First-Principles Molecular Dynamics Simulations of Silicate Liquids: Structure, Diffusion and Viscosity at Mantle Conditions

已知硅酸盐液体在行星演化和岩浆海洋中起着重要作用。岩浆作用是大洋地壳和大陆地壳起源和持续形成的原因，也是将我们了解地球内部组成的主要线索之一以捕虏体的形式带到地表的原因。由于硅酸盐液体和它们的源区在密度、化学扩散率、粘度和体积组成上的差异，岩浆的生成和迁移是物质和热量迁移的最有效的地质手段之一。硅酸盐液体可能在地球上发挥了更重要的作用？的早期历史。地球热历史模型和对古代样品的岩石学研究表明，熔融可能更广泛，可能延伸到更深的地方。 由于它们对地球化学和地球动力学过程的强烈影响，更好地了解行星演化需要我们在地幔条件下相关熔体性质的知识方面取得重大进展。在该项目中，建议应用第一性原理计算和可视化技术的组合来研究硅酸盐熔体在广泛的压力、温度和组成范围内的结构、扩散和粘度。这种类型的方法，是参数自由的性质，预计将提供理想的补充实验方法，并提供重要的洞察力的基本起源的物理性质和行为的结构和键合。这项研究的目标之一是扩大成分范围，包括一个模型玄武岩系统（透辉石-钙长石）。密度，焓，和结构作为压力和温度的函数的理论结果，预计将提高我们的理解的浮力，键合，多态性，和热力学混合硅酸盐液体。此外，计划通过自扩散系数和粘度的从头算预测来研究硅酸盐熔体的输运性质。原子可视化的位置-时间序列数据将被利用，以深入了解运输和压缩的微观机制，并进入温度，压力和成分的扩散的依赖性。硅酸盐玻璃的结构和压缩机制的研究是一个有价值的方法，以获得更多的洞察力的能量学基础的液体结构，并丰富与广泛的实验文献地质相关的组合物在玻璃态的接触。因此，该提案的一个统一主题是大型系统的第一性原理计算机模拟，这对于探索现实的熔体组成，准确计算动力学特性以及成功捕获玻璃结构的本质是必要的。该项目将对地球化学、岩石学、岩石物理学、计算材料物理学和科学可视化等多个领域产生影响，并将培养新的科学家，使其具备多学科的专业知识。

Silicate liquids are known to play an important role in planetary evolution and magma oceans. Magmatic processes are responsible for the origin and ongoing formation of the oceanic and continental crust, and for bringing to the surface one of our primary clues to the composition of the Earth's interior in the form of xenoliths. Because of the contrast in density, chemical diffusivity, viscosity, and bulk composition between silicate liquids and their source regions, the generation and transport of magma is one of the most efficient geological means of mass and heat transport. Silicate liquids may have played an even more important role in the Earth?s earlier history. Models of the Earth's thermal history and petrological studies of ancient samples suggest that melting may have been more widespread and may have extended to greater depths. Because of their strong influence on geochemical and geodynamical processes, a better understanding of planetary evolution requires major advances in our knowledge of relevant melt properties at mantle conditions. In this project, it is proposed to apply a combination of first-principles computational and visualization techniques to investigate structure, diffusion and viscosity of silicate melts over a broad range of pressure, temperature and composition. This type of approach, being parameter free in the nature, is expected to provide the ideal complement to the experimental approach and provide important insight into the fundamental origins of physical properties and behavior in structure and bonding. One of the goals of the study will be to expand the range of compositions to include a model basalt system (diopside-anorthite). Theoretical results on the density, enthalpy, and structure as a function of pressure and temperature are expected to enhance our understanding of buoyancy, bonding, polymorphism, and thermodynamics of mixing in silicate liquids. In addition, it is planned to investigate transport properties of silicate melts through ab initio predictions of the self-diffusion coefficients and viscosities. Atomistic visualization of the position-time series data will be exploited to gain insight into the microscopic mechanisms of transport and compression, and into dependence of diffusion on temperature, pressure and composition. Studies of the structure and compression mechanisms of silicate glasses are a valuable approach to gain additional insights into the energetics underlying liquid structure, and to enrich contact with the extensive experimental literature on geologically relevant compositions in the vitreous state. A unifying theme of the proposal is thus the first-principles computer simulations of large systems that are necessary to explore realistic melt compositions, to accurately compute dynamical properties and to successfully capture the essence of glass structures. The project will have impact on a number of fields including geochemistry, petrology, geophysics, computational materials physics, and scientific visualization, and it will train new scientists to have a multidisciplinary expertise.