Two Dimensional Ice from First Principles: Structures and Phase Transitions.

Ji Chen,Georg Schusteritsch,Chris J Pickard,Christoph G Salzmann,Angelos Michaelides

doi:10.1103/physrevlett.116.025501

Abstract

Despite relevance to disparate areas such as cloud microphysics and tribology, major gaps in the understanding of the structures and phase transitions of low-dimensional water ice remain. Here, we report a first principles study of confined 2D ice as a function of pressure. We find that at ambient pressure hexagonal and pentagonal monolayer structures are the two lowest enthalpy phases identified. Upon mild compression, the pentagonal structure becomes the most stable and persists up to ∼2 GPa, at which point the square and rhombic phases are stable. The square phase agrees with recent experimental observations of square ice confined within graphene sheets. This work provides a fresh perspective on 2D confined ice, highlighting the sensitivity of the structures observed to both the confining pressure and the width.

Highlights

Despite relevance to disparate areas such as cloud microphysics and tribology, major gaps in the understanding of the structures and phase transitions of low-dimensional water ice remain
Almost every specific system examined has revealed a different structure such as a 2D overlayer built from heptagons and pentagons on a platinum surface or the square ice observed within layers of graphene [8,10]
Using transmission electron microscopy (TEM), square ice structures from a single up to a few layers were observed in such graphene nanocapillaries [10]

Summary

Introduction

Despite relevance to disparate areas such as cloud microphysics and tribology, major gaps in the understanding of the structures and phase transitions of low-dimensional water ice remain. We find that at ambient pressure hexagonal and pentagonal monolayer structures are the two lowest enthalpy phases identified. Force field simulations performed as part of the same study of confined water in graphene layers reproduced some aspects of the experiments, such as the square monolayer ice structure.

Results

Conclusion