Two structures of liquid water

Parameter-free RealQM probe — LDL vs HDL, 64 waters

Temperature: 230 K 270 K 300 K 340 K 380 K

Reset histogram confine to liquid density

▶ Auto cool-sweep 380→220 K ■ stop

LDL fraction & mean q vs temperature — the two-state prediction is that the tetrahedral (LDL) side grows as water cools.

How to read it. Two peaks in q (tetrahedral order) or in d5 (5th-neighbour distance) = two coexisting local structures. Cooling should grow the high-q / large-d5 (LDL) side.

Caveats. Coarse geometry (~5%); only interior-core oxygens analysed (free surface excluded); Brownian model-time, not real kinetics; 64 waters is small for statistics; q/d5 thresholds indicative.
Confinement. The unconfined vacuum droplet disperses (coordination → 0), so a disclosed soft spherical wall holds it near liquid density. It imposes only the average density, not local structure — so the two-structures question stays fair. Watch the density check: with the wall on, nearest O–O should recover toward ~2.8 Å and coordination toward ~4. Exploratory throughout.