Yang, Hua;
Wan, Lei;
Li, Yunguo;
Vočadlo, Lidunka;
Brodholt, John;
(2026)
Molecular-Dynamics Study of the Crystal Structure of Iron Under the Earth's Inner Core Conditions.
Journal of Geophysical Research: Solid Earth
, 131
(1)
, Article e2025JB032139. 10.1029/2025JB032139.
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Abstract
The crystal structure of Earth's solid inner core is fundamental to understanding the chemical composition and dynamical evolution of the core. However, despite extensive research, the structure still remains controversial with competing hypotheses regarding the stability of various Fe phases (e.g., bcc, fcc, and hcp). In this paper, we review the studies on the crystal structure of Fe under inner core conditions, and find, in line with previous work, that the main challenges come from the small energy differences between these structures. This has led to a variety of different conclusions across varying theoretical methods and precision, including ab initio, force field and machine learning methods. To address this problem, we employ a Bain path thermodynamic integration approach to reach consistent conclusions among different methods; we find that bcc Fe is mechanically stable but thermodynamically less stable under inner core conditions. Using the energetics from the Bain path method as a benchmark, we establish the requirements for converging free energy calculations through a two‐phase thermodynamic modeling approach. These calculations confirm that the hcp phase is the most stable, exhibiting the highest melting temperature regardless of the method used. This unified conclusion on the hcp phase as the stable crystal structure provides a robust foundation for future studies on Earth's core.
| Type: | Article |
|---|---|
| Title: | Molecular-Dynamics Study of the Crystal Structure of Iron Under the Earth's Inner Core Conditions |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1029/2025JB032139 |
| Publisher version: | https://doi.org/10.1029/2025jb032139 |
| Language: | English |
| Additional information: | This version is the author accepted manuscript. This version is the author accepted manuscript. It has been made open access under the Creative Commons (CC BY) licence under the terms of the UCL Intellectual Property (IP) Policy and UCL Publications Policy. |
| Keywords: | Earth's inner core, iron, crystal structure, free energy, atomistic simulation |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10220333 |
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