Deformation Mechanism for Ice VII

By using force constants for both the hydrogen bond H···O–H and the chemical bond O–H in harmonic and Morse potential energy functions, we have obtained ratios of potential energy to macroscopic work of compression for H2O and D2O ice VII using the experimental P–V data of Holzapfel and Drickamer. The Morse potentials gave values of this ratio quite close to 1.0 even at the highest pressure, viz., 165 kbar for H2O and 220 kbar for D2O ice VII. These models all yield the result that the protons remain on their original oxygen atoms during compression; i.e., there is no proton migration with formation of “symmetric” hydrogen bonds. The isothermal bulk modulus for pressures in the neighborhood of 22 kbar, for both H2O and D2O ice VII, was estimated to be 235 kbar.