Temperature-dependent elastic properties of U 3 Si 2 from DFT + U calculations: Reconciling anisotropy with experimental measurements

U₃Si₂ is a promising accident-tolerant nuclear fuel, yet its elastic properties remain poorly understood because of significant discrepancies between experimental measurements, including bulk moduli ranging from ~680.16em0exGPa (RUS) to ~1070.16em0exGPa (XRD), the origin of which has remained unresolved. In this work, we investigate the structural, thermodynamic, and elastic properties of U₃Si₂ from 0 to 1500 K using density functional theory in the DFT+U approach combined with machine-learning-assisted canonical sampling and interatomic potentials. The use of the PBEsol functional and a U value of 2.0 eV enables us to simultaneously suppress the spurious structural distortion of previous calculations and reproduce the experimental equilibrium volume, which is a prerequisite for a reliable determination of the full tetragonal elastic tensor. We further demonstrate that explicit finite-temperature sampling is essential to capture the full thermal softening of the elastic constants, as static calculations at thermally expanded volumes underestimate this effect by up to 30% for certain elastic constants. Finally, we demonstrate that the apparent conflict between high pressure XRD and RUS bulk moduli arises from the pronounced elastic anisotropy of the tetragonal lattice combined with the isotropic approximations used in RUS data analysis and the effects of sample porosity. These findings provide a consistent set of temperature-dependent elastic properties for U₃Si₂ and resolve long-standing discrepancies between experimental measurements.