Abstract
Liquid water exhibits unconventional behaviour across its wide range of stability – from its unusually high liquid-vapour critical point down to its melting point and below where it reaches a density maximum and exhibits negative thermal expansion allowing ice to float. Understanding the molecular underpinnings of these anomalies presents a challenge motivating the study of water for well over a century. Here we examine the molecular structure of liquid water across its range of stability, from mild supercooling to the negative pressure and high temperature regimes. We use a recently-developed, electronically-responsive model of water, constructed from gas-phase molecular properties and incorporating many-body, long-range interactions to all orders; as a result the model has been shown to have high transferability from ice to the supercritical regime. We report a link between the anomalous thermal expansion of water and the behaviour of its second coordination shell and an anomaly in hydrogen bonding, which persists throughout liquid water’s range of stability – from the high temperature limit of liquid water to its supercooled regime.
Highlights
Liquid water exhibits unconventional behaviour across its wide range of stability – from its unusually high liquid-vapour critical point down to its melting point and below where it reaches a density maximum and exhibits negative thermal expansion allowing ice to float
Water can be vitrified into three types of glasses[4]: low density amorphous (LDA), high density amorphous (HDA) and very high density amorphous (VHDA)[5]
We begin with a study of the second coordination shell, followed by an analysis of the hydrogen bonding connectivity where we show that the asymmetry in hydrogen bonding persists over the whole range of temperatures and pressures studies
Summary
Liquid water exhibits unconventional behaviour across its wide range of stability – from its unusually high liquid-vapour critical point down to its melting point and below where it reaches a density maximum and exhibits negative thermal expansion allowing ice to float. We examine the molecular structure of liquid water across its range of stability, from mild supercooling to the negative pressure and high temperature regimes. We report a link between the anomalous thermal expansion of water and the behaviour of its second coordination shell and an anomaly in hydrogen bonding, which persists throughout liquid water’s range of stability – from the high temperature limit of liquid water to its supercooled regime. The standard picture postulates that water anomalies arise from a competition[3] between two local structures: a low-density, ordered structure and a high-density, disordered one. The evidence for this picture comes from both experiment and simulation. D5 can be used as a discriminator[17] between low density and high density phases in a thermodynamic model of liquid water
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