Describing Ice from First Principles: Sigbjørn Bore Rounds Off His Stay at CAS

Ice plays a fundamental role on Earth, from its presence in the polar regions to its influence on global climate and sea levels. Yet even the most advanced theoretical models still struggle to predict when and how ice melts.

Physicist Sigbjørn Bore has spent the autumn at CAS as a short-term fellow — a scheme that offers former CAS PIs the opportunity to focus on their research and further advance their CAS projects. Bore first came to CAS in 2023 as a Young CAS PI, leading the project “Can Ice be Described from First Principles?” . This autumn, he has returned to build on that work by improving theoretical models of ice through empirical corrections that bridge the gap between theory and experiment. 

Continuing the work 

“When the Young CAS project ended, the science did not,” Bore says. “We still have loose ends we want to tie up and promising leads to follow up on. Sitting together in the same room and working closely on a single project is a very efficient and motivating way to achieve our goals.”

The first part of his stay was spent writing and submitting a European Research Council (ERC) application. After that, he turned his full attention to the science. “We have had two visitors,” he explains. “First, Andreas Gruneis from Vienna University of Technology, who leads one of about two groups worldwide in periodic coupled-cluster calculations. This is a method that has very high accuracy and can be applied to solids such as ice. Second, Jürgen Gauss is currently a visitor, a world authority on coupled-cluster calculations, but in a different setting: molecules in vacuum.”

While the methods used by Gauss cannot be applied directly to solid ice, they are more accurate for small molecular fragments. “We’re now working on extracting the energy of ice from such calculations,” says Bore. “By the end of the last week, we will have exciting results on ice.”

Focus You Can’t Get on Zoom

For Bore, one of the strengths of CAS is the combination of focus and collaboration that the environment enables. “CAS isolates researchers, directing their efforts to a single research project,” he says. “The longer we stay, the more the world outside disappears, leading to focus.”

He adds that working side by side creates a kind of collaboration that online meetings can’t replace. “Inviting researchers for stays is very different than a Zoom chat. Working in the group rooms, we get to see how each other work. For example, from watching Gruneis work, I came to appreciate spreadsheets, which I never used, to get a feeling of the data, even though it can be slower. With Gauss, we can ask any question about coupled-cluster calculations, and he will have a reasonable answer. Without this, we would many times walk in the dark.”

Bore emphasises that the concentrated time at CAS has been essential for advancing the project. “The isolation and focus are the best aspects, driving all forces in one direction,” he says. “This is very powerful for scientific advances.”

He also notes that the experience has had a lasting effect on his research direction. “Scientifically, my research has focused more on accurate ice modelling, using exotic methods I would probably not have been able to explore otherwise. I have also gained new collaborations that I would not have otherwise had, such as with Professor Gauss and Professor Gruneis. This was the first project I ever led, and I have grown a lot in this responsibility.”

Looking ahead

As Bore wraps up his stay, he leaves CAS with new results and strengthened collaborations that continue the work started through the Young CAS Grant programme. “CAS has played a huge role in my research,” he says. “It has given me the time, space, and collaborations to pursue questions I could not have explored otherwise.”

Don’t miss our earlier “Meet the Project” interview with Bore from when he first began his Young CAS project.