First Principles Computational Study of Defects, Diffusion and Grain Boundaries in Mantle Materials

地球材料研究的主要挑战之一是建立一个坚实的理论基础来理解硅酸盐和氧化物材料在高压-高温条件下的流变特性。流变学是控制地震观测和其他来源暗示的复杂地幔动力学的关键因素。例如，地幔可能变形的不同机制（扩散或位错蠕变）意味着地幔动力学的截然不同的图景。尽管最近在扩散和变形实验方面取得了进展，但将测量数据应用于深部地幔条件仍然需要大量的外推。PI和合作者先前已经证明，第一原理方法（基于密度泛函理论）是一种无参数的方法，为实验提供了理想的补充。在这个项目中，他们将计算和可视化方法相结合，进一步促进我们对关键相关属性的理解。具体活动包括：1)将点缺陷的研究扩展到包括地幔矿物中的杂质（包括质子）和缺陷复合物。缺陷能量学对我们理解矿物中的扩散和变形是至关重要的。2)研究晶界及其对缺陷形成和迁移的影响。原生缺陷和杂质的晶界偏析是特别有趣的。3)可视化模拟数据，以深入了解缺陷核心的结构（键合和配位）、微观机制（与杂质掺入和扩散有关）和电子性质（缺陷状态和相关的电子定位/捕获）。研究人员预计，预测结果将对地幔变形的性质、地球内部的地球化学过程和离子对地幔电导率的贡献具有重要意义。同时，他们希望丰富理论与实验的联系。该方案旨在系统地弥合计算科学与地球材料研究之间的差距，有效地利用高端并行超级计算和可视化。它的成功完成将对包括地球物理、材料物理和计算科学在内的许多领域产生影响。研究结果将通过地球科学和物理学科的出版物以及计算/计算机科学会议记录进行传播。最后，该提案为培训新科学家在多个领域积累经验和专业知识提供了一个独特的机会。

One of the major challenges in Earth materials research is to develop a firm theoretical basis to understanding the rheological properties of the silicate and oxide materials at high pressure-high temperature conditions. Rheology is a key factor, which controls the complicated mantle dynamics implied by seismological observations and other sources. For instance, the different mechanisms (diffusion or dislocation creep) by which the mantle may deform imply profoundly different pictures of mantle dynamics. Despite recent progress in diffusion and deformation experiments, large extrapolations are still needed to apply the measured data to deep mantle conditions. The PI and collaborators have previously demonstrated that first principles methods (based on density functional theory) being a parameter free approach provide an ideal complement to experiments. In this project, they apply a combination of computational and visualization methods to further promote our understanding of key relevant properties. Specific activities include: 1) Extending the study of point defects to include impurities (including protons) and complexes of defects in mantle minerals. Defect energetics is essential to our understanding of diffusion and deformation in minerals. 2) Investigating grain boundaries and their influence on defect formation and migration. The grain boundary segregation of native defects and impurities is of particular interest. 3) Visualizing simulation data to gain insight into the structures (bonding and coordination) of defect cores, microscopic mechanisms (related to impurity incorporation and diffusion), and electronic properties (defect states and associated localization/trapping of electrons). The investigators anticipate that the predicted results will have important implications for the nature of mantle deformation, geochemical processes in the Earth's interior and ionic contribution to mantle conductivity. Also, they hope to enrich contact between theory and experiment. The proposal aims to systematically bridge the gap between computational science and Earth materials research and exploit high-end parallel supercomputing and visualization effectively. Its successful completion will have impact on a number of fields including geophysics, materials physics and computational science. The results will be disseminated through publications in geosciences and physics disciplines as well as computational/computer science conference proceedings. Finally, the proposal represents a unique opportunity for training new scientists to develop experience and expertise in more than one area.