Is It Possible to Follow the Structural Evolution of Water in "No-Man's Land" Using a Pulsed-Heating Procedure?

The anomalous increase in compressibility and heat capacity of supercooled water has been attributed to its structural transformation of into a four-coordinated liquid. Experiments revealed that κ T and C p peak at T W thermo ≈ 229 K [Kim et al. Science 2017 , 358 , 1589; Pathak et al. Proc. Natl. Acad. Sci. 2021 , 118 , e2018379118]. Recently, a pulsed heating procedure (PHP) was employed to interrogate the structure of water, reporting a steep increase in tetrahedrality around T W PHP = 210 ± 3 K [Kringle et al. Science 2020 , 369 , 1490]. This discrepancy questions whether water structure and thermodynamics are decoupled, or if the shift in T W is an artifact of PHP. Here we implement PHP in molecular simulations. We find that the stationary states captured at the bottom of the pulse are not representative of the thermalized liquid or its inherent structure. Our analysis reveals a temperature-dependent distortion that shifts T W PHP to ∼20 K below T W thermo . We conclude that 2 orders of magnitude faster rates are required to sample water's inherent structure with PHP.