Modeling defects and plasticity in MgSiO₃ post-perovskite: Part 1-generalized stacking faults

Area of Science:

• Geophysics and Planetary Science
• Materials Science
• Computational Mineral Physics

Background:

• MgSiO3 post-perovskite is a key mineral in Earth's D″ layer, influencing deep mantle geodynamics.
• Understanding dislocation mobility and fault energies in this phase is critical for interpreting seismic data and mantle convection.
• Previous studies often relied on computationally expensive ab initio methods.

Purpose of the Study:

• To assess the transferability of a pairwise potential model, originally developed for MgSiO3 perovskite, to MgSiO3 post-perovskite.
• To accurately compute the excess energies of generalized stacking faults (GSF, or γ-surfaces) in MgSiO3 post-perovskite at 120 GPa.
• To identify favorable slip systems for dislocation glide in MgSiO3 post-perovskite under deep mantle conditions.

Main Methods:

• Utilized a transferable pairwise potential model derived for MgSiO3 perovskite.
• Performed generalized stacking fault energy (γ-surface) calculations for MgSiO3 post-perovskite at 120 GPa.
• Systematically analyzed all potential slip plane locations within the post-perovskite crystal structure.

Main Results:

• The pairwise potential model successfully computed GSF energies in MgSiO3 post-perovskite.
• Calculations identified slip systems with the smallest shear vector [100] and the [001](010) system as having the easiest glide.
• Results align with previous ab initio calculations, confirming the model's accuracy.

Conclusions:

• The chosen pairwise potential model is validated for atomistic simulations of MgSiO3 post-perovskite.
• This model provides a computationally efficient alternative for studying dislocations and plastic deformation in the deep mantle.
• Findings support further full atomistic modeling of dislocations in MgSiO3 post-perovskite for enhanced geodynamic insights.