Microstructure and Transport Properties of CaCl2–CaI2 Molten Salt: A First-Principles Molecular Dynamics Study

In this study, first-principles molecular dynamics (FPMD) simulations were employed to systematically investigate the effects of temperature and composition on the microstructure and transport properties of CaCl2–CaI2 mixed molten salts at the atomic scale. Structural analysis shows that the system exhibits good relaxation behavior and thermodynamic stability, with coordination strength following Ca-Cl > Ca-I. The transport properties reveal a coupled dependence on temperature and composition: increasing CaI2 content enhances the diffusion of I− ions, whereas at 1173 K, a decrease in diffusion coefficients is observed for all ionic species. Arrhenius analysis indicates that increasing CaI2 content lowers the activation energy for ion migration. The shear viscosity follows the order η(Ca2+) > η(Cl−) ≥ η(I−), and decreases with increasing temperature and CaI2 concentration, indicating improved fluidity. Notably, the results reveal a competitive coordination mechanism between Cl− and I− around Ca2+, as well as a non-monotonic transport behavior at high temperatures, reflecting the complex coupling between composition and ionic dynamics in mixed halide melts. This study provides a theoretical basis for the optimization of molten salt electrolysis processes and nuclear energy materials, and offers insight for future multiscale simulations and experimental validation.