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.