Ab initio simulations on metal-silicate partitioning of phosphorus during Earth’s core formation

Phosphorus (P) partitioning between metal and silicate is a key indicator for understanding Earth’s differentiation and accretion processes. However, the complexity of phosphorus valence states in experiments, combined with limited temperature and pressure conditions, introduces significant uncertainties regarding its partitioning behavior under high-pressure conditions. Here, we use ab initio molecular dynamics simulations to investigate the partitioning of P in three valence states (pentavalent(+5), divalent(+2), and zero-valent(0)) at 10–135 GPa and 3000–5000 K. We find that the partition coefficients of phosphorus in these valence states generally increase with pressure. Specifically, the partition coefficient of zero-valent P ranges from 1.33 ± 1.72 to 5.7 ± 1.13, while divalent P ranges from 1.54 ± 1.85 to 6.63 ± 1.43 and pentavalent P ranges from 2.81 ± 1.58 to 10.78 ± 1.54. These high partition coefficients impose significant constraints on Earth’s accretion processes. Considering plausible scenarios for Earth’s core formation, our results suggest that a single-stage model cannot fully account for the P budget in the mantle. Instead, only a multi‐stage core formation model is feasible, with disequilibrium during the final impacts playing a crucial role. The degree of disequilibrium depends on the extent of differentiation of the final impactors. If early impactors were already differentiated, at least two complete disequilibrium events would be required. However, if the impactors remained undifferentiated, only the final impactor-likely a carbonaceous chondrite (CC) embryo comprising about 6 % of Earth’s mass—would suffice.