Accelerated atomistic simulation of dislocations in nuclear materials

该研究计划旨在改进和使用计算机模拟来研究加拿大核电反应堆中使用的金属和合金的关键机械性能。这些模拟将集中在几个原子到几百万个原子的材料的物理特性上。更具体地说，位错的动力学将被建模，具有前所未有的现实主义水平，既通过精确地建模原子间的相互作用，并通过达到与实验时间尺度相当的时间尺度。 位错及其与辐射诱导缺陷的相互作用在确定核电应用中的结构材料的性能方面起着关键作用。当材料暴露于中子辐射时，它们会导致有害影响，如辐射诱导硬化和脆化。 这些效应产生于发生在原子（纳米）水平和尺度上的宏观尺度的过程。对它们进行建模的典型模拟工作有两个主要问题。首先，物理模型来表达原子间的相互作用有有限的预测能力的背景下，位错动力学，特别是在合金。其次，传统模拟方法的时间尺度（几十纳秒）太短，无法模拟真实应变率下的位错运动（典型的模拟比实验快10个数量级）。 本研究项目的目的就是解决这两个问题。原子间的相互作用问题将通过开发一种进化算法来解决，其中不仅有可调参数，而且函数形式本身也被优化。与时间尺度有关的问题将通过扩展动力学激活弛豫技术（一种加速动力学形式）来处理位错来解决。 从技术角度来看，这是一个雄心勃勃的研究计划。它需要最先进的方法，如进化算法，机器学习和加速动力学。这将需要参与该项目的研究生掌握和改进这些方法，这本身应该是原子模拟社区的极大兴趣。此外，在原子水平上精确模拟位错动力学的能力不仅将对加拿大核电应用产生深远的影响，而且还将对其他金属和合金的研究产生深远的影响，特别是在建筑或运输方面。

This research program aims to improve and use computer simulations to investigate crucial mechanical properties of metals and alloys used in Canadian nuclear power reactors. These simulations will focus on physical properties of the materials on the scale of a few atoms to a few million atoms. More specifically, the kinetics of dislocations will be modeled, with an unprecedented level of realism, both by modeling inter-atomic interactions accurately and by reaching timescales that are comparable with experimental timescales. Dislocations and their interactions with radiation-induced defects play a critical role in determining the properties of structural materials in nuclear power applications. They lead to deleterious effects such as radiation-induced hardening and embrittlement, as the materials are exposed to neutron radiation. These effects arise from processes that take place at the atomic (nano-) level and scale up to the macro-scale. Typical simulations efforts to model them have two major issues. First, the physical models to express interatomic interactions have limited predictive ability in the context of dislocation kinetics, especially in alloys. Second, the timescales accessible to conventional simulation methodsa few tens of nanosecondsare too short to simulate dislocation motion at realistic strain rates (typical simulations are 10 orders of magnitude faster than experiments). The objective of this research project is to address these two issues. The interatomic interactions issue will be addressed by developing an evolutionary algorithm, where not only are there adjustable parameters, but where the functional form is itself optimized. The issue related to timescales will be addressed by extending the kinetic Activation Relaxation Technique, a form of accelerated dynamics, to handle dislocations. This is a ambitious research plan, from a technical point of view. It requires state-of-the-art methods, such as evolutionary algorithms, machine learning and accelerated dynamics. This will require the graduate students involved in the project to master and improve these methods, which should in itself be of great interest for the atomistic simulations community. Furthermore, the ability to accurately model dislocation dynamics at the atomic level will have a profound impact not only for Canadian nuclear power applications, but also for the study of other metals and alloys, notably in the context of construction or transportation.