Collaborative Research: First Principles Investigation of Silicate Liquids at Mantle Conditions

该项目将应用基于密度泛函理论(DFT)的第一性原理方法来研究硅酸盐液体的物理化学性质，硅酸盐液体是地幔的主要组成部分。这种方法已经被证明是研究地球材料广泛结晶性质的实验方法的理想补充，在这里它将被扩展到涉及相对大量原子的材料系统的模拟。这些大规模的模拟将导致我们在压力、温度和组成的大范围内对硅酸盐液体的了解取得重大进展，这些对更好地理解行星演化至关重要，因为硅酸盐液体是地球内部热量和质量传输的主要手段。该项目将对理解：a)通过从头算预测包括透辉石、顽辉石和镁橄榄岩组成的液体在地幔压力-温度区域的状态方程，了解硅酸盐液体的浮力；b)通过分析理论模拟中可用的完整结构信息，包括配位数、键长和键角，来分析硅酸盐液体的结构。通过对透辉石和含水钠长石组成液体的结构分析，以及对镁硅熔点上熔体结构的分析，有望深入了解熔体行为的起源，包括压缩机制和混合性质；以及c)通过从头算预测混合在硅酸盐液体中的体积和混合热作为沿镁硅和钠长石-水连接的组成的函数，从而深入了解熔体行为的起源。这项拟议的研究实质上是利用计算科学的思想和技术来挑战地球材料调查中的问题。一方面，复杂的地球化学和地球材料问题的研究之间的交叉，另一方面，高端计算应该对这两个领域都有好处。为了充分利用这方面的优势，该项目还将启动Access Grid的应用，这是一种允许组对组多媒体网络通信的设施，以培训学生进行这一跨学科努力。

The project will apply the first-principles approach based on density functional theory (DFT) to investigate the physico-chemical properties of silicate liquids, which are major components of the Earth's mantle. The approach has already been proven to be an ideal complement to the experimental approach in studying a wide range of crystalline properties of the Earth materials and here it will be extended to simulation of material systems involving relative large number of atoms. These large-scale simulations will result in major advances in our knowledge of silicate liquids over the large range of pressure, temperature, and composition that are crucial for a better understanding of planetary evolution, as silicate liquids are primary means of heat and mass transport inside the Earth. The project will make key contributions to understanding of: a) Buoyancy of silicate liquids through ab initio predictions of the equation of state including liquids of diopside, enstatite, and forsterite compositions over the pressure-temperature regime of the mantle; b) Structure of silicate liquids via analysis of the complete structural information that is available in theoretical simulations including coordination numbers, bond lengths, and bond angles. Analysis of the structure of liquids of diopside and hydrous albite composition, and melts on the MgO-SiO2 join is expected to yield insight into the origin of melt behavior including compression mechanisms and mixing properties; and c) Thermodynamics of mixing in silicate liquids through ab initio predictions of the volume and enthalpy of mixing as a function of composition along the MgO-SiO2 and albite-water joins. The proposed research is essentially an exploitation of ideas and techniques of computational science to challenging problems in the investigation of Earth materials. The cross-fertilization between studies of complex geochemical and earth materials issues on the one hand, and high-end computation on the other should be of benefit to both fields. To take full advantage of this aspect, the project will also initiate applications of the Access Grid - a facility that allows group-to-group multimedia network communication, to train students in this interdisciplinary effort.