Coupling between structural evolution and glass transition in supercooled water

Abstract Water exhibits unique structural, thermodynamic, and dynamic anomalies, particularly in supercooled states where structural evolution between high- and low-density liquid environments occurs alongside kinetic arrest. Here we use molecular dynamics simulations of TIP4P/2005 model of water with cooling and heating scan rates from 10 to 3000 K µs⁻¹ to investigate equilibrium and nonequilibrium behavior. Above ~ 220 K, properties are scan-rate independent, indicating equilibrium, while below this temperature kinetic effects dominate on the simulations time scale, reflecting glassy dynamics. In the liquid regime, the temperature dependence of viscosity reveals two relaxation mechanisms with distinct activation energies. The rapid slowing down of the lower-temperature mechanism leads to the onset of the glass transition. At the cooling and heating rates accessible to the present simulations, the glass transition occurs in the same temperature range as the heat-capacity maximum associated with the gradual structural evolution between high- and low-density liquid environments. By integrating a two-state thermodynamic model with the Tool–Narayanaswamy–Moynihan glass-transition framework, we separate equilibrium anomalies from kinetic glass-transition effects. This combined structural evolution – glass transition (SE-GT) approach provides a consistent description of water’s coupled thermodynamic and dynamic behavior across a broad temperature range.