COLLABORATIVE RESEARCH: Theoretical Investigation of Core Materials

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Stixrude 9980553 Cohen 9980602 The investigators propose to obtain a better understanding of the structure, evolution and processes of the Earth's core through computations of the atomic-scale physics of iron and iron alloys. In this renewal, they will build on the achievements of prior research by applying fast and efficient methods, developed during earlier grant periods, to problems important to high-pressure geophysics, in particular to the computation of accurate high temperature properties. A variety of electronic structure methods that are more efficient than the all electron linearized-augmented-plane-wave (LAPW) method will be used in high temperature calculations, including a projector mixed-basis method and a total energy tight-binding model. Statistical mechanical methods will include: 1) The particle in a cell model, which permits rapid calculation of equilibrium thermodynamic properties including anharmonic terms, and 2) Ab initio molecular dynamics which allows calculations of equilibrium properties, as well as transport and defect properties. The treatment of magnetism at high temperature will receive special attention because this is important in the relatively low-pressure regime (1 Mbar) where most experimental data exist. The investigators will investigate a number of areas that are important to our understanding of the earth's inner and outer core including: 1) the sub-solidus phase diagram of iron; 2) the elasticity of solid iron at high temperature and high pressure; 3) the formation of vacancies and diffusion in solid iron at low and high pressures; 4) extended defects and rheology; 5) the melting curve of iron; 6) the equilibrium and transport properties of liquid iron including anelastic properties; and 7) the effect of alloying elements (including Ni, O, S, C and H) on the physics of liquid and solid iron.