A Symmetry-Based Approach to Minimum Energy Pathways

非技术性描述：对称性在所有物理科学中都是一个强大的工具。扭曲，通常是原子轨迹的集合，对于理解一系列动力学材料过程非常重要，其中原子在外部刺激（如场，温度和应力）下移动。预测材料在经历变形时会采取哪条路径对于涉及这种原子运动的任何应用都很重要。然而，预测这样的路径，称为最小能量路径（MEP），目前在本质上是随机的，人们永远无法确定最终的结果。该项目旨在通过引入畸变-反转对称和畸变群等新思想，开发一种新的基于几何的框架和计算工具;它显著提高了搜索此类路径的速度、数值精度和综合性。理论预测的实验验证是本研究的另一个方面。对计算材料研究教育培训日益增长的需求正在通过密度泛函理论的实践研讨会，包括妇女和代表性不足的群体在内的研究本科生的积极指导，以及通过积极参与STEM学院的向上约束数学和科学计划，以及宾夕法尼亚州立大学千年学者计划，吸引和指导有才华的STEM学生参加本科课程。技术说明：这是一个综合的理论实验的建议，开发新的对称性的想法和计算工具，探索最小能量路径（MEP）的扭曲，更具体地说，铁电畴开关和畴壁运动。MEP是由轻推弹性带方法（NEB）计算的;然而，它目前依赖于随机过程和用户直觉的组合来构建初始路径。主要研究人员专注于路径对称群的概念，并开发了一个代码（准备好后将公开提供），以在量子咖啡（Quantum Espresso）中实现这些想法，这是一个开源的密度泛函理论（DFT）软件。三个模型系统类，即，在简单的钙钛矿，层状氧化物，并在多铁性，作出预测。使用实验技术，推动原位动态与2-5皮米计量学在电子显微镜，和超快电子衍射显微镜technology.This奖项反映了NSF的法定使命，并已被认为是值得通过使用该基金会的智力价值和更广泛的影响审查标准进行评估的支持。

Non-technical description: Symmetry is a powerful tool in all of physical sciences. Distortions, often a collection of atomic trajectories, are important for understanding a range of kinetic materials processes where atoms move under external stimuli such as fields, temperature, and stress. Predicting which path a material would take in undergoing a distortion is important for any application which involves such atomic motion. However, predicting such paths, called minimum energy pathways (MEPs), is currently stochastic in nature, and one can never be sure of the final results. This project aims at developing a new symmetry-based framework and computational tools through the introduction of new ideas such as distortion-reversal symmetry and distortion groups; it significantly improves the speed, numerical accuracy, and the comprehensive nature of search for such paths. Experimental verification of the theory predictions is the other aspect of this research. The growing need for educational training in computation materials research is being addressed with hands-on workshops in density-functional theory, active mentoring of undergraduates in research including women and underrepresented groups, and through active participation in STEM Academy of the Upward Bound Math and Science Program, as well as Penn State Millennium Scholars Program that attracts and guides talented STEM students to the undergraduate program. Technical description: This is an integrated theory-experimental proposal that develops new symmetry ideas and computational tools to explore minimum energy pathways (MEPs) for distortions, and more specifically, for ferroelectric domain switching and domain wall motion. The MEPs are computed by the Nudged Elastic Band method (NEB); however, it currently relies on a combination of stochastic process and user intuition to construct initial paths. The principal investigators are focused on the concept of the symmetry group of a path and are develop a code (to be made publicly available when ready) to implement these ideas in Quantum Espresso, an open-source density functional theory (DFT) software. Three model system classes are picked, namely, in simple perovskites, in layered oxides, and in multiferroics, to make predictions. The predicted MEPs with this approach are tested using the experimental techniques that push in-situ dynamics with 2-5 picometers metrology in electron microscopy, and ultrafast electron diffraction microscopy techniques.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.