我们的系列文章致力于使用高性能图形处理器（GPU）在刚性离子和对相互作用（RIPI）近似下对混合锕系元素-氧化物（MOX）燃料进行高精度分子动力学模拟。本文利用最近广泛使用的十组原子间对势（SPP），在周期（PBC）和孤立（IBC）边界条件下，研究了二氧化铀（UO 2）中氧负离子的自扩散机制。测量的扩散系数范围很广（从熔点时的10^-3 cm ^2/s到1400 K时的10^-12 cm ^2/s），这使得模拟结果与实验数据（仅在低温（T < 1500 K）下已知）的直接比较（无需外推）成为可能。一个非常详细的（1 K的温度步长）计算的扩散系数使我们能够绘制的扩散激活能及其衍生物的温度依赖性，这两者都显示了一个宽（~1000 K）的超离子过渡区确认了我们之前获得的热容量的宽的峰值。结果表明，在无表面缺陷或人工嵌入缺陷的模型晶体中，阴离子自扩散不受SPP影响，而是通过交换机制进行，而不是以往工作中所认为的间隙或空位机制。交换扩散激活能与晶格静力学计算的反Frenkel缺陷形成能相吻合。
英文摘要：
Our series of articles is devoted to high-precision molecular dynamics simulation of mixed actinide-oxide (MOX) fuel in the approximation of rigid ions and pair interactions (RIPI) using high-performance graphics processors (GPU). In this article we study self-diffusion mechanisms of oxygen anions in uranium dioxide (UO2) with the ten recent and widely used sets of interatomic pair potentials (SPP) under periodic (PBC) and isolated (IBC) boundary conditions. Wide range of measured diffusion coefficients (from 10^-3 cm^2/s at melting point down to 10^-12 cm^2/s at 1400 K) made possible a direct comparison (without extrapolation) of the simulation results with the experimental data, which have been known only at low temperatures (T < 1500 K). A highly detailed (with the temperature step of 1 K) calculation of the diffusion coefficient allowed us to plot temperature dependences of the diffusion activation energy and its derivative, both of which show a wide (~1000 K) superionic transition region confirming the broad lambda-peaks of heat capacity obtained by us earlier. It is shown that regardless of SPP the anion self-diffusion in model crystals without surface or artificially embedded defects goes on via exchange mechanism, rather than interstitial or vacancy mechanisms suggested by the previous works. The activation energy of exchange diffusion turned out to coincide with the anti-Frenkel defect formation energy calculated by the lattice statics.
Revealing Hydroxide Ion Transport Mechanisms in Commercial Anion-Exchange Membranes at Nano-Scale from Machine-learned Interatomic Potential Simulations
Technische Universität Ilmenau（伊尔梅瑙工业大学）；Fraunhofer-Institut für Keramische Technologien und Systeme IKTS（弗劳恩霍夫陶瓷技术与系统研究所）
Origin of the glass-like dynamics in molecular metals $\pmbκ$-(BEDT-TTF)$_{\textbf{2}}$X: implications from fluctuation spectroscopy and $\pmb{\textit{ab initio}}$ calculations
