Structural evolution of the Fe-Si binary system under extreme pressure

The stability of Fe-Si compounds under extreme pressure is critical for understanding the composition and evolution of Earth's core and terrestrial planetary interiors. Using first-principles calculations and adaptive genetic algorithm crystal structure prediction method, we systematically investigated the thermodynamic stability of Fe-Si compounds and their structural evolution as a function of silicon concentration over pressures ranging from 0 GPa to 1 TPa. At 0 K, B2-FeSi is identified as the sole thermodynamically stable phase at high pressures. Through structural characterization analysis of metastable structures, we found that as the Si content increases, there is a transition in structural motifs from hcp to bcc and then to fcc. Furthermore, electronic and vibrational entropies significantly enhance the thermodynamic stability of certain alloy structures. Our study highlights the synergistic effects of composition, pressure, and volume in regulating phase stability, providing theoretical insights into the composition and structural evolution of planetary cores.