Hydrogen bond relaxation dynamics and the associated symmetric, volumetric, vibronic, and phase transitional anomalies of frozen H2O under compression

TL;DR

This paper investigates the microscopic mechanisms behind the anomalous physical properties of ice under compression, focusing on hydrogen bond relaxation, phonon dynamics, and phase transition changes.

Contribution

It introduces a detailed model linking Coulomb repulsion and electron pair interactions to the anomalies observed in frozen water under pressure.

Findings

Hydrogen bond symmetrization occurs under compression.

Phonon frequencies are altered, with softer modes stiffening and stiffer modes softening.

Critical temperature for phase transition shifts with pressure.

Abstract

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.