption. Density of states and deformation charge density are also calculated to examine the charge transfer between surface atoms as well as atoms in the bulk. A climbing image nudged elastic band (CI-NEB) method is used to determine the energy barriers for H2O migrating from the equilibrium position of physisorption to the states of dissociative adsorption. Bader charge analysis was performed to determine the numerical values of charge on each adsorbed atom. © 2019 Elsevier B.V.

All-inorganic perovskites with improved stability are expected to be better candidates for optoelectronics, compared to organic-inorganic hybrid perovskites. A new member of all-inorganic perovskites, CsPb2Br5, has attracted great attention for its promising applications in optoelectronic devices. However, the origins of the green emission in CsPb2Br5 have been actively debated. By using first-principles calculations, we find that CsPb and VBr are dominant intrinsic defects independent of the growth conditions within the stable region of CsPb2Br5. Interestingly, we suggest that individual intrinsic defects do not lead to the green emission of CsPb2Br5, while the donor-acceptor pair recombination of CsPb and VBr possibly does. Our findings provide new insights into the experimental controversy about the green emission and its origins in CsPb2Br5 from the perspective of intrinsic defects, which help to extend the application of CsPb2Br5 in optoelectronic devices. Copyright © 2019 American Chemical Society.