Dynamic Local Structure in Caesium Lead Iodide: Spatial Correlation and Transient Domains.

Area of Science:

• Materials Science
• Solid-State Physics
• Computational Chemistry

Background:

• Metal halide perovskites are semiconductors with tunable properties.
• These materials exhibit complex octahedral tilting and anharmonic atomic behavior.
• Understanding the atomistic dynamics in higher symmetry phases is crucial but lacking.

Purpose of the Study:

• Investigate the local structure and atomistic dynamics of inorganic perovskite CsPbI3.
• Elucidate the nature of dynamic structural features in higher symmetry phases.
• Provide a comprehensive picture of local structure and motion.

Main Methods:

• Utilized a novel machine learning force field based on the atomic cluster expansion framework.
• Performed large-scale simulations to analyze temporal and spatial correlations.
• Investigated octahedral tilt dynamics and local symmetry variations.

Main Results:

• Identified a double-well effective potential landscape for octahedral tilts, persisting into the cubic phase.
• Revealed dynamic, planar regions of lower symmetry within higher symmetry phases.
• Quantified the length and timescales of motion for these dynamic regions.

Conclusions:

• The local structure of CsPbI3 is highly dynamic, deviating from the average structure.
• Correlated octahedral motion leads to complex potential energy landscapes.
• These findings offer new insights into the behavior of metal halide perovskites.