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Thermodynamics of hexagonal-close-packed iron under Earth's core conditions D. Alfe`,1,2
 

Summary: Thermodynamics of hexagonal-close-packed iron under Earth's core conditions
D. Alfe`,1,2
G. D. Price,1
and M. J. Gillan2
1
Research School of Geological and Geophysical Sciences, Birkbeck and University College London, Gower Street,
London WC1E 6BT, United Kingdom
2
Physics and Astronomy Department, University College London, Gower Street, London WC1E 6BT, United Kingdom
Received 26 August 1999; revised manuscript received 7 December 2000; published 9 July 2001
The free energy and other thermodynamic properties of hexagonal-close-packed iron are calculated 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 density-functional theory in the generalized-gradient approximation, and are per-
formed using the projector augmented wave approach. Thermal excitation of electrons is fully included. The
Helmholtz free energy consists of three parts, associated with the rigid perfect lattice, harmonic lattice vibra-
tions, and anharmonic contributions, and the technical problems of calculating these parts to high precision are
investigated. The harmonic part is obtained by computing the phonon frequencies over the entire Brillouin
zone, and by summation of the free-energy contributions associated with the phonon modes. The anharmonic
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, expansion coefficient and Gru¨n-

  

Source: Alfè, Dario - Departments of Earth Sciences & Physics and Astronomy, University College London
Price, G. David - Department Earth Sciences, University College London

 

Collections: Geosciences; Materials Science; Physics