Bukowinski This 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 and temperature 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.
