Precessional Dynamics of Octahedra in CsPbBr₃

Area of Science:

• Materials Science
• Solid-State Physics
• Computational Chemistry

Background:

• ABX3 halide perovskites feature corner-sharing BX6 octahedra crucial for their phases.
• These materials exhibit significant octahedral dynamics due to their soft mechanical nature and shallow energy landscape.
• Understanding these dynamics is key to their structural transitions and physical properties, but experimental and computational methods face limitations.

Purpose of the Study:

• To develop a machine-learning potential for accurate, large-scale molecular dynamics simulations of halide perovskites.
• To investigate the rotational dynamics of individual octahedra in CsPbBr3.
• To elucidate the dominant mechanisms of octahedral motion and challenge existing models.

Main Methods:

• Development of a novel machine-learning potential for simulating perovskite structures.
• Execution of large-scale molecular dynamics simulations with near-density functional theory (DFT) accuracy.
• Analysis of the temporal evolution and rotational behavior of individual BX6 octahedra in CsPbBr3.

Main Results:

• The study successfully simulated large-scale molecular dynamics of CsPbBr3 with high accuracy.
• Contrary to common assumptions, the typical a+ ⇒ a0 ⇒ a- tilting sequence was rarely observed.
• The dominant octahedral motion was identified as a complex precession-nutation process involving continuous reorientation and oscillations.

Conclusions:

• The findings reveal that halide perovskite octahedra exhibit complex rotational dynamics beyond simple tilting.
• These complex motions are likely prevalent across various halide perovskites, impacting their structural behavior.
• The developed machine-learning approach provides a powerful tool for future investigations and guides experimental efforts to detect these dynamics.