Insights Into the Core’s Structure, Formation and Evolution from First-Principles Calculations

Citation

Liu, Weiyi (2025) Insights Into the Core’s Structure, Formation and Evolution from First-Principles Calculations. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/ps54-bx05. https://resolver.caltech.edu/CaltechTHESIS:06022025-184329081

Abstract

Understanding the formation, composition, and evolution of planetary cores is essential to unraveling the early history and internal dynamics of terrestrial planets. However, direct constraints on the physical and chemical properties of liquid metal under core-forming conditions remain limited due to the inaccessibility of the core and the challenges of reproducing its extreme pressures and temperatures in the laboratory. This thesis integrates first-principles molecular dynamics(FPMD)simulations with high-pressure experimental data to investigate the thermodynamics, chemical partitioning, and seismic implications of multicomponent metal liquids in the deep interiors of Earth and other differentiated bodies.

This thesis focuses on two fundamental properties of the core: its thermodynamic behavior and its chemical interaction with the silicate mantle during differentiation. The first part of the thesis develops a thermodynamic model for multicomponent metallic liquids—including Fe–Ni systems with light elements such as O, S, Si, C, and H–based on FPMD simulations and calibrated against experimental data. This model accurately reproduces pressure–volume–temperature relations and mixing behavior, and is consistent with both diamond anvil cell and shock wave measurements. The model forms the basis for a forward seismic modeling framework that allows direct comparison between core composition and observed density and velocity profiles in Earth’s outer core. The second part of the thesis investigates the chemical partitioning of elements that record early planetary formation and evolution—specifically Sm, Nd, I, and Pu—between metal and silicate liquids at high temperatures. Two different approaches are employed to determine the partition coefficients: thermodynamic integration based on first-principles molecular dynamics for Sm and Nd, and two-phase FPMD simulations for I and Pu. With these partitioning behaviors quantified, the study further models core formation processes in differentiated planetesimals and Earth, providing new constraints on the extent of metal–silicate chemical exchange and fresh insights into the isotopic and volatile evolution of planetary mantles.

Thesis Files