Ab Initio Electron-Gas Models With Polarizable Ions: Applications to Complex Minerals in the Transition Zone and Lower Mantle

9814304 Bukowinski这是一个项目的继续，该项目使用密度泛函理论来开发自洽的从头计算模型，以及有效的伪经验模型，研究可变形离子对压力和温度引起的晶体环境变化的响应。这些模型旨在通过提供准确而又非常有效的技术来模拟石榴石等复杂矿物，从而补充第一性原理方法，这些复杂矿物仍然超出了完全第一性原理方法的实际范围。将包括球形和非球形变形，以及长程范德华相互作用的影响。作为特例，该模型将包括当前的电子气势理论。这些模型将被用来检验过渡带和由SiO、MgO、FeO、CaO和Al_2O_3组成的下地幔矿物的静态和动态性质。蒙特卡罗、分子动力学和模拟退火技术将用于探索在中压和极高压力和温度下可能形成的矿物结构，以及压力对含有硅酸盐成分的熔体结构的影响。同样的方法将被用来估计建模矿物组合所需的热参数，这些矿物组合可能解释观测到的地幔的地震性质。新的模型还应该能够检查离子极化率的压力依赖性，以及晶体的极化率和极化率对扩散、元素分配以及红外和拉曼幅度的影响。如果成功，新模型将提供各种类型的实验数据之间的联系，以及在极端温度和压力条件下的矿物和流体模型。扩大的认识和新的理论工具应有助于更好地了解地幔中地震速度的径向不连续性、各向异性和横向不均匀的可能来源，以及对地震速度和地球地球化学演化的热、结构和化学效应。该项目由岩石学、地球化学和地球物理项目共同资助。

9814304BukowinskiThis is a continuation of a project that uses density functional theory to develop self-consistent ab initio models, as well as efficient pseudoempirical models, of the response of deformable ions to pressure andtemperature induced changes in crystal environments. These models are designed to complement first principles methods by providing accurate and yet very efficient techniques capable of simulating complex minerals like garnets that remain beyond the practical reach of fully first principles methods. Spherical and non-spherical deformations will be included, as well as the effects of long-ranged van der Waals interactions. The model will include, as special cases, current electron-gas potential theories. The fully developed models will then be used to examine the static and dynamic properties of transition zone and lower mantle minerals composed of SiO2, MgO, FeO, CaO and Al2O3. Monte Carlo, molecular dynamics and simulated annealing techniques, will be used to explore mineral structures that may form at ntermediate and very high pressures and temperatures, as well as the effects of pressure on the structure of melts with silicate compositions. The same methods will be used to estimate thermal parameters needed to model mineral assemblages that may account for the observed seismic properties of the mantle. The new models should also allow examination of the pressure dependence of ionic polarizabilities, as well as crystal polarizabilities and the effects of polarizability on diffusion, element partitioning and IR and Raman amplitudes. If successful, the new models stand to provide a link among various types of experimental data and models of minerals and fluids at extreme conditions of temperature and pressure. The expanded understanding and new theoretical tools should lead to a better understanding of possible sources of radial discontinuities, anisotropy and lateral heterogeneity of seismic velocities in the mantle of the Earth, and of thermal, structural and chemical effects on seismic velocities and the geochemical evolution of the earth. This project is jointly funded by the Petrology & Geochemistry and Geophysics Programs.