Ab initio phonon models of lattice thermal conductivity of lower mantle minerals

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The Earth's internal heat drives plate tectonics at the surface, convection within the mantle, and the magneto hydrodynamics in the core. However, the total heat flow across the core-mantle boundary (CMB), a crucial component of the global heat budget, remains poorly constrained, because laboratory thermal transport experiment can not yet directly access the relevant high temperature/pressure conditions, and long extrapolations of measured data at lower temperatures/pressures results in large uncertainties in previous estimates of thermal conductivity of the thermal boundary layer right above the CMB. Atomic scale calculations and simulations based on the first-principles quantum theories provide a complimentary approach to determine the lattice thermal conductivity of iron bearing lower mantle mineral solid solutions. The proposed study is made possible by the availability of large parallel supercomputers and the successful algorithm/data-structure parallelization and optimization by the investigator's group. Not only the new first-principles computer models will improve the constraints on the estimated CMB heat flow, the calculated results will also help us to understand microscopic heat conduction processes in the complex materials systems and therefore reveal the basic physics of heat transport at extreme conditions. The computational methodology development in this study can be adopted to study other complex materials systems, such as novel thermoelectric materials. The training of graduate students in solid-state physics, geophysics, and high-performance computing will provide a well-rounded interdisciplinary education for the next-generation computational mineral physicists.Specifically, theoretical models of thermal conductivity of the Earth's lower mantle will be proposed, anchored on robust first-principles models of temperature, pressure, and iron concentration/spin-state dependences of lattice thermal conductivity in four major lower mantle mineral groups, including ferropericlase, Fe-bearing perovskite and post-perovskite MgSiO3, cubic CaSiO3 perovskite, derived using the newly implemented first-principles computational method that combines density functional theory and the kinetic phonon transport theory. The first-principles theoretical data will be formulated and tabulated in the formats that can be easily adopted by geodynamical simulations and/or other Earth Sciences applications that require thermal transport data. In addition, the new theoretical models will be benchmarked with latest experimental data (1) to validate and further improve empirical temperature-pressure extrapolation models for thermal transport properties, and (2) to explore new heat conduction mechanisms at extremely high temperatures.