Elasticity and acoustic velocities of δ-AlOOH at geophysical conditions*

δ-AlOOH is a prototypical high-pressure hydrous phase for understanding deep water storage and circulation in Earth's deep interior. However, its elasticity and acoustic velocities remain undetermined at high pressures and temperatures. This study evaluates the adiabatic elastic tensor and acoustic velocities of δ-AlOOH at mantle pressures and temperatures. The elastic tensor is computed using molecular dynamics with a machine-learning force field constructed based on the SCAN meta-GGA description of the system. This method enables us to tackle the long-standing issue of anharmonicity across the pressure-induced H-bond symmetrization and reach extreme temperatures up to δ's superionic regime. Our ambient condition results are in excellent agreement with recent single-crystal measurements, showcasing the validity and effectiveness of our approach.