While liquids seem to be formless masses that flow without structure, the illustration above shows some of the complex patterning present inside liquid water.
In particular, it reveals how water molecules are arranged in the liquid around a central reference molecule. The H2O molecule is shown with a large central oxygen atom in red flanked by a pair of smaller white hydrogen atoms.
The white areas show the highly directional organisation of water density in the first and second structural ‘shells’ arising from the hydrogen bonds, while the orange areas show the depletion regions where no water molecules can reside.
The image was obtained using the quantum Drude oscillator model, which describes how atoms and molecules can be polarised in the presence of an electric field.
It was created during a detailed modelling exercise of the behaviour of liquid water, which exhibits dramatic and unusual changes to its physical properties with changing temperature, particularly near the freezing point.