MgO at Multi-Megabar Pressures: Benchmarking the Equation of State and B1−B2 Transition Using Auxiliary-Field Quantum Monte Carlo

Studying materials at up to multi-megabar pressures is important for understanding the interiors of exoplanets and testing equation-of-state (EOS) models. However, it remains challenging to both experiments (e.g., B1–B2 transition pressure, P_tr, for MgO is uncertain by 130 GPa) and theory [two-parameter (zero-pressure bulk modulus K₀ and its pressure derivative K′₀) EOS is subject to >10% uncertainties for compression ratio >1.5, and prevalent density-functional-theory (DFT) computations can be biased by the exchange-correlation functional]. Advances in quantum Monte Carlo (QMC) have shown remarkable successes for solids. In this work, we develop and apply auxiliary-field (AF) QMC to benchmark the EOS and P_tr of MgO. In contrast to DFT predictions that vary by ~3% in equilibrium volume (V₀), ~6% in K₀ of B1 MgO, and ~30 GPa in P_tr, AFQMC can anchor all the three quantities with significantly reduced uncertainties, thereby providing an accurate and practical approach to benchmark materials properties at such extreme conditions.