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

硅酸盐液体的第一原理分子动力学模拟：地幔条件下的结构、扩散和粘度

• 批准号: 1426530
• 负责人: Bijaya Karki
• 金额: $ 36万
• 依托单位: Louisiana State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-08-01 至 2018-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1426530&HistoricalAwards=false
• 关键词: First; Principles; Molecular; Dynamics; Simulations

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.

岩浆作用被认为在地球的化学和热演化中起着重要作用。它们负责海洋和大陆地壳的起源和持续形成。它们可能在地球上扮演了更重要的角色？在早期的历史中，增生的地球可能大部分或完全熔化？所谓的岩浆海洋。熔融物也被认为存在于现今地球的浅层岩浆成因带之下，包括过渡带和核幔边界的顶部。这些岩浆和熔体主要由硅酸盐物质组成。为了了解这些深熔体的起源和稳定性，以及它们在地球最早期演化和地震观测解释中的作用，必须了解硅酸盐液体在相关压力、温度和成分的广泛范围内的物理性质。地球极端条件下硅酸盐液体的研究？的内部构成了巨大的挑战。在这里，我们建议应用第一原理并行计算和可视化技术的组合来解决这个复杂的硅酸盐液体系统。我们的方法是无参数的实验提供了理想的补充。 为了进一步加深对硅酸盐液体在行星演化和岩浆过程中的作用的理解，我们计划开展以下具体活动：1）考虑更多的成分，对天然熔体（MgO-CaO-FeO-Fe 2 O 3-Na 2 O-K 2 O-Al 2 O 3-TiO 2-SiO 2系统）进行取样，有/没有挥发分（H 2 O和CO 2），以计算它们的密度、饱和度和结构作为压力和温度的函数。2)通过对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。3)继续研究硅酸盐玻璃的结构和压缩机制，作为进一步了解液体结构背后的能量学的一种方式，并丰富与玻璃态地质相关成分的广泛实验文献的联系。4)可视化/分析大量模拟数据，深入了解压缩和传输现象的微观机制。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，这对于探索现实的熔体组成，准确预测关键的传输特性以及成功捕获玻璃结构的本质是必要的。这些结果将使我们能够定量地了解熔融硅酸盐和它们的源区之间的密度，扩散率，粘度和体积组成的对比，这些源区控制着岩浆和部分熔体的生成和运输。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。这种协同作用将对地球化学、岩石学、地球物理学、计算材料物理学和科学可视化等领域产生影响。它将培养研究生和本科生，以及博士后这一多学科的经验和专业知识。