Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
10121285 | Physics of the Earth and Planetary Interiors | 2005 | 11 Pages |
Abstract
We present ab initio calculations of the high-temperature axial c /a ratio of hexagonal-close-packed (hcp) iron at Earth's core pressures, in order to help interpret the observed seismic anisotropy of the inner core. The calculations are based on density functional theory, which is known to predict the properties of high-pressure iron with good accuracy. The temperature dependence of c /a is determined by minimising the Helmholtz free energy at fixed volume and temperature, with thermal contributions due to lattice vibrations calculated using harmonic theory. Anharmonic corrections to the harmonic predictions are estimated from calculations of the thermal average stress obtained from ab initio molecular dynamics simulations of hcp iron at the conditions of the inner core. We find a very gradual increase of axial ratio with temperature. This increase is much smaller than found in earlier calculations, but is in reasonable agreement with recent high-pressure, high-temperature diffraction measurements. This result casts doubt on an earlier interpretation of the seismic anisotropy of the inner core.
Related Topics
Physical Sciences and Engineering
Earth and Planetary Sciences
Geophysics
Authors
C.M. S. Gannarelli, D. Alfè, M.J. Gillan,