Strong precursor softening in cubic CaSiO₃ perovskite.

Area of Science:

• Geophysics
• Mineral Physics
• Computational Materials Science

Background:

• Calcium silicate perovskite (CaSiO3) is a major lower mantle mineral with largely unresolved elastic properties.
• Understanding CaSiO3 elasticity is crucial for interpreting seismic data and modeling deep Earth processes.

Purpose of the Study:

• To investigate the elasticity of CaSiO3 perovskite across relevant lower mantle conditions.
• To determine the phase boundary and elastic behavior of CaSiO3 perovskite using advanced computational methods.

Main Methods:

• Ab initio machine-learning force fields (MLFF) were employed for molecular dynamics (MD) simulations.
• Simulations were conducted in the NVT ensemble to determine elastic properties and phase boundaries.
• Results were validated against experimental data at room temperature.

Main Results:

• MLFF-MD accurately reproduces experimental elastic properties of tetragonal CaSiO3 perovskite.
• The tetragonal-cubic phase boundary was established, confirming cubic CaSiO3 in the lower mantle.
• Cubic CaSiO3 exhibits anomalous precursor softening near the phase boundary, with implications for seismic observations.

Conclusions:

• The study validates MLFF-MD as a powerful tool for investigating deep Earth mineral elasticity.
• Anomalous softening of cubic CaSiO3 may explain seismically observed low-velocity zones, such as large low shear velocity provinces (LLSVPs).
• These findings offer insights into the composition and thermal state of the lower mantle and the origin of LLSVPs.