The Equations of State of Liquid Pure Fe and Fe-light Elements Alloys by Ab Initio Molecular Dynamics Simulations

Abstract:

The equation of state (EoS) of pure Fe and Fe-light elements alloy liquids were calculated by means of ab initio molecular dynamics simulations at the outer core P-T conditions. In the outer core, many light elements, such as carbon, nitrogen, oxygen, hydrogen, sulfur, and silicon, have been proposed as possible constituents. The concentrations of these elements have been strongly debated for years. In this study, the complete EoS models of liquid iron alloys were determined from ab initio molecular dynamics computations in a wide range of pressure, temperature, and compositional space. Then, internally consistent thermodynamic and elastic properties of pure Fe and Fe-light elements alloys, in particular density, adiabatic bulk modulus, and P-wave velocity were analyzed in order to clarify the effect of light elements incorporation on seismically observable data. We examined the Fe-Ni-O-Si-S-C system and confined the likely composition range in the outer core. A substantial variation of thermal conductivity can be seen even in the obtained composition range.