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

硅酸盐液体是地球化学和热演化的主要媒介，因为它们形成早期岩浆海洋，并在地球表面以岩浆形式出现，在地壳和地幔中以部分熔融形式出现。岩浆作用是大洋地壳和大陆地壳起源和持续形成的原因，也是将我们以捕虏体形式了解内部组成的主要线索之一带到地表的原因。由于硅酸盐液体和它们的源区之间在密度、化学扩散性、粘度和体积组成上的差异，岩浆的生成和运输是导致质量和热量运输的最有效的地质过程之一。硅酸盐液体可能在地球早期历史中发挥了更重要的作用，当时熔融可能更广泛，并可能延伸到更深的地方。 因此，更好地了解行星的演化需要我们在地幔压力-温度条件下的相关熔体性质的知识的重大进展，在这个项目中，我们建议应用第一性原理计算和可视化技术相结合，以研究在广泛的压力，温度和组成范围内的硅酸盐熔体的结构，扩散和粘度。这种方法，是参数自由的性质，预计将提供理想的补充实验方法，并可以提供重要的见解的基本物理性质和行为的结构和键合。提议的具体活动包括：1）扩大成分范围，以便对不含挥发物（H2O和CO2）的天然熔体（MgO-CaO-Na 2 O-K2 O-Al 2 O3-TiO 2-SiO2系统）进行取样。计算出的密度，hippies，和结构作为压力和温度的函数，预计将提高我们的理解的浮力，键合，挥发性组分的形态，多态性，和热力学的混合在多组分熔体系统。2)通过自扩散系数和粘度系数的第一性原理预测研究硅酸盐熔体的输运性质。位置-时间序列的原子可视化将使我们能够深入了解压缩和传输现象的微观机制，以及扩散/粘度对温度，压力和成分的复杂依赖关系。3)继续硅酸盐玻璃的结构和压缩机制的研究，以获得更多的洞察力的能量学基础液体结构的方式，并为了丰富与广泛的实验文献在玻璃态地质相关的组合物的接触。该提案的统一主题是探索现实成分所需的大型系统的第一性原理模拟，以准确计算动力学特性并成功捕捉玻璃结构的本质。PI可以在当地获得足够的资源来进行这种密集的模拟。 该研究实质上是利用计算科学的思想和技术来解决地球物质研究中的挑战性问题。它将对许多领域产生影响，包括地球化学，岩石学，矿物物理学，计算矿物/材料物理学和科学可视化，并将培养学生拥有多学科的经验和专业知识。

Silicate liquids are primary agents of chemical and thermal evolution in the Earth as they form early magma ocean, and appear as magmas in the surface of the planet and as partial melts in the crust and mantle. 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 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 among the most efficient geological processes leading to mass and heat transport. Silicate liquids may have played an even more important role in the Earth's early history when melting may have been more widespread and may have extended to greater depths. A better understanding of planetary evolution thus requires major advances in our knowledge of relevant melt properties at mantle pressure-temperature 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 broad range of pressure, temperature and composition. This approach, being parameter free in the nature, is expected to provide the ideal complement to experimental approaches, and can provide important insights into the fundamental physical properties and behavior in structure and bonding. The specific activities proposed include: 1) Expanding the range of composition towards sampling natural melts (MgO-CaO-Na2O-K2O-Al2O3-TiO2-SiO2 system) with/out volatiles (H2O and CO2). The calculated densities, enthalpies, and structures as a function of pressure and temperature are expected to enhance our understanding of buoyancy, bonding, speciation of volatile components, polymorphism, and thermodynamics of mixing in a multi-component melt system. 2) Investigating the transport properties of silicate melts through first-principles predictions of the self-diffusion and viscosity coefficients. Atomistic visualization of the position-time series will allow us gain insight into the microscopic mechanisms of compression and transport phenomena, and into the complex dependence of diffusion/viscosity on temperature, pressure and composition. 3) Continuing the study of structure and compression mechanisms of silicate glasses as a way of gaining additional insight into the energetics underlying liquid structure, and in order to enrich contact with the extensive experimental literature on geologically relevant compositions in the vitreous state. The unifying theme of the proposal is the first-principles simulations of large systems needed to explore realistic compositions, to accurately compute dynamical properties and to successfully capture the essence of glass structures. The PI has local access to sufficient resources to carry out such intensive simulations. The proposed research is essentially an exploitation of ideas and techniques of computational science to challenging problems in the investigation of Earth materials. It will have impact on a number of fields including geochemistry, petrology, geophysics, computational mineral/materials physics, and scientific visualization, and it will train students to have a multidisciplinary experience and expertise.