23 Apr 2020
Water molecules organize themselves into boat-shaped hexamers on metal surfaces. This is the conclusion of a theoretical study that claims to have resolved a long-standing gap between experimental results – which appeared to show flat hexamers – and theoretical predictions of a chair conformation.
The water is weird. Its unusual properties have led some researchers to consider it as two different liquids instead of a homogeneous material. In 2002, chemists discovered that thin layers of water form regular hexamers on hydrophobic metals like copper at low temperatures. In the scanning tunneling microscope (STM) images, these structures appeared flat. But theoretical calculations by several teams later showed that a chair-like adsorption configuration was more stable than a flat hexamer.
A team of scientists in China and Sweden now believe they’ve solved the water puzzle, showing that a boat-shaped hexamer not only matches the experimental result, but is actually less energetic than the chair conformation. .
The team simulated STM images through ab initio molecular dynamics. It was only for the configuration of the boat that they showed the same stretched out, C2 symmetrical hexagon seen in the experiments. Further calculations have confirmed that the boat’s configuration is a minimum overall electronic energy, meaning it is more stable than the chair or the flat hexamer.
A better understanding of how water interacts with surfaces could help researchers design materials whose properties change in the presence of water.