Investigating the impact of temperature on hydrous magnesium silicate Phase D using deep-learning-driven interatomic potentials

The study of hydrogen bonding symmetry in lower mantle water-bearing minerals is scientifically critical for understanding the water cycle in the deep Earth, the stability and physical properties of minerals, and the electrical conductivity structure of the Earth's interior. We report classical molecular dynamics simulations of Phase D $({\mathrm{MgSi}}_{2}{\mathrm{O}}_{6}{\mathrm{H}}_{2})$, a dense hydrous magnesium silicate, using a deep-learning-optimized interatomic potential, demonstrating spontaneous hydrogen bonding symmetrization emergence at 33.7 GPa under hydrostatic compression. Additionally, within a specific pressure-temperature range, we observed abnormal phenomena in bulk modulus and lattice constant ratio. Further analysis indicates that these anomalies are actually caused by the phase transition from asymmetric hydrogen-bonded state 1 (AHB1) to AHB2 and the proton-disordering transition, decoupled from hydrogen bonding symmetry. This study provides insight into the structure and dynamics of the Earth's interior, as well as the distribution and occurrence state of hydrogen within the Earth.