LAUSR

Abstract A set of concepts cultivated in the past decade has substantiated the understanding of water ice compression. The concepts include the coupled hydrogen bond (O:H–O) segmental cooperativity, segmental specific-heat disparity, compressive O:H–O symmetrization and polarization, and quasisolidity. Computational and spectrometric outcome consistently justifies that the intromolecular H–O bond has a negative compressibility while the intermolecular O:H nonbond does contrastingly because of the involvement of the interionic O O repulsive coupling. Compression lowers the melting point Tm (named regelation) and raises the freezing temperature TN (for instant ice formation) by inward shifting the quasisolid phase boundary through Einstein's relation, ΔΘDx ∝ Δωx, which is in contrast to the effects of electrostatic polarization and water molecular undercoordination. Theoretical reproduction of the phase boundaries in the phase diagram revealed that H–O bond relaxation dictates boundaries of negative slope, dTC/dP   0. O:H–O bond frozen governs boundaries of constant TC such as the IC-XI boundary and the H–O and O:H energy compensation yields those of constant PC such as X-VII/VIII boundaries. The O O repulsion opposes compression minimizing the compressibility. Polarization enlarges the bandgap and the dielectric permittivity of water ice by raising the nonbonding states above the Fermi energy. Progress evidences the efficiency and essentiality of the coupled O:H–O bonding and electronic dynamics in revealing the core physics and chemistry of water ice, which could extend to other molecular crystals such as energetic materials.