BIO In the literature: open

Location of water's liquid-liquid critical point

In plain words

If water's second critical point exists, its temperature and pressure must be pinned down. Model estimates disagree by tens of kelvin and by thousands of atmospheres.

Precise statement

Assuming the LLCP exists, determine $(T_{c}, P_{c})$ for H2O. Published model results and extrapolations from experiment span roughly $T_{c} = 170 \text{ to } 230\,\mathrm{K}$ and $P_{c}$ from about $0 \text{ to } 2e9\,\mathrm{dyn}/\mathrm{cm}^{2}$ ($0 \text{ to } 2\,\mathrm{kbar}$), all approximate. An answer is a measured or reliably computed $(T_{c}, P_{c})$ with error bars, consistent with thermodynamic data at accessible conditions.

What would settle it

Experimental location of the LLCP, or first-principles simulations including nuclear quantum effects whose predictions match measured response functions of supercooled water.

Status in the literature

Unverified note

A 2026 ultrafast X-ray experiment placed the critical temperature near $210 \pm 8\,\mathrm{K}$ (You et al., Science 2026); the critical pressure and an independent confirmation remain open.