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Thermodynamics of hexagonalclosepacked iron under Earth's core conditions

Summary: Thermodynamics of hexagonal­close­packed iron
under Earth's core conditions
D. Alf`e 1 , G. D. Price 1 and M. J. Gillan 2
1 Research School of Geological and Geophysical Sciences
Birkbeck and University College London
Gower Street, London WC1E 6BT, UK
2 Physics and Astronomy Department, University College London
Gower Street, London WC1E 6BT, UK
The free energy and other thermodynamic properties of hexagonal­close­packed iron are calcu­
lated by direct ab initio methods over a wide range of pressures and temperatures relevant to the
Earth's core. The ab initio calculations are based on density­functional theory in the generalised­
gradient approximation, and are performed using the projector augmented wave (PAW) approach.
Thermal excitation of electrons is fully included. The Helmholtz free energy consists of three parts,
associated with the rigid perfect lattice, harmonic lattice vibrations, and anharmonic contributions,
and the technical problems of calculating these parts to high precision are investigated. The har­
monic part is obtained by computing the phonon frequencies over the entire Brillouin zone, and
by summation of the free­energy contributions associated with the phonon modes. The anhar­
monic part is computed by the technique of thermodynamic integration using carefully designed
reference systems. Detailed results are presented for the pressure, specific heat, bulk modulus, ex­
pansion coefficient and Gr¨uneisen parameter, and comparisons are made with values obtained from


Source: Alfè, Dario - Departments of Earth Sciences & Physics and Astronomy, University College London


Collections: Physics; Geosciences