Hydrogen bonds and van der Waals forces in ice at ambient and high pressures

TL;DR

This study uses first principles methods to analyze the balance between van der Waals forces and hydrogen bonds in ice, revealing how their contributions change under pressure and impact phase transition predictions.

Contribution

It demonstrates the importance of including van der Waals forces in DFT calculations to accurately predict ice phase transition pressures.

Findings

vdW forces increase with pressure in ice

H bonding contribution decreases at high pressure

Neglecting vdW leads to overestimated transition pressures

Abstract

The first principles approaches, density functional theory (DFT) and quantum Monte Carlo, have been used to examine the balance between van der Waals (vdW) forces and hydrogen (H) bonding in ambient and high pressure phases of ice. At higher pressure, the contribution to the lattice energy from vdW increases and that from H bonding decreases, leading vdW to have a substantial effect on the transition pressures between the crystalline ice phases. An important consequence, likely to be of relevance to molecular crystals in general, is that transition pressures obtained from DFT functionals which neglect vdW forces are greatly overestimated.