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为了解硅酸盐和氧化物材料在高压高温条件下的流变性奠定坚实的理论基础。流变性是一个关键因素，它控制着地震观测和其他来源所隐含的复杂的地幔动力学。例如，地幔变形的不同机制(扩散或位错蠕动)意味着地幔动力学的深刻不同图景。尽管最近在扩散和变形实验方面取得了进展，但仍需要进行大量的外推，才能将测量数据应用于深部地幔条件。PI及其合作者此前已经证明，第一性原理方法(基于密度泛函理论)是一种无参数方法，为实验提供了理想的补充。在这个项目中，他们应用了计算和可视化方法的组合，以进一步促进我们对关键相关属性的理解。具体活动包括：1)扩大对点缺陷的研究，包括地幔矿物中的杂质(包括质子)和缺陷络合物。缺陷能量学对于我们理解矿物中的扩散和变形是必不可少的。2)研究晶界及其对缺陷形成和迁移的影响。本征缺陷和杂质的晶界偏析尤其令人感兴趣。3)可视化模拟数据，以深入了解缺陷核的结构(键合和配位)、微观机制(与杂质的结合和扩散有关)和电子性质(缺陷态和相关的电子局域化/陷阱)。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以及离子对地幔传导性的贡献产生重要影响。此外，他们还希望丰富理论与实验之间的联系。该提议旨在系统地弥合计算科学和地球材料研究之间的差距，并有效地开发高端并行超级计算和可视化。它的成功建成将对地球物理、材料物理和计算科学等多个领域产生影响。这些成果将通过地球科学和物理学科的出版物以及计算/计算机科学会议论文集传播。最后，该提案为培训新科学家提供了一个独特的机会，使他们能够在多个领域积累经验和专业知识。

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.