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

岩浆过程被认为在地球的化学和热演化中起着重要的作用。它们对海洋和大陆地壳的起源和持续形成负有责任。它们可能在地球上扮演了更重要的角色？在早期的历史中，不断增生的地球可能大部分或完全处于熔融状态。这就是所谓的岩浆海。熔体也被认为存在于当今地球上远低于浅岩浆成因带的深处，包括过渡带顶部和核心-地幔边界。这些岩浆和熔体基本上由硅酸盐物质组成。为了了解这些深层熔体的起源和稳定性，以及它们在地球早期演化中的作用和对地震观测结果的解释，了解硅酸盐液体在相关的压力、温度和组成的广泛范围内的物理性质是必不可少的。地球极端条件下硅酸盐液体的研究？美国的内部构成了巨大的挑战。在这里，我们建议结合第一性原理并行计算和可视化技术来解决这个复杂的硅酸盐液体系统。我们的方法无参数，为实验提供了理想的补充。为了进一步加深我们对硅酸盐液体在行星演化和岩浆过程中的作用的认识，我们计划开展以下具体活动：1)考虑更多的成分来取样天然熔体（MgO-CaO-FeO-Fe2O3-Na2O-K2O-Al2O3-TiO2-SiO2体系）的挥发分（H2O和CO2），计算它们的密度、焓和结构与压力和温度的关系。2)通过自扩散和黏度系数的第一性原理预测研究硅酸盐熔体的输运性质。3)继续研究硅酸盐玻璃的结构和压缩机制，以进一步了解液体结构下的能量学，并丰富与玻璃体状态下地质相关成分的大量实验文献的联系。4)可视化/分析海量模拟数据，深入了解压缩和输运现象的微观机制。因此，该提案的一个统一主题是对大型系统进行密集的第一性原理计算机模拟，这对于探索真实的熔体成分、准确预测关键输运性质以及成功捕获玻璃结构的本质是必要的。这些结果将使我们定量地了解熔融硅酸盐及其源区之间的密度、扩散率、粘度和体积组成的差异，这些差异控制着岩浆和部分熔体的产生和运输。提出的研究本质上是利用计算科学的思想和技术来挑战地球材料研究中的问题。这种协同作用将对许多领域产生影响，包括地球化学、岩石学、地球物理、计算材料物理学和科学可视化。它将培养研究生、本科生和博士后具备多学科经验和专业知识。

Magmatic processes are considered to play important role in the chemical and thermal evolution of the Earth. They are responsible for the origin and ongoing formation of the oceanic and continental crust. They may have played even more important role in the Earth?s earlier history when the accreting Earth may have been largely or completely molten ? so called the magma ocean. Melts are also thought to exist in the present day Earth at depths well below the shallow magma genetic zone, including atop the transition zone and the core-mantle boundary. These magmas and melts are essentially composed of silicate materials. To understand the origin and stability of these deep melts, and their role in the earliest evolution of the Earth and in the interpretation of seismic observations, knowledge about the physical properties of silicate liquids over relevant broad ranges of pressure, temperature, and composition is essential. Investigation of silicate liquids at extreme conditions of the Earth?s interior poses tremendous challenges. Here, we propose to apply a combination of first-principles parallel computation and visualization techniques to tackle this complex silicate liquid system. Our approach being parameter free provides the ideal complement to the experiments. To further promote our understanding of the role of silicate liquids in planetary evolution and magmatic processes, we plan to carry out the following specific activities: 1) Consider more compositions towards sampling natural melts (MgO-CaO-FeO-Fe2O3-Na2O-K2O-Al2O3-TiO2-SiO2 system) with/out volatiles (H2O and CO2) to calculate their densities, enthalpies, and structures as a function of pressure and temperature. 2) Investigate the transport properties of silicate melts through first-principles predictions of the self-diffusion and viscosity coefficients. 3) Continue 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. 4) Visualize/analyze the massive simulation data to gain insight into the microscopic mechanisms of compression and transport phenomena. A unifying theme of this proposal is thus the intensive first-principles computer simulations of large systems that are necessary to explore realistic melt compositions, to accurately predict key transport properties, and to successfully capture the essence of glass structures. These results will allow us quantitatively understand the contrasts in density, diffusivity, viscosity, and bulk composition between molten silicates and their source regions, which control the generation and transport of magma and partial melts. The proposed research is essentially an exploitation of ideas and techniques of computational science to challenging problems in the investigation of Earth materials. This synergy will have impact on a number of fields including geochemistry, petrology, geophysics, computational materials physics, and scientific visualization. It will train graduate and undergraduate students, and postdoc for this multidisciplinary experience and expertise.