2026/04/01 by Florian Pabst, Ali Hassanali
#cond-mat.soft
The origin of water's anomalous behavior remains a central open problem in the physical sciences and is often attributed to a liquid-liquid transition (LLT) between high- and low-density liquid states deep in the supercooled regime. Experimental access to this region has been challenging due to rapid crystallization, leaving atomistic simulations as a major source of supporting evidence. Using extensive machine-learning-accelerated first-principles simulations in direct comparison with spectroscopic, structural, and dynamical experimental measurements, we show that features commonly interpreted as signatures of two-liquid behavior coincide with the onset of dramatic dynamical slowing down characteristic of an emerging non-ergodic glassy state. Specifically, we find that two-state fluctuations associated with an LLT reflect a transformation from a high-density liquid to a kinetically constrained low-density glassy-like state. By mapping equilibrium dynamics across pressure and temperature, our results suggest a reassessment of water's metastable landscape, in which the reported two-state behavior may reflect a relatively high glass-transition temperature of low-density water, 189 ± 8 K -- curiously close to the temperature commonly associated with the proposed LLT.