Browsing by Author "Shi, W"

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    Relationships between Na+ distribution, concerted migration, and diffusion properties in rhombohedral NASICON
    (Wiley, 2020-06-24) Zou, ZY; Ma, N; Wang, AP; Ran, YB; Song, T; Jiao, Y; Zhou, H; Shi, W; He, B; Wang, D; Li, YJ; Avdeev, M; Shi, S
    Rhombohedral NaZr2(PO4)3 is the prototype of all the NASICON-type materials. The ionic diffusion in these rhombohedral NASICON materials is highly influenced by the ionic migration channels and the bottlenecks in the channels which have been extensively studied. However, no consensus is reached as to which one is the preferential ionic migration channel. Moreover, the relationships between the Na+ distribution over the multiple available sites, concerted migration, and diffusion properties remain elusive. Using ab initio molecular dynamics simulations, here it is shown that the Na+ ions tend to migrate through the Na1–Na3–Na2–Na3–Na1 channels rather than through the Na2–Na3–Na3–Na2 channels. There are two types of concerted migration mechanisms: two Na+ ions located at the adjacent Na1 and Na2 sites can migrate either in the same direction or at an angle. Both mechanisms exhibit relatively low migration barriers owing to the potential energy conversion during the Na+ ions migration process. Redistribution of Na+ ions from the most stable Na1 sites to Na2 on increasing Na+ total content further facilitates the concerted migration and promotes the Na+ ion mobility. The work establishes a connection between the Na+ concentration in rhombohedral NASICON materials and their diffusion properties. © 1999-2021 John Wiley & Sons, Inc.
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    Software for evaluating long-range electrostatic interactions based on the Ewald summation and its application to electrochemical energy storage materials
    (American Chemical Society, 2022-07-28) Shi, W; He, B; Pu, B; Ren, Y; Avdeev, M; Shi, SQ
    Electrochemical characteristics such as open-circuit voltage and ionic conductivity of electrochemical energy storage materials are easily affected, typically negatively, by mobile ion/vacancy ordering. Ordered phases can be identified based on the lattice gas model and electrostatic energy screening. However, the evaluation of long-range electrostatic energy is not straightforward because of the conditional convergence. The Ewald method decomposes the electrostatic energy into a real space part and a reciprocal space part, achieving a fast convergence in each. Due to its high computational efficiency, Ewald-based techniques are widely used in analyzing characteristics of electrochemical energy storage materials. In this work, we present software not only integrating Ewald techniques for two-dimensional and three-dimensional periodic systems but also combining the Ewald method with the lattice matching algorithm and bond valence. It is aimed to become a useful tool for screening stable structures and interfaces and identifying the ionic transport channels of cation conductors.