Prediction and characterization of novel Earth-forming minerals using advanced ab initio simulations

使用先进的从头算模拟对新型地球形成矿物进行预测和表征

• 批准号: 1114313
• 负责人: Artem Oganov
• 金额: $ 36万
• 依托单位: SUNY at Stony Brook
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-09-01 至 2015-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1114313&HistoricalAwards=false
• 关键词: Prediction; characterization; novel; Earth; forming

The study of the Earth's deep interior is one of the most fascinating fields of modern research. It expands our knowledge about the world in which we live and provides clues for understanding processes that have shaped our planet and determine phenomena that we observe on the surface of the Earth such as the magnetic field of the Earth, volcanism, earthquakes, etc. Our understanding of the deep Earth comes from a number of different sources, including: 1) geophysical observations, mainly seismology and geomagnetic observations ,2) mineral physics, 3) numerical modeling of the Earth?s dynamics and energetics,4) geochemistry and cosmochemistry, and 5) direct (but, unfortunately, limited) evidence from the deep mantle from inclusions in diamonds. Mineral physics provides information about the physical properties of Earth forming minerals, their dependence on temperature and composition, and phase diagrams of mineral systems. Mineral physics information is used to explain seismic discontinuities, deduce the composition and temperature inside the Earth, interpret the origins of seismic anisotropy. While experimentally it is possible to reach conditions of the Earth's innermost core, such studies are extremely complicated and have significant uncertainties in the measurements of pressure, temperature, and physical properties, many of which can not yet even be measured at all. In this situation, theoretical simulations based on quantum mechanics and making no assumptions about the nature of the material, have already proven their utility in Earth sciences, in particular, in combination with experiment. Among many important advances made using quantum-mechanical calculations are the establishment of the crystal structure of MgSiO3 perovskite, discovery and characterization of MgSiO3 post-perovskite, and the determination of the melting curve of iron. The discovery of post-perovskite has provided, for the first time, a simple convincing explanation for seismic anomalies found in the D" layer of the Earth mantle and uncovered fascinating insights into the structure, dynamics, and evolution of our planet. For instance, it explained the unusually large topography of the D" discontinuity and showed that the D" layer is growing with time as the Earth cools down. The existence of the post-perovskite phase transition in the deep mantle has been shown to lead to important geodynamical consequences. The large contrast of rheological properties between perovskite and post-perovskite may also have important geodynamical implications. The post-perovskite phase transition provided tighter constraints on the temperature profile in the mantle, the heat flow from the core into the mantle, and explained the double discontinuity found near the boundary with the core. The melting curve of iron, on the other hand, helped researchers to constrain the temperature profile in the Earth's core. Despite these breakthroughs, Earth's inner core and core-mantle boundary remain mysterious regions with major unsolved questions. The present project aims at clarifying these questions. Ths investigators will apply the most advanced and recently developed tools in computational physics - in particular, evolutionary crystal structure prediction (Oganov, Glass, 2006) to address outstanding problems related to the inner core and core-mantle boundary region.(i) From crystal chemistry of alloys to the chemistry of the inner core. Usually, compositional models of the inner core start from equations of state of FeSi, FeS or Fe3S, Fe1-xO, Fe3C or Fe7C3, and FeH - which are assumed to be the stable compounds in the corresponding binary systems. Except FeSi, none of these compounds were proved (either experimentally or theoretically) to be stable at the actual conditions of the inner core. The actually stable compounds may have different chemistry, coordination numbers, density and elasticity, and this may lead to serious changes in compositional models of the inner core. (ii) Properties of alloys in the inner core. Once we predict the stable compositions and structures, equations of state and elastic constants will be computed taking into account the effects of pressure and temperature. Anomalous anisotropy and high Poisson ratio may then be perhaps explained by the properties of iron alloys. (iii) Reaction at the core-mantle boundary: what could be its products? There are proposals of various chemical reactions occurring at the core-mantle boundary. Such a reaction could have important geophysical implications, and the PI would like to approach this possibility theoretically/computationally by exploring chemical equilibria in the relevant multicomponent system(s). While direct exploration of all possible reactions in this system is overwhelmingly difficult, new computational tools may enable rapid exploration.

对地球内部深处的研究是现代研究中最令人着迷的领域之一。它扩展了我们对我们生活的世界的了解，并为理解塑造我们星球的过程提供了线索，并确定了我们在地球表面观察到的现象，如地球磁场，火山活动，地震等。1）地球物理观测，主要是地震和地磁观测; 2）矿物物理;的动力学和能量学，4）地球化学和宇宙化学，和5）直接（但不幸的是，有限的）证据，从深地幔中的钻石包裹体。矿物物理学提供有关地球形成矿物的物理性质，它们对温度和成分的依赖以及矿物系统的相图的信息。利用矿物物理信息解释地震不连续性，推断地球内部的成分和温度，解释地震各向异性的成因。虽然实验上有可能达到地球最内核的条件，但这种研究非常复杂，并且在压力，温度和物理特性的测量中具有很大的不确定性，其中许多甚至根本无法测量。在这种情况下，基于量子力学的理论模拟，不对材料的性质做任何假设，已经证明了它们在地球科学中的实用性，特别是与实验相结合。使用量子力学计算取得的许多重要进展包括MgSiO 3钙钛矿晶体结构的建立，MgSiO 3后钙钛矿的发现和表征，以及铁的熔化曲线的测定。后钙钛矿的发现首次为地幔D”层中发现的地震异常提供了一个简单而令人信服的解释，并揭示了对地球结构、动力学和演化的迷人见解。例如，它解释了D”不连续的异常大的地形，并表明随着地球冷却，D”层随着时间的推移而增长。地幔深部后钙钛矿相变的存在已被证明会导致重要的地球动力学后果。钙钛矿和后钙钛矿之间的流变学性质的巨大差异也可能具有重要的地球动力学意义。后钙钛矿相变提供了更严格的限制，在地幔中的温度分布，从核心到地幔的热流，并解释了双不连续附近的边界与核心。另一方面，铁的熔化曲线帮助研究人员限制了地核的温度分布。尽管有这些突破，地球的内核和地核-地幔边界仍然是神秘的区域，有许多未解决的问题。本项目旨在澄清这些问题。研究人员将应用计算物理学中最先进和最新开发的工具-特别是演化晶体结构预测（Oganov，Glass，2006），以解决与内核和核幔边界区域相关的突出问题。(i)从合金的晶体化学到内核的化学。通常内核的组成模型是从FeSi、FeS或Fe 3S、Fe 1-xO、Fe 3C或Fe 7 C3和FeH -的状态方程出发的，它们被认为是相应二元系统中的稳定化合物。除了FeSi，这些化合物都没有被证明（无论是实验还是理论）在内核的实际条件下是稳定的。实际上稳定的化合物可能具有不同的化学性质、配位数、密度和弹性，这可能导致内核的组成模型发生严重变化。(ii)内核中合金的特性。一旦我们预测了稳定的组成和结构，状态方程和弹性常数将被计算，并考虑到压力和温度的影响。反常的各向异性和高泊松比也许可以用铁合金的性质来解释。(iii)核幔边界反应：其产物可能是什么？有各种化学反应发生在核幔边界的建议。这种反应可能具有重要的地球物理意义，PI希望通过探索相关多组分系统中的化学平衡，从理论/计算上探讨这种可能性。虽然直接探索这个系统中所有可能的反应是极其困难的，但新的计算工具可以实现快速探索。