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

众所周知，硅酸盐液体在行星演化和岩浆海洋中发挥着重要作用。岩浆作用负责大洋和大陆地壳的起源和持续形成，并以捕虏体的形式将我们关于地球内部组成的主要线索之一带到地表。由于硅酸盐液体与其源区在密度、化学扩散率、粘度和体积组成等方面的差异，岩浆的生成和输运是最有效的物质和热输运的地质手段之一。硅酸盐液体可能在地球更早的历史上发挥了更重要的作用？S。对地球热史的模型和对古代样品的岩石学研究表明，熔融可能更广泛，可能已经延伸到更深的地方。由于它们对地球化学和地球动力学过程的强烈影响，要更好地理解行星的演化，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。在这个项目中，建议应用第一性原理计算和可视化技术相结合的方法来研究在广泛的压力、温度和组成范围内硅酸盐熔体的结构、扩散和粘度。这种方法本质上是无参数的，有望为实验方法提供理想的补充，并为结构和成键中物理性质和行为的基本起源提供重要的见解。这项研究的目标之一将是扩大成分范围，将模型玄武岩系统(透辉石-斜长岩)包括在内。关于密度、热焓和结构随压力和温度的变化的理论结果有望加深我们对硅酸盐液体中混合的浮力、成键、多晶性和热力学的理解。此外，还计划通过从头计算自扩散系数和粘度来研究硅酸盐熔体的输运性质。将利用位置-时间序列数据的原子可视化来深入了解传输和压缩的微观机制，以及扩散对温度、压力和成分的依赖。研究硅酸盐玻璃的结构和压缩机制是深入了解液体结构背后的能量学的有价值的途径，并丰富了与玻璃状态下地质相关成分的广泛实验文献的联系。因此，该提案的一个统一主题是对大系统的第一原理计算机模拟，这对于探索真实的熔体组成、准确计算动力学性质和成功捕捉玻璃结构的本质是必要的。该项目将对地球化学、岩石学、地球物理、计算材料物理和科学可视化等多个领域产生影响，并将培养具有多学科专业知识的新科学家。

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.