dorsal/arxiv
View SchemaThe axial ratio of hcp iron at the conditions of the Earth's inner core
| Authors | C. M. S. Gannarelli, D. Alfe, M. J. Gillian |
|---|---|
| Categories | |
| ArXiv ID | physics/0409109 |
| URL | https://arxiv.org/abs/physics/0409109 |
| DOI | 10.1016/j.pepi.2005.06.003 |
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.
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"abstract": "We present ab initio calculations of the high-temperature axial c/a ratio of\nhexagonal-close-packed (hcp) iron at Earth\u0027s core pressures, in order to help\ninterpret the observed seismic anisotropy of the inner core. The calculations\nare based on density functional theory, which is known to predict the\nproperties of high-pressure iron with good accuracy. The temperature dependence\nof c/a is determined by minimising the Helmholtz free energy at fixed volume\nand temperature, with thermal contributions due to lattice vibrations\ncalculated using harmonic theory. Anharmonic corrections to the harmonic\npredictions are estimated from calculations of the thermal average stress\nobtained from ab initio molecular dynamics simulations of hcp iron at the\nconditions of the inner core. We find a very gradual increase of axial ratio\nwith temperature. This increase is much smaller than found in earlier\ncalculations, but is in reasonable agreement with recent high-pressure,\nhigh-temperature diffraction measurements. This result casts doubt on an\nearlier interpretation of the seismic anisotropy of the inner core.",
"arxiv_id": "physics/0409109",
"authors": [
"C. M. S. Gannarelli",
"D. Alfe",
"M. J. Gillian"
],
"categories": [
"physics.geo-ph"
],
"doi": "10.1016/j.pepi.2005.06.003",
"title": "The axial ratio of hcp iron at the conditions of the Earth\u0027s inner core",
"url": "https://arxiv.org/abs/physics/0409109"
},
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