Abstract

The authors present a detailed theoretical study of the melting curve of iron from normal conditions up to pressures of 1.5 Mbar, i.e. up to pressures characteristic for the boundary between the Earth's mantle and its core. The analysis is based on simple effective interatomic pair interactions derived from a combined nearly free-electron treatment of the s electrons and a tight-binding treatment of the d electrons. The free energies of the solid and liquid phase are calculated using thermodynamic variational methods. For the solid they use an Einstein reference system. For the liquid both hard-sphere and soft-sphere variational systems are investigated. The soft-sphere reference system produces a lower (and hence more accurate) liquid free energy. This is necessary to achieve a quantitative description of the melting properties. In particular, the predicted increase of the melting temperature with pressure is in reasonable agreement with recent measurements reported by Q. Williams and co-workers (1987).

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