Atomic-scale insights into melting and supercooling mechanism of sodium acetate trihydrate via molecular dynamics

Sodium acetate trihydrate (SAT) is a promising phase change material for thermal energy storage through phase transition, yet its microscopic mechanisms of phase transition, especially melting and intrinsic supercooling, remain unclear. In this study, all-atom molecular-dynamics simulations were performed to elucidate the melting pathway, supercooling mechanism, and facet-dependent stability of SAT. The analysis of melting dynamics reveals a three-stage transition comprising interfacial relaxation, melting-front propagation, and liquid stabilization. Melting is driven by the breakdown of long-range ionic order and the reorganization of water molecules into a bulk hydrogen-bonded network, where H_{2}O-H_{2}O interactions transform from repulsive to attractive. Under isothermal conditions, liquid SAT remains metastable down to 220 K without crystallization during 1000 ns. The energetic decomposition reveals a dual stabilization mechanism: (i) electrostatic trapping arising from strengthened Na^{+}-CH_{3}COO^{-} pairing and enhanced short-range charge correlations, and (ii) ion-water cooperative stabilization that locks hydration shells and slows the reorientation of water molecules. These effects produce a polarized yet dynamically constrained liquid network, in which the number of hydrogen bonds increases while their collective electrostatic coherence weakens. Comparative simulations of the (402), (-402), and (062) crystal planes further reveal distinct interfacial energetics and hydrogen-bond organizations, with the (402) facet exhibiting the strongest interfacial stability and the (062) facet showing diffuse hydration and weak lattice cohesion.