Temperature-Driven Structural Phase Transitions in SmNiO₃: Insights from Molecular Dynamics Simulations

The metal-insulator transition (MIT) in rare-earth nickelates exemplifies the intricate coupling between lattice dynamics and electronic effects. This strong interplay makes it challenging to disentangle their individual roles in driving the transition in RNiO₃. Here, we investigate the structural contribution to the phase transition by employing molecular dynamics (MD) simulations based on a machine-learned interatomic potential with DFT+U-level accuracy, where electronic degrees of freedom are not explicitly included. Taking SmNiO₃ as a prototypical system, our simulations show that the structural phase transition is intrinsically temperature-driven and occurs spontaneously via collective lattice distortions. The simulated critical temperature is 340 K and can be further tuned by pressure. These findings provide atomistic insights into the understanding of structural evolution underlying the phase transition and suggest a cooperative interplay between lattice and electronic mechanisms in driving the MIT in RNiO₃.