An estimate for the Gibbs energy of amorphous solid waters and differences between the low-density amorph and glassy water

Molar volume and compressibility of the high density amorph (HDA) and of hexagonal ice (ice Ih) were measured at 77 K and high pressures, and the Gibbs energy, G, of HDA and of the low density amorph (LDA) calculated from their volume–pressure integrals. The relative magnitudes of their G predict that a step increase from ∼3 to ∼7 kbar will transform LDA at 77 K to ice Ih, not to HDA. The excess G of LDA over ice Ih is 1.6±0.1 kJ mol−1, which is higher than the experimentally determined value of 1.1±0.1 kJ mol−1 for amorphous solid water [J. Chem. Phys. 105, 240 (1996)]. A path for the volume in the pressure plane needed to satisfy the requirement of 1.1±0.1 kJ mol−1 was not found. These suggest that LDA is different from the amorphous solid or glassy water, which is consistent with the findings by other methods, thus calling into question the inferences [Nature (London) 392, 164 (1998)] based on a thermodynamic continuity between LDA and supercooled water.