Hydrogen Ordering in Ice Ih Facilitates the Transition from HDA to Ice XII

Under low-temperature compression, ice I becomes metastable
but
does not transform into other high-pressure ice crystals. Excess pressure
results in its collapse to high-density amorphous ice (HDA), which
predominantly transforms into ice IV or XII upon heating. Understanding
how to avoid pressure-induced amorphization and molecular origin prioritizing
nucleation of a metastable phase provides insights into the nature
of HDA. Here, we perform molecular dynamics (MD) simulations to demonstrate
that when hexagonal ice (ice Ih) exhibits a particular hydrogen ordering,
the hydrogen-ordered ice Ih can transform into ice XII via a partially
ordered HDA. The crystalline region is identified as an unreported
ice form (named ice M) with pentagonal-helical hydrogen-bond networks
identical to those in ice XII. The remanent ice M configuration facilitates
the transition of HDA to ice XII. Combined with our previous study
on a hydrogen-ordered form of ice Ic, hydrogen ordering in ice I appears
to enable crystal-to-crystal transitions, whether direct or indirect,
even at low temperatures.