npj: 铁—高斯近似势预测螺旋位错的结构和迁移率
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bcc过渡金属上升到中等温度时的塑性流动行为，主要由螺位错的热激活滑移控制，而螺位错的热激活滑动反过来又由原子级螺位错核心结构和相关的滑动扭结对成核机制决定。模拟复杂的塑性现象需要模拟许多原子以及相互作用的位错和缺陷，相关模拟尺度已超乎第一性原理方法的范围，因此需要经验的原子间相互作用势才能模拟。很奇怪，对于作为bcc Fe的技术重要案例来说，现有的经验原子间相互作用势会导致虚假结果。
来自瑞士洛桑联邦理工学院Francesco Maresca领导的研究小组，使用新近为铁研究而开发的高斯近似势（GAP），通过分子静力学和分子动力学模拟，得出了螺位错行为的各个方面，并对其结果用密度泛函理论（DFT）计算作了验证。具体来说，他们用GAP预测出Fe的一个紧凑的非退化的核心结构、一个单峰Peierls势，以及在{110}上的滑移，并发现其与DFT计算结果一致。在有限温度下，通过预期的扭结对成核和扩张机制发生了热激活化运动。使用缠结弹性带方法计算的螺旋运动的应力依赖性焓垒，紧密地遵循标准理论预测的形式，其所具有的~1eV零应力势垒，接近实验值的0.84eV，而且所预测的~2 GPa Peierls应力也与DFT预测的Peierls势一致。这种势还可用于验证许多其他重要塑性现象的原子尺度的起源，例如与辐射损伤相互作用的位错，以及铁和其他体心立方材料中的裂缝。
该文近期发表于npj Computational Materials 4: 69 (2018)，英文标题与摘要如下，点击左下角“阅读原文”可以自由获取论文PDF。
Screw dislocation structure and mobility in body centered cubic Fe predicted by a Gaussian Approximation Potential
Francesco Maresca, Daniele Dragoni, Gábor Csányi, Nicola Marzari & William A. Curtin
The plastic flow behavior of bcc transition metals up tomoderate temperatures is dominated by the thermally activated glide of screwdislocations, which in turn is determined by the atomic-scale screw dislocationcore structure and the associated kink-pair nucleation mechanism for glide. Modelingcomplex plasticity phenomena requires the simulation of many atoms andinteracting dislocations and defects. These sizes are beyond the scope offirst-principles methods and thus require empirical interatomic potentials. Especiallyfor the technological important case of bcc Fe, existing empirical interatomic potentialsyield spurious behavior. Here, the structure and motion of the screwdislocations in Fe are studied using a new Gaussian Approximation Potential(GAP) for bcc Fe, which has been shown to reproduce the potential energysurface predicted by density-functional theory (DFT) and many associatedproperties. The Fe GAP predicts a compact, non-degenerate core structure, asingle-hump Peierls potential, and glide on {110}, consistent with DFT results.The thermally activated motion at finite temperatures occurs by the expectedkink-pair nucleation and propagation mechanism. The stress-dependent enthalpybarrier for screw motion, computed using the nudged-elastic-band method,follows closely a form predicted by standard theories with a zero-stressbarrier of ~1eV, close to the experimental value of 0.84eV, and a Peierls stress of ~2GPaconsistent with DFT predictions of the Peierls potential.
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