PBE-GGA predicts the B8↔B2 phase boundary of FeO at Earth’s core conditions

Journal Article · Mon Jul 03 00:00:00 EDT 2023 · Proceedings of the National Academy of Sciences of the United States of America

DOI:https://doi.org/10.1073/pnas.2304726120· OSTI ID:1987984

Zhang, Zhen ^[1]; Sun, Yang  ^[2]; Wentzcovitch, Renata M.  ^[3]

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1. Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY 10027
2. Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY 10027, Department of Physics, Iowa State University, Ames, IA 50011
3. Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY 10027, Department of Earth and Environmental Sciences, Columbia University, New York, NY 10027, Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964, Data Science Institute, Columbia University, New York, NY 10027

FeO is a crucial component of the Earth’s core, and its thermodynamic properties are essential to developing more accurate core models. It is also a notorious correlated insulator in the NaCl-type (B1) phase at ambient conditions. It undergoes two polymorphic transitions at 300 K before it becomes metallic in the NiAs-type (B8) structure at ~100 GPa. Although its phase diagram is not fully mapped, it is well established that the B8 phase transforms to the CsCl-type (B2) phase at core pressures and temperatures. Here, we report a successful ab initio calculation of the B8↔B2 phase boundary in FeO at Earth’s core pressures. We show that fully anharmonic free energies computed with the Perdew–Burke–Ernzerhof-generalized gradient approximation coupled with thermal electronic excitations reproduce the experimental phase boundary within uncertainties at P > 255 GPa, including the largely negative Clapeyron slope of –52 MPa/K. This study validates the applicability of a standard density functional theory functional to FeO under Earth’s core conditions and demonstrates the theoretical framework that enables complex predictive studies of this region.

• Sponsoring Organization: USDOE
• Grant/Contract Number: SC0019759
• OSTI ID: 1987984
• Journal Information: Proceedings of the National Academy of Sciences of the United States of America, Journal Name: Proceedings of the National Academy of Sciences of the United States of America Vol. 120 Journal Issue: 28; ISSN 0027-8424
• Publisher: Proceedings of the National Academy of Sciences
• Country of Publication: United States
• Language: English