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Origin of dielectric polarization suppression in confined water from first principles.

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Peer-reviewed

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Abstract

It has long been known that the dielectric constant of confined water should be different from that in bulk. Recent experiments have shown that it is vanishingly small, however the origin of the phenomenon remains unclear. Here we used ab initio molecular dynamics simulations (AIMD) and AIMD-trained machine-learning potentials to understand water's structure and electronic properties underpinning this effect. For the graphene and hexagonal boron-nitride substrates considered, we find that it originates in the spontaneous anti-parallel alignment of the water dipoles in the first two water layers near the solid interface. The interfacial layers exhibit net ferroelectric ordering, resulting in an overall anti-ferroelectric arrangement of confined water. Together with constrained hydrogen-bonding orientations, this leads to much reduced out-of-plane polarization. Furthermore, we directly contrast AIMD and simple classical force-field simulations, revealing important differences. This work offers insight into a property of water that is critical in modulating surface forces, the electric-double-layer formation and molecular solvation, and shows a way to compute it.

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Acknowledgements: The authors thank D. V. Matyushov for fruitful discussions. T. D. and L. F. were supported by the European Research Council (grant 819417) under the European Union Horizon 2020 Research and Innovation Programme. A. M. acknowledges support from the European Union under the “n-aqua” European Research Council project (grant 101071937). C. S. acknowledges partial financial support from the Alexander von Humboldt-Stiftung and the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) project number 500244608. J. C. and A. M. thank Beijing Municipal Natural Science Foundation (no. JQ22001) for support. We are grateful to the UK Materials and Molecular Modelling Hub for computational resources, which is partially funded by EPSRC (EP/P020194/1 and EP/T022213/1), and computational support from the UK national high performance computing service, ARCHER, for which access was obtained via the UKCP consortium, funded by EPSRC grant ref. EP/P022561/1. We are also grateful to the Research IT and the use of the High Performance Computing (HPC) Pool funded by the Research Lifecycle Programme at the University of Manchester.

Keywords

3403 Macromolecular and Materials Chemistry, 34 Chemical Sciences

Journal Title

Chem Sci

Conference Name

Journal ISSN

2041-6520
2041-6539

Volume Title

Publisher

Royal Society of Chemistry (RSC)
Sponsorship
Beijing Municipal Natural Science Foundation (JQ22001)
Deutsche Forschungsgemeinschaft (500244608)
H2020 European Research Council (101071937, 819417)
Engineering and Physical Sciences Research Council (EP/P020194/1, EP/P022561/1, EP/T022213/1)
Alexander von Humboldt-Stiftung (Unassigned)