Elastic softening in the tetragonal-cubic transition in davemaoite

Davemaoite (Dm), or CaSiO₃ perovskite, poses challenges for experiments and simulations. This important phase in the Earth's lower mantle undergoes a cubic ↔ tetragonal phase transition due to pressure and temperature (P-T) changes. Until recently, there was no agreement on the transition boundary [1], which affects acoustic/seismic velocities. The high P-T conditions of this transition and the anharmonic nature of Dm have hindered detailed studies of this phenomenon. This work presents extensive molecular dynamics (MD) simulations of Dm's (ferro)elastic behavior across various P-T conditions. We use deep neural network potentials (DeepMD) trained on ab initio SCAN results to predict thermal equations of state, elastic properties under mantle conditions, and elastic anomalies near the cubic ↔ tetragonal boundary. Understanding the behavior of Dm at mantle conditions is the first step to understanding the seismological effects of the solid solution formation between bridgmanite (Bm) and Dm in the deep lower mantle.