Computer Modelling of the Structure and Thermodynamic Properties of Silicate Minerals

One of the major aims of mineralogical research is to determine which minerals exist under given pressure, temperature and compositional conditions. This is of particular importance as mass transport deep in the Earth’s Mantle, and ultimately plate motion, will be governed by the behaviour of the component minerals. Hence a detailed understanding of their thermodynamic and kinetic properties under extreme pressures and temperatures will aid in our understanding of Mantle dynamics. Much of our current knowledge of the composition and properties of the Mantle comes from seismic studies, which show that the Earth has a layered structure. For example the Mantle is divided into three distinct layers, with the Upper Mantle comprising principally of olivine-structured magnesium silicate (forsterite), the Transition Zone of the same composition but comprised of minerals with the spinel structure, and finally another magnesium silicate mineral which is believed to have the perovskite structure forms the bulk of the Lower Mantle. These assignments are not unambiguous however but recent work using X-ray diffraction techniques with high pressure diamond anvil cells [1] is making progress in elucidating the crystal structure and relative stability of these phases under realistic conditions. As these experimental studies are often difficult, an attractive alternative is the use of computer simulation methods, which can now be used to model both the pressures and temperatures existing in the Mantle. Two recent developments in the field of atomistic simulation have made it possible to model silicate minerals under Mantle conditions.

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