by josh perry, editor
scientists from ibm research and the u.k. science and technology facilities council (stfc) hartree center have created new simulation techniques for predicting the properties of new materials and expanding the conditions in which these predictions at the molecular level can be made with confidence.
an illustration showing how water molecules are arranged in the liquid around a central reference molecule. (ibm research)
according to a post from ibm, the researchers incorporated electronic responses into the molecular conditions, which allowed the molecules to adapt to the environment as they naturally do and also opened simulations up to complex systems.
“we address the celebrated challenge of liquid water as a model system exhibiting unusual and dramatic changes to physical properties depending on temperature – with particularly mysterious behavior (such as a temperature of maximum density and negative thermal expansion) appearing near and below freezing,” wrote jason crain on the ibm research blog.
he added, “our team uses materials simulation to explore the structure and properties of water at the extremes of its stability range as a liquid: at its high temperature limit when the liquid first condenses into small molecular-scale chains and droplets down to the lowest temperatures reachable for the highly structured ‘supercooled’ liquid – which survives far below the normal freezing point; and into the unfamiliar ‘stretched’ regime – where the liquid bonds support high tensile stresses before ‘breaking’ to form vapor cavities.”
researchers are confident that this model will work for solid materials as well as for liquids and they are working to make this technique applicable for industrial conditions, including the life sciences.
the research was recently published in scientific reports. the abstract stated:
“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.”