Signature properties of water: Their molecular electronic origins

Vlad P. Sokhan; Andrew P. Jones; Flaviu S. Cipcigan; Jason Crain; Glenn J. Martyna

doi:10.1073/pnas.1418982112

New Research In

Edited by Paul Madden, University of Oxford, Oxford, United Kingdom, and accepted by the Editorial Board March 31, 2015 (received for review October 1, 2014)

Significance

Water is one of the most common substances yet it exhibits anomalous properties important for sustaining life. It has been an enduring challenge to understand how a molecule of such apparent simplicity can encode for complex and unusual behavior across a wide range of pressures and temperatures. We reveal that embedding a complete hierarchy of electronic responses within the molecule allows water’s phase behavior and signature properties to emerge naturally even within a simple model. The key result is a simple and accurate, prediction of liquid–gas phase equilibria from freezing to the critical point thus establishing a direct link between molecular and condensed phase properties and a sound physical basis for a conceptually simple but broadly transferable model for water.

Abstract

Water challenges our fundamental understanding of emergent materials properties from a molecular perspective. It exhibits a uniquely rich phenomenology including dramatic variations in behavior over the wide temperature range of the liquid into water’s crystalline phases and amorphous states. We show that many-body responses arising from water’s electronic structure are essential mechanisms harnessed by the molecule to encode for the distinguishing features of its condensed states. We treat the complete set of these many-body responses nonperturbatively within a coarse-grained electronic structure derived exclusively from single-molecule properties. Such a “strong coupling” approach generates interaction terms of all symmetries to all orders, thereby enabling unique transferability to diverse local environments such as those encountered along the coexistence curve. The symmetries of local motifs that can potentially emerge are not known a priori. Consequently, electronic responses unfiltered by artificial truncation are then required to embody the terms that tip the balance to the correct set of structures. Therefore, our fully responsive molecular model produces, a simple, accurate, and intuitive picture of water’s complexity and its molecular origin, predicting water’s signature physical properties from ice, through liquid–vapor coexistence, to the critical point.

Footnotes

↵¹To whom correspondence should be addressed. Email: vlad.sokhan{at}npl.co.uk.

Author contributions: V.P.S., J.C., and G.J.M. designed research; V.P.S. and F.S.C. performed research; V.P.S., A.P.J., F.S.C., J.C., and G.J.M. analyzed data; V.P.S., A.P.J., F.S.C., J.C., and G.J.M. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission. P.M. is a guest editor invited by the Editorial Board.