Deep-Learning-Based Prediction of the Tetragonal → Cubic Transition in Davemaoite

Davemaoite, that is, CaSiO3 perovskite (CaPv), is the third most abundant phase in the lower mantle and exhibits a tetragonal-cubic phase transition at high pressures and temperatures. The phase boundary in CaPv has recently been proposed to be close to the cold slab adiabat and cause mid-mantle seismic wave speed anomalies (Thomson et al., 2019, ). This study utilized accurate deep-learning-based simulations and thermodynamic integration techniques to compute free energies at temperatures ranging from 300 to 3,000 K and pressures up to 130 GPa. Our results indicate that CaPv exhibits a single cubic phase throughout lower-mantle conditions. This suggests that the phase diagram proposed by Thomson et al. requires revision, and mid-mantle seismic anomalies are likely attributable to other mechanisms. Davemaoite, also known as calcium silicate perovskite (CaPv), is one of the most abundant minerals in Earth's lower mantle. It can exist in tetragonal and cubic crystal structures, depending on the pressure and temperature conditions. Determining the crystalline phase of CaPv is important for interpreting seismic observations of the lower mantle. A recent study (Thomson et al., 2019, ) suggested that CaPv's tetragonal-to-cubic transition could cause mid-mantle seismic anomalies. However, this phase transition has been a topic of debate. Previous studies have attempted to determine the phase boundary using ab initio methods. The computational cost and challenges associated with handling strong anharmonicity limited these approaches' accuracy and predictive power. In this study, we utilized deep learning and thermodynamic integration techniques to accurately compute the tetragonal to cubic phase boundary of CaPv across the lower mantle pressure range. Our results satisfactorily explain previous experimental measurements and support the notion that CaPv remains in the cubic phase across lower mantle conditions. These findings challenge the previously proposed phase diagram by Thomson et al. and suggest that mid-mantle seismic scatterers/reflectors or large low-shear-velocity provinces in the lower mantle cannot be attributed to this transition in CaPv. A deep-learning potential is developed to accurately determine CaSiO3 perovskite (CaPv)'s tetragonal-to-cubic phase boundary under lower-mantle conditions CaPv should exhibit solely a cubic phase throughout the entire lower mantle The tetragonal-to-cubic transition in CaPv is not a viable explanation for the mid-mantle seismic scatterers/reflectors or large low-shear-velocity provinces