Experts Study Properties Of Smallest Water Droplets

Brett Smith for – Your Universe Online

Using computer modeling, researchers at the University of California, San Diego and Emory University have revealed new details surrounding hexamer structures that are considered to be the smallest droplets of water.

“Ours are the first simulations that use an accurate, full-dimensional representation of the molecular interactions and exact inclusion of nuclear quantum effects through state-of-the-art computational approaches,” explained study author Joel Bowman, a professor with Emory University’s Department of Chemistry.

“These allow us to accurately determine the stability of the different isomers over a wide range of temperatures ranging from 0 to 150 Kelvin.”

The team´s report, which was recently published in The Journal of the American Chemical Society (JACS), has implications for many areas of science, including fields as diverse as pharmacology and climate change research.

“About 60% of our bodies are made of water that effectively mediates all biological processes,” said Francesco Paesani, a co-author who is an assistant professor in the Department of Chemistry and Biochemistry at UC San Diego.

“Without water, proteins don’t work and life as we know it wouldn’t exist. Understanding the molecular properties of the hydrogen bond network of water is the key to understanding everything else that happens in water. And we still don’t have a precise picture of the molecular structure of liquid water in different environments.”

Scientists consider the water hexamer to be the smallest droplet of water because it is the smallest configuration of water molecules that is three dimensional. The interactions between hexamers can change according to temperature, resulting in the formation of ice, water or vapor. In the newest report, researchers have determined the ratios of different water hexamer configurations, such as the ℠cage´, ℠book´ or ℠prism´, at different temperatures, or kinetic energies.

To perform the data-intensive calculations, the research team turned to UC San Diego´s Gordon supercomputer. The computer uses a vast amount of flash memory to expedite processes that could be constrained by slower-spinning disk memory.

Using Gordon and Triton, UC San Diego´s high-powered computer cluster, to conduct the data-intensive models, researchers identified the prism isomer as the global minimum-energy structure. However, the quantum simulations showed that both the cage and prism isomers are present in nearly equal amounts at very low temperatures. As the modeling temperatures increased, more cages and book structures began to emerge.

“Our simulations took full advantage of Gordon distributing the computations over thousands of processors,” said Volodymyr Babin, a researcher with UC San Diego’s Department of Chemistry and Biochemistry. “That kind of parallel efficiency would be hardly achievable on a commodity cluster. The scalability of our computational approach stems from the combination of a state-of-the-art simulation technique (replica-exchange) with path-integral molecular dynamics.”

The report noted that the computer models generated results that were very consistent with previous experiments, which used broadband rotational spectroscopy.

According to Babin, the team plans to continue working with this methodology to study the microscopic origins of the unusual properties of liquid water and ice. He added that leveraging the power of UC San Diego´s supercomputers allows them to calculate the huge number of data-intensive quantum chemistry computations.