A Symmetry-Based Approach to Minimum Energy Pathways

非技术描述：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，对于理解原子在场、温度和应力等外部刺激下运动的一系列动力学材料过程非常重要。预测材料在经历扭曲时会走哪条路径，对于任何涉及这种原子运动的应用都很重要。然而，预测这样的路径，称为最小能量路径(MEP)，目前本质上是随机的，人们永远不能确定最终结果。这个项目的目的是通过引入扭曲-反转对称性和扭曲群等新概念来开发一个新的基于对称性的框架和计算工具；它显著地提高了搜索这类路径的速度、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。计算材料研究方面日益增长的教育培训需求正在通过密度泛函理论实践讲习班、对包括女性和代表性不足群体在内的本科生的积极指导，以及通过积极参与STEM向上界限数学和科学计划以及宾夕法尼亚州立大学千年学者计划来解决，该计划吸引并引导有才华的STEM学生进入本科生计划。技术描述：这是一个综合的理论-实验方案，开发了新的对称性概念和计算工具，以探索扭曲的最小能量路径(MEP)，更具体地说，探索铁电磁畴转换和磁畴壁运动的最小能量路径。MEP的计算采用推式弹性带方法(NEB)，但目前它依赖于随机过程和用户直觉相结合的方法来构造初始路径。主要研究人员专注于路径对称群的概念，并正在开发代码(准备好后公开提供)，以在开源密度泛函理论(DFT)软件Quantum Espresso中实现这些想法。选择了三个模型系统类，即简单钙钛矿模型、层状氧化物模型和多铁性模型进行预测。使用这种方法预测的MEP使用实验技术进行测试，这些实验技术推动了电子显微镜中2-5皮米计量的原位动力学，以及超快电子衍射显微镜技术。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.