Application of a deep potential model for the structural evolution and phase stability of thorium

Abstract

Thorium (Th) is an important actinide element for advanced nuclear energy systems, but it undergoes complex phase transitions during heating. Currently, there is no unified force field that adequately describes its various phases, which poses challenges for atomic-scale simulations. This study addresses these challenges by developing and validating a high-fidelity deep potential (DP) model for two phases of Th, including the face-centered cubic phase (α-Th) and the body-centered cubic phase (β-Th). The DP model demonstrates exceptional accuracy in reproducing the fundamental properties of these two phases, such as equations of state, elastic constants, and phonon dispersion curves. Notably, the DP successfully predicts the temperature-induced solid–solid phase transition at 1651 K and the solid–liquid melting transition at 2056 K, showing excellent agreement with experiments. Extensive molecular dynamics simulations further reveal the evolution of key properties across these phases, including behavior related to vacancy formation energy, abrupt changes in self-diffusion coefficients at transition points, and characteristic structural changes highlighted through radial distribution function analysis. Our work establishes a robust and efficient DP-based simulation framework for Th, providing a powerful tool for future molecular dynamics investigations of Th-based materials under a variety of conditions.