| 英文摘要: | Humans have greatly advanced in the study of the outer space and inner workings of atomic matter, but the very planet upon which we live remains a mystery. Hidden from us and impossible to probe directly, Earth's deep interior has defined the face our planet and profoundly influences our daily life (through earthquakes, volcanism, and the magnetic field that saves life from solar wind). Progress in studies of the Earth's deep interior can only be made through a combination of seismology, geochemistry, and mineral physics. Computational mineral physics has made great progress recently, with the development of quantum-mechanical methods allowing one to study complex chemistry pertinent to the Earth, and make unbiased predictions of novel chemical phenomena that take place under high pressures and temperatures typical of planetary interiors. This project aims toward a better understanding Earth's chemistry and physics with the help of advanced quantum-mechanical methods. Such methods are quite universal and recently have led to breakthroughs in the computational design of novel materials, which have a potentially transformative value for our society. This research bridges several the fields of geosciences, materials science, physics, and chemistry, and focuses on problems that excite curiosity of humans ("what is the Earth made of", "how was the Earth formed"). Such studies are impossible without the energy of young scientists who will get unique training in this multidisciplinary field of science and will be perfectly equipped to serve the world in any of these fields.
The study of the Earth's deep interior is one of the most fascinating fields of modern research. Currently, based on several decades continuing works by geoscientists, reasonable mineralogical models of the deep Earth are finally constructed. Thermal and compositional variations in the deep Earth can be well estimated by data from seismic tomography and mineral physics. Mineral physics provides information about the physical properties of Earth-forming minerals together with their dependence on temperature and composition, and phase diagrams of mineral systems. Exploration of the Earth-forming minerals is one of the most critical issues in Earth sciences. Despite tremendous progress in experimental high-pressure techniques, most physical measurements at pressures of the Earth's deep mantle and core are problematic. Recently, (Mg,Fe)SiO3 perovskite, long believed to be stable in the Earth's deep lower mantle, was found to decompose into MgSiO3 perovksite and an Fe-rich hexagonal phase (H-phase, the crystal structure of which is still debatable). The PI's preliminary results show the surprising result that both ilmenite MgSiO3 and perovskite MgSiO3 are thermodynamically unstable at 30 GPa 0 Kelvin in the Mg-Si-O system, and no other ternary stable compounds exist at 30 GPa at all, which indicates a very important unexpected phenomenon can be observed and significant implications for enigmatic seismic features might be expected. Furthermore, besides the well-known seismic discontinuities at 410, 520, 660 km, another seismic discontinuity at 800 km is also seen in widely varying regions, but so far has no reasonable explanation, and another unknown phase might be expected. Minerals in the mantle are probably more complex than what we know currently. Theoretical simulations based on quantum mechanics have played an increasingly important role in Earth sciences. Therefore, the PI will apply the most advanced and recently developed tools in computational physics to address problems related to the mantle, core and core-mantle boundary region.
The PI will focus on three problems:
(1) Methodology development toward the prediction of materials with variable stoichiometry in ternary and even higher multi-component systems. The PI's recent work has shown that the prediction of binary systems based on the evolutionary approach is tractable. Since a number of important minerals in the context of earth sciences have puzzling stoichiometry, the remaining challenge is to predict stable ternary, quaternary and even higher multi-component systems at high P-T conditions.
(2) Prediction of Earth-forming minerals in the Mg-Fe-Ca-Al-Si-O and Fe-Si-C-S-H-O systems under given P-T conditions. Since the perovskite and post-perovskite phases in the real mantle have complex compositions, additional elements, like Ca, Al and C, can also affect the structure and stability field of phases. Therefore, crystal structure predictions for multicomponent systems will be addressed. Properties of Earth-forming minerals in the mantle and core will be computed. The nature of unexplained seismic discontinuities and H-phase are expected to be uncovered and some novel minerals are highly likely to be discovered in the mantle and core.
(3) Chemical reactions between the mantle and core. This study should greatly deepen our understanding of iron-based alloys, will lead to better understanding of chemistry and mineralogy of the Earth's core, as well as its peculiar properties (such as strong seismic anisotropy). Understanding of possible reactions at the core-mantle boundary region may shed light on some of the anomalous properties of that region.
In short, this project will look at materials of the most enigmatic regions of the Earth using advanced quantum-mechanical simulations. Central to this study is the PI's evolutionary algorithm USPEX, interfaced with first-principles electronic structure calculations. This approach has produced many important predictions in mineralogy and physics, successfully confirmed by subsequent experiments. |