Regions of stability for LDA, HDA, and VHDA amorphous ices

Abstract

Model structures have been created for ice Ih and for low density (LDA), high density (HDA), and very high density (VHDA) amorphous ices using the procedure for determining the equilibrium configurations of molecules in amorphous phases. The chemical potentials of these ices were calculated for wide ranges of temperature and pressure. The curves of equilibrium phase transitions have been plotted. It is shown that at high pressures, VHDA ice is more stable than Ih, while HDA ice is metastable with respect to VHDA over the whole range of pressures and temperatures. These calculations provide an explanation to the experimentally observed transition of HDA into a higher density phase (VHDA) during isobaric heating.