Iron under Earth’s core conditions: Liquid-state thermodynamics and high-pressure melting curve from ab initio calculations

By Dario Alfè, G. D. Price, Michael J. Gillan. 2001

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Ab initio techniques based on density functional theory in the projector-augmented-wave implementation are used to calculate the free energy and a range of other thermodynamic properties of liquid iron at high pressures and temperatures relevant to the Earth’s core. The ab initio free energy is obtained by using thermodynamic integration to calculate the change of free energy on going from a simple reference system to the ab initio system, with thermal averages computed by ab initio molecular dynamics simulation. The reference system consists of the inverse-power pair-potential model used in previous work. The liquid-state free energy is combined with the free energy of hexagonal close packed Fe calculated earlier using identical ab initio techniques to obtain the melting curve and volume and entropy of melting. Comparisons of the calculated melting properties with experimental measurement and with other recent ab initio predictions are presented. Experiment-theory comparisons are also presented for the pressures at which the solid and liquid Hugoniot curves cross the melting line, and the sound speed and Gruneisen parameter along the Hugoniot. Additional comparisons are made with a commonly used equation of state for high-pressure–high-temperature Fe based on experimental data.

Subfields: Geophysics, Materials Chemistry

View Paper: https://www.semanticscholar.org/paper/b63d79cb9ef50d19b56d33a5c77455bab40a4e03

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Citations in the corpus

Tomographic filtering of high‐resolution mantle circulation models: Can seismic heterogeneity be explained by temperature alone? (2009, result): “We note that a high CMB temperature and a correspondingly large temperature drop across D′′, with associated high heat flow, is consistent with a number of studies from geodynamics, seismology and mineral physics [e.g., Glatzmaier and Roberts , 1995; Kuang and Bloxham, 1997; Boehler , 2000; Steinle-”
Energetics of the Core (2015, background): “Thermodynamic arguments (e.g. Anderson 1998) and molecular dynamics simulations (e.g. Alfe et al. 2002b) both suggest that the value of Gruneisen’s parameter γ is close to a constant value of 1.5 throughout the core.”
Stratification of the top of the core due to chemical interactions with the mantle (2010, background): “The volume of the solid mixture is increased by 2% to account for the volume change on melting, based on estimates for pure iron [ Alfè et al. , 2002].”
The properties of iron under core conditions from first principles calculations (2003, methodology): “(2000)and byBelonosko et al. (2000)to study the melting of Fe.”
Phase relations in the Fe-FeSi system at high pressures and temperatures (2013, background): “…51 et al., 2010), to ~6-7 wt% (Allègre et al., 1995, Brosh et al., 2009; Javoy et al., 2010; McDonough, 52 2003; Shahar et al., 2009), to 8-12 wt% (Alfè et al., 2002; Asanuma et al., 2011; Fischer et al., 53 2012; Lin et al., 2003; Ricolleau et al., 2011; Rubie et al., 2011), to up to 20 wt%…”
Thermal versus elastic heterogeneity in high‐resolution mantle circulation models with pyrolite composition: High plume excess temperatures in the lowermost mantle (2009, background): “When combined with seismic constraints the material simulations place estimates of the innercore boundary (ICB) temperature at 5400–5700 K [Steinle-Neumann et al., 2001; Alfè et al., 2002].”
The influence of potassium on core and geodynamo evolution (2003, background): “The melting temperature for pure iron at ICB pressures (330 GPa) is 6300 ± 300 K, including a free-energy correction, and the gradient at 350 GPa is 9 K GPa−1 ( Alfe et al. 2002a ).”
HOW THERMAL EVOLUTION AND MASS-LOSS SCULPT POPULATIONS OF SUPER-EARTHS AND SUB-NEPTUNES: APPLICATION TO THE KEPLER-11 SYSTEM AND BEYOND (2012, background): “We assume a core heat capacity of cv = 0.5–1.0 J K−1 g−1 (Alfè et al. 2002; Guillot et al. 1995; Valencia et al. 2010) as in Nettelmann et al. (2011).”
Thermal and electrical conductivity of solid iron and iron-silicon mixtures at Earth's core conditions (2013, methodology): “In order to decide how to distribute the silicon atoms in the solid mixtures, we used the results obtained in Alfè et al. (2002).”
Can the Earth's dynamo run on heat alone? (2003, unknown): “The remaining quantities have so far come from high-pressure experiments on iron and extrapolations of known properties to high pressures and temperatures (Anderson & Ahrens 1994).”
Thermal and magnetic evolution of the Earth’s core (2003, methodology): “(3) Tad(r, t) = Ts [c(t)] exp [ − ∫ r c(t) αg CP dr′ ] , (9) where the boundary condition that the temperature at the ICB (r = c(t)) is equal to the temperature of crystallization at this placeTs[c(t)] has been used.”