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Summary: Thermodynamics from first principles:
temperature and composition of the Earths core
D. ALFE`1,2,
*, M. J. GILLAN
1
AND G. D. PRICE
2
1
Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
2
Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, UK
ABSTRACT
We summarize the main ideas used to determine the thermodynamic properties of pure systems and
binary alloys from first principles calculations. These are based on the ab initio calculations of free
energies. As an application we present the study of iron and iron alloys under Earth's core conditions.
In particular, we report the whole melting curve of iron under these conditions, and we put constraints
on the composition of the core. We found that iron melts at 6350±600 K at the pressure corresponding
to the boundary between the solid inner core and the liquid outer core (ICB). We show that the core
could not have been formed from a binary mixture of Fe with S, Si or O and we propose a ternary or
quaternary mixture with 810% of S/Si in both liquid and solid and an additional ~8% of oxygen in
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