14 DAY TRIAL // Water may seem simple when we see it like that: H2O, two hydrogen atoms bound to an oxygen one.
Or not?
A research team at the University of Delaware and Radboud University in the Netherlands have employed high-speed computers and physics to peek into the hidden properties of water.
Their novel first-principle simulation of water molecules, employing exclusively quantum physics laws, without experimental data, will bring many scientific and commercial applications, from investigating the behavior of the organic molecules to the design of the next generation of power plants.
"Water as a liquid is not simple at all and has several properties different from most other liquids. For example, a well-known anomaly of water is that its density is highest at four degrees Celsius above the freezing point. Thus, ice floats on water, whereas the solid state of other compounds would sink in their liquids," said lead author Krzysztof Szalewicz, professor of physics and astronomy at the University of Delaware.
Another water specific trait is absorbing large heat amounts before it starts getting hot, heat that is freed slowly during cooling.
This specific thermal behavior ensures that water pools, from puddles to oceans, do not boil during the day or freeze at night, regardless of the season.
These unique traits are linked to the water's molecular structure, which enables its molecules to form hydrogen bonds with the neighboring water molecules.
The hydrogen part of the molecule possesses a slight positive charge, while the oxygen a slight negative one.
"For a long time, most researchers agreed that, in its liquid state, each water molecule coordinates on average with four other water molecules by forming hydrogen bonds," Szalewicz said.
"However, a 2004 paper in Science claimed that this coordination takes place with only two molecules, a discovery that, if correct, would turn over the whole water paradigm."
"The experimental claim was not dismissed right away, because existing theoretical models of liquid water were "parameterized" or coordinated to a specific class of experiments. However, the ambiguities about the structure of liquid water may be resolved if the structure is predicted directly from the laws of physics," Szalewicz said.
This team generated after several months a new theoretical framework for describing the structure and behavior of the water molecule, from a pair of water molecules to liquid water.
"This became possible recently when fast multiprocessor computers enabled very accurate solutions of the equations of quantum mechanics describing the forces that water molecules exert on each other," Szalewicz said.
"Once these forces are known, one can find motions in an ensemble of water molecules and predict all the properties of liquid water. Among its many applications, the research should help scientists better understand water in not only its liquid form, but in other states as well, such as crystalline forms of ice, and water in extreme conditions, including highly reactive "supercritical" water, which is used to remove pollutants in wastewater and recover waste plastic in chemical recycling," Szalewicz said.