Ab initio investigation of hydrogen bonding and electronic structure of high-pressure phases of ice

TL;DR

This study uses ab initio methods to explore the structural, electronic, and bonding changes in high-pressure ice phases, revealing a linear band gap increase in ice X and a new symmetric-asymmetric hydrogen bond structure in ice XV at extreme pressures.

Contribution

It provides a detailed theoretical analysis of high-pressure ice phases, including the discovery of a new hydrogen-bonding structure, ice XV, and insights into electronic structure evolution under pressure.

Findings

Band gap of ice X increases linearly with pressure.

Valence bands shift to lower energies, conduction bands shift higher.

Identification of a new ice XV phase with symmetric and asymmetric hydrogen bonds.

Abstract

We report a detailed ab initio investigation on hydrogen bonding, geometry, electronic structure, and lattice dynamics of ice under a large high pressure range, including the ice X phase (55-380GPa), the previous theoretically proposed higher-pressure phase ice XIIIM (Refs. 1-2) (380GPa), ice XV (a new structure we derived from ice XIIIM) (300-380GPa), as well as the ambient pressure low-temperature phase ice XI. Different from many other materials, the band gap of ice X is found to be increasing linearly with pressure from 55GPa up to 290GPa, the electronic density of states (DOS) shows that the valence bands have a tendency of red shift (move to lower energies) referring to the Fermi energy while the conduction bands have a blue shift (move to higher energies). This behavior is interpreted as the high pressure induced change of s-p charge transfers between hydrogen and oxygen. It is found that ice X exists in the pressure range from 75GPa to about 290GPa. Beyond 300GPa, a new hydrogen-bonding structure with 50% hydrogen atoms in symmetric positions in O-H-O bonds and the other half being asymmetric, ice XV, is identified. The physical mechanism for this broken symmetry in hydrogen bonding is revealed.