  Coulomb repulsion between the unevenly-bounded bonding "-" and nonbonding ":"
electron pairs in the "O2- : H+/p-O2-" hydrogen-bond is found to originate the
anomalies of low-compressibility, phonon relaxation dynamics, proton
symmetrization in the hydrogen-bond, and the change of the critical temperature
for the VIII-VII phase transition of ice under compression. The resultant force
of the compression, the repulsion, and the uneven binding strength of the
electron pairs make the softer intermolecular "O2- : H+/p" nonbonding lone pair
be highly compressed and stiffened but the stiffer intramolecular "H+/p-O2-"
bond be elongated and softened. Consequently, the softer nonbond phonons (< 400
cm-1) are stiffened and the stiffer bond phonons (> 3000 cm-1) are softened
upon compression. The nonbond compression and the real bond elongation results
in the O2--H+/p : O2- symmetrization and the low compressibility of ice.
Findings should form the starting point to unveil the physical anomalies of H2O
under various stimuli.
