Temperature-Dependent Lattice Dynamics and Vibration Effects in Cs₂UCl₆: Insights from DFT and Machine Learning...

Uranium-based materials show great promise as scintillators in ultraprecise detector application owing to their strong radiation stopping capabilities and excellent spatial resolution. However, the excited-state-driven ultrafast lattice dynamics of uranium compounds remain insufficiently understood. In this study, the lattice dynamics of Cs₂UCl₆ were investigated through density functional theory (DFT) and machine learning (ML). The results indicate that [UCl₆]^4- predominates at high frequencies (>100 cm^-1), which interacts with Cs at low frequencies (<100 cm^-1). The asymmetric stretching (ω₀) and bending (ω₁) octahedral vibrations of [UCl₆]^4- exhibit a high degree of temperature sensitivity, while the ML results indicate nonlinear synergistic effects, especially the disorder of bond angles resulting in the oscillation of the potential energy surface. These findings suggest that the phonon scattering is attributable to the structure distortion of the [UCl₆]^4- complex under asymmetric low-frequency bending vibration, thereby providing theoretical insight for the lattice dynamics behavior and spectral regulation in Cs₂UCl₆.