<i>Ab initio</i>equation of state of iron up to 1500 GPa

Bouchet, J.; Mazevet, S.; Morard, Guillaume; Guyot, F.; Musella, R.

doi:10.1103/physrevb.87.094102

Cited by 97 publications

(131 citation statements)

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“…Optical diagnostics coupled with hydrodynamic simulations give an associated temperature of 5680 K(± 700) suggesting that the melting curve of iron is below 5680 K at 260 GPa (upper limit of 5915 K deduced from the error bars). Once error bars are taken into account, the observation of solid or liquid iron along the Hugoniot using the XANES criterion is consistent with most existing data or models about iron melting [1,2,4,6,11,12] except for shock wave measurements based on self emission diagnostics [8][9][10], which gave a Hugoniot melting temperature of 6700 K at 260 GPa [8].…”

Section: Iron Phase Diagram and Discussionsupporting

confidence: 82%

“…In the continuation of the recent results available for iron [4], we thus generated a new EOS table based on ab initio molecular dynamics simulations. This table extends to the lower pressures and to the liquid phase, the tabulation of the ab initio simulation results published previously in Bouchet et al [2]. This EOS presents the advantage of a high pressure melting curve in agreement with the latest experimental data [4] that are in turn consistent with the ab initio results.…”

Section: Determination Of the Probed Thermodynamic Conditionssupporting

confidence: 82%

“…This suggests that the melting line of iron would have already been crossed at 260 GPa (± 29) -5680 K (± 700) along the principal Hugoniot of Fe. [4,6,38], shock-waves experiments [8][9][10][11][12][13], and ab-initio simulations [1][2][3]. The ICB pressure of 330 GPa is shown with a dashed blue line.…”

Section: Discussionmentioning

confidence: 99%

“…As a reference, the melting curve of pure iron, the main constituent of Earth's and Earth like planetary cores, is of a critical importance and has been the purpose of numerous experimental and theoretical works [1][2][3][4][5][6][7][8][9][10][11][12]. It remains up to now largely uncertain mainly due to experimental difficulties in reaching and detecting melting of iron at terrestrial Inner Core Boundary (ICB) conditions, where the pressure is of 330 GPa.…”

Section: Pacs Numbers: Valid Pacs Appear Herementioning

confidence: 99%

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X-ray absorption spectroscopy of iron at multimegabar pressures in laser shock experiments

Harmand¹,

Ravasio²,

Mazevet³

et al. 2015

Phys. Rev. B

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International audienceTaking advantage of the new opportunities provided by x-ray free electron laser (FEL) sources when coupled to a long laser pulse as available at the Linear Coherent Light Source (LCLS), we have performed x-ray absorption near-edge spectroscopy (XANES) of laser shock compressed iron up to 420 GPa (±50) and 10 800 K (±1390). Visible diagnostics coupled with hydrodynamic simulations were used to infer the thermodynamical conditions along the Hugoniot and the release adiabat. A modification of the pre-edge feature at 7.12 keV in the XANES spectra is observed above pressures of 260 GPa along the Hugoniot. Comparing with ab initio calculations and with previous laser-heated diamond cell data, we propose that such changes in the XANES pre-edge could be a signature of molten iron. This interpretation then suggests that iron is molten at pressures and temperatures higher than 260 GPa (±29) and 5680 K (±700) along the principal Fe Hugoniot

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Section: Iron Phase Diagram and Discussionsupporting

confidence: 82%

Section: Determination Of the Probed Thermodynamic Conditionssupporting

confidence: 82%

Section: Discussionmentioning

confidence: 99%

Section: Pacs Numbers: Valid Pacs Appear Herementioning

confidence: 99%

See 2 more Smart Citations

X-ray absorption spectroscopy of iron at multimegabar pressures in laser shock experiments

