And Yet It Moves: LiNiO2, a Dynamic Jahn–Teller System

The dynamics of Jahn–Teller distortions in LiNiO2 is revealed by ab initio molecular dynamics simulations combined with statistical analyses. Jahn–Teller distortions have been observed on a local scale, but the system was always identified as a perfectly undistorted rhombohedral structure isostructural with LiCoO2. On the contrary, static calculations consistently predicted the existence of a monoclinic structure. Here, we show that Jahn–Teller distortions indeed take place but reorient dynamically when temperature is applied. Correlation analysis reveals that while cooperativity can survive within one layer, correlation between different layers is for all practical purposes nonexistent. The continuous reorientation of the Jahn–Teller direction combined with noncooperativity between layers prevents the system from undergoing a macroscopic monoclinic shear, giving LiNiO2 the familiar, apparent R3̅m symmetry.