Structures of Liquid Iron–Light‐Element Mixtures under High Pressure

Abstract

The effects of light elements such as H, C, O, Si, and S on the local structures of liquid Fe under high pressure are investigated by ab initio molecular dynamics (MD) simulations. The simulations clarify that H, C, and O are incorporated into liquid Fe interstitially while Si and S are “substitutional” type impurities. From the calculated partial pair distribution functions, it is found that an interaction between light elements exists even under high‐pressure conditions exceeding 100 GPa. Additionally, the interaction depends on the type of element. The CC interactions are stronger than those of other light elements. The SS interactions depend on the S concentration, in the sense that the shape of pair distribution functions for the SS correlation changes with increasing S concentration.

Iron‐Carbon Alloy Under Shock Compression: Implications for the Carbon Concentration in Earth’s Inner Core

“…Recent ab initio molecular dynamics (AIMD) simulations show that carbon could also take the interstitial form in liquid iron at the relevant outer‐core conditions (e.g., 140 GPa and 5,000 K; Ohmura et al., 2020). In this case, the effect of interstitial carbon on the density of liquid iron could be the same as that in solid iron.…”

Ab Initio Molecular–Dynamics Study of Structural and Bonding Properties of Liquid Fe–Light–Element–O Systems Under High Pressure

“…The cutoff energies of the plane wave were 30 and 300 Ry for the pseudo-wavefunctions and pseudo-charge density, respectively. These cutoff energies were the same as those used in a previous study (Ohmura et al, 2020). The energy functional was minimized using an iterative scheme based on the preconditioned conjugate-gradient method (Kresse and Hafner, 1994;Shimojo et al, 2001).…”

“…More recently, a systematic theoretical investigation based on ab initio MD simulations for the LE-effect on the structural properties of liquid Fe-LE binary systems under high pressure was reported (Ohmura et al, 2020). The simulation clarified that H, C, and O are incorporated into liquid Fe interstitially, while Si and S are "substitutional" type impurities.…”

“…Recently, Morard et al clarified the compression mechanism of liquid Fe-C from X-ray diffraction measurements and demonstrated that the compression rate for the first coordination shell was higher than that for the second and third (Morard et al, 2017). Theoretically, the structures of liquid Fe-H, Fe-C, Fe-N, Fe-O, Fe-Mg, Fe-Si, and Fe-S under high pressure were investigated using ab initio molecular dynamics (MD) simulations (Alfe and Gillan, 1998;Alfe et al, 1999;Morard et al, 2014;Ichikawa and Tsuchiya, 2015;Posner and Steinle-Neumann, 2019;Ohmura et al, 2020). Alfe et al investigated the structure of liquid Fe-S at 330 GPa and 6000 K and suggested that there was no tendency for S atoms to form chains (Alfe and Gillan, 1998).…”

Experimental determination of carbon diffusion in liquid iron at high pressure

“…For isobaric fits, the numerator in the exponent is replaced by an enthalpy ΔH* (e.g., Ni et al, 2015) and the pre-exponential factor is labeled as 0 * in these cases. Carbon is incorporated interstitially into both solid (e.g., Goldschmidt, 1967) and liquid iron (e.g., Sobolev and Mirzoev, 2013;Ohmura et al, 2020) and is therefore expected to show relatively similar diffusion behavior to other interstitial elements (e.g., O and N) as predicted by density-functional molecular dynamics (DFT-MD) simulations (e.g., Posner and Steinle-Neumann, 2019).…”