Harmand¹,

Ravasio²,

Mazevet³

et al. 2015

Phys. Rev. B

Self Cite

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show abstract

“…Hence, even more rigorous methods are needed to evaluate the FE of crystals as robustly as possible, if only to provide a basis for evaluating methods based on an effective harmonic model. Along these lines, AIMD calculations have been attempted for iron at extreme conditions [40][41][42][43][44][45] , but these efforts have had to use approximations of their own, in the DFT treatment and/or the FE computational method, trading off accuracy to gain useful precision in the result. Due to these challenges associated with ab initio-based approaches, classical force-fields and/or theories are often adopted to get an estimate of the FE.…”

Section: Introductionmentioning

confidence: 99%

Accurate and precise ab initio anharmonic free-energy calculations for metallic crystals: Application to hcp Fe at high temperature and pressure

et al. 2017

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A framework for computing the anharmonic free energy (FE) of metallic crystals using BornOppenheimer ab initio molecular dynamics (AIMD) simulation, with unprecedented efficiency, is introduced and demonstrated for the hcp phase of iron at extreme conditions (up to ≈ 290 GPa and 5000 K). The advances underlying this work are: (1) A recently introduced harmonically-mapped averaging temperature integration (HMA-TI) method reduces the computational cost by order(s) of magnitude compared to the conventional TI approach. The TI path starts from zero Kelvin, where it assumes the behavior is given exactly by a harmonic treatment; this feature restricts application to systems that have no imaginary phonons in this limit. (2) A Langevin thermostat with the HMA-TI method allows use of a relatively large MD time step (4 fs, which is about eight times larger than the size needed for the Andersen thermostat) without loss of accuracy. (3) AIMD sampling is accelerated by using density functional theory (DFT) with a low-level parameter set, then the measured quantities of selected configurations are robustly reweighted to a higher level of DFT. This introduces a speedup of about 20-30× compared to directly simulating the accurate system. (4a) The temperature (T ) dependence of the hcp equilibrium shape (i.e. c/a axial ratio) is determined (including anharmonicity), with uncertainty less than ±0.001. (4b) Electronic excitation is included through Mermin's finite-temperature extension of the T = 0 K DFT. A simple FE perturbation method is introduced to handle the difficulty associated with applying the TI method with a Tdependent geometry and (due to electronic excitation) potential-energy surface. (5) The FE in the thermodynamic limit is attained through extrapolation of only the (computationally inexpensive) quasiharmonic FE, because the anharmonic FE contribution has negligible finite-size effects. All methods introduced here do not affect the AIMD sampling -results are obtained through postprocessing -so established AIMD codes can be employed without modification. Analytical formulas fitted to the results for the variation of the equilibrium c/a ratio and FE components with T are provided. Notably, effects of magnetic excitations are not included, and may yet prove important to the overall FE; if so, it is plausible that such contributions can be added perturbatively to the FE values reported here. Notwithstanding these considerations, FE values are obtained with an estimated accuracy and precision of 2 meV/atom, suggesting that the capability to compute the phase diagram of iron at Earth's inner core conditions is within reach.

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Is inner core seismic anisotropy a marker for plastic flow of cubic iron?

Lincot

Merkel

Cardin

2015

Geophysical Research Letters

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International audienceThis paper investigates whether observations of seismic anisotropy are compatible with a cubic structure of the inner core Fe alloy.We assume that anisotropy is the result of plastic deformation within a large scale flow induced by preferred growth at the inner core equator. Based on elastic moduli from the literature, bcc- or fcc-Fe produce seismic anisotropy well below seismic observations ($<0.4\%$). A Monte-Carlo approach allows us to generalize this result to any form of elastic anisotropy in a cubic system. Within our model, inner core global anisotropy is not compatible with a cubic structure of Fe alloy.Hence, if the inner core material is indeed cubic, large scale coherent anisotropic structures, incompatible with plastic deformation induced by large scale flow, must be present

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Ab initioequation of state of iron up to 1500 GPa

Cited by 97 publications

References 59 publications

X-ray absorption spectroscopy of iron at multimegabar pressures in laser shock experiments

X-ray absorption spectroscopy of iron at multimegabar pressures in laser shock experiments

Accurate and precise ab initio anharmonic free-energy calculations for metallic crystals: Application to hcp Fe at high temperature and pressure

Is inner core seismic anisotropy a marker for plastic flow of cubic iron?

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