DYNAMICS OF MINERALS - IMPLICATIONS FOR THE STUDIES OF THE EARTHS INTERIOR

One of the major goals of geophysics is to predict the thermodynamic p roperties and phase transitions of minerals at high pressure and tempe rature. A key requirement of predicting the thermodynamic properties o f solids is an accurate description of its density of states. In this paper, we review our ongoing program aimed at providing a microscopic understanding of the vibrational adn thermodynamic properties of silic ate minerals. Lattice dynamical model calculations backed by Raman sca ttering an inelastic neutron scattering studies have been undertaken t o study the phonon dispersion relations, density of states and thermod ynamic properties of several minerals. The calculations enabled a micr oscopic interpretation of the experimental data and have been successf ul in predicting the variations in the vibrational spectra in the vari ous mineral phases of the Earth's mantle. The computed macroscopic the rmodynamic properties and phase diagram of these minerals are in good agreement with experimental data. Molecular dynamics simulations of ph ase transitions of the MgSiO3 polymorphs have enabled an understanding of the relative stability and phase diagram of these minerals at pres sures and temperatures characteristic of the Earth's interior.