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

Louisiana State University, Baton Rouge LA

Investigators

Abstract

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.