Physics
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmmr43c1105d&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #MR43C-1105
Physics
3621 Mantle Processes (1038), 3924 High-Pressure Behavior, 5134 Thermal Properties, 8125 Evolution Of The Earth (0325), 8145 Physics Of Magma And Magma Bodies
Scientific paper
As the main medium for planetary differentiation, silicate liquids have a central role in the study of the chemical and dynamic evolution of planetary mantles and core formation. Central to our understanding of the properties of these liquids is the coupling between liquid structure and equilibrium thermodynamic properties as a function of pressure, temperature and composition. We perform first principles molecular dynamics simulations for liquid Mg2SiO4, in the framework of density functional theory and the local density approximation (LDA). Simulations are done in the canonical ensemble, and span a range of pressures (0 - 150 GPa) and temperatures (3000 - 6000 K) relevant to the deep earth. We find that on compression a decrease in the isochoric heat capacity together with an increase in the thermal pressure result in an increasing Grüneisen parameter, behavior opposite to that of most solids, but similar to that found in a recent first principles study of MgSiO3 liquid. Mean silicon coordination is found to increase linearly from four to six fold as a function of compression, with a variety of coordinated species present at all pressures. More detailed analysis of the liquid structure reveals increased polymerization at elevated temperatures, with free oxygens (not bound to Si) coexisting with semi-infinite silicate chains. The abundance of free oxygen decreases with compression, with chains transforming into more complex framework structures. A number of features in the pressure-temperature variation of the equation of state, diffusivity and electronic density of states of the liquid appear to be directly related to these changes in liquid structure.
de Koker N. P.
Karki Bijaya B.
Stixrude Lars
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