Location of water's liquid-liquid critical point · revision history

Revision 2

Accepted · core change · record

Changes against revision 1:

Title
Location of water's liquid-liquid critical point
Plain
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 · changed · core
Revision 1: 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.
Revision 2: Assuming the LLCP exists, determine $(T_{c}, P_{c})$ for $\mathrm{H_2O}$. Published model results and extrapolations from experiment span roughly $T_{c} = 170 \text{ to } 230\,\mathrm{K}$ and $P_{c}$ from about $0 \text{ to } 2 \times 10^{9}\,\mathrm{dyn}/\mathrm{cm}^{2}$ ($0 \text{ to } 2\,\mathrm{kbar}$), all approximate. An answer is a measured or reliably computed $(T_{c}, P_{c})$ with error bars, consistent with thermodynamic data at accessible conditions.
Settled by
Experimental location of the LLCP, or first-principles simulations including nuclear quantum effects whose predictions match measured response functions of supercooled water.
Kind
well-posed
Answer type
value
References
(empty)
Literature status
open
Status 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.
Posed since
(empty)

Decisions