Imagine you have two window screens. If you place a second screen in front of the first, and then twist it, you’ll notice patterns emerge – these are moiré patterns. If each of the overlapping screens were actually a single sheet of atoms, a bilayer, the resulting moiré pattern that comes from twisting these layers is far more than just a visual spectacle – the pattern is indicative of changes in energy, and electron behavior. If we could harness these changes, like those that block heat, it could lead to a number of positive impacts, like protecting spacecraft, improving home energy efficiency and preventing electronics from overheating as they get smaller and more powerful. A team of researchers from the University of Illinois (U. of I.) used the U.S. National Science Foundation ACCESS program to get a clearer picture of exactly how twisted bilayers work.
U. of I. professors Pinshane Huang, materials science and engineering, and Elif Ertekin, mechanical science and engineering, teamed up on this project. They used computer simulation and microscopic imaging to learn more about how the atoms in twisted bilayers operate. To do that, they needed resources capable of rapidly simulating on the atomic level.
The team, which included Yichao Zhang, a post-doctoral researcher at Illinois during the research phase, and now a professor at the University of Maryland, used two distinct resources for their work. With ACCESS allocations, researchers can use a number of resources to complete their work – in this case, the team utilized the National Center for Supercomputing’s (NCSA) Delta and Pittsburgh Supercomputing Center’s (PSC) Bridges-2.
“Mapping phasons in moiré superlattices requires exceptional spatial resolutions enabled by electron ptychography,” said Zhang. “This computation-aided microscopy technique relies on high-performance computing to achieve the resolution needed for thermal vibration mapping. Thanks to the computational power of NCSA Delta, we drastically reduced reconstruction times and accelerated optimization of reconstruction parameters. Comparison with simulations validated our experimental observation. This allows us to map thermal vibrations atom by atom, which is a breakthrough that wouldn’t have been possible without such advanced resources.”
We rely on Bridges-2 a lot for the work in our group … We do all sorts of atomistic simulations, sometimes at the quantum level of theory and sometimes classical. In this work, we used classical molecular dynamics simulations, which show the time dynamics of atoms vibrating. So [we are] using Bridges to help us integrate equations of motion, to tell us microscopically about the way that materials behave, and why they behave the way that they behave more or less directly from solving fundamental equations … And it would be really hard to do the things we do without Bridges.
—Elif Ertekin, University of Illinois
For a more detailed explanation of this research, you can visit the original story here: New Heat-Conducting Behaviors Appear in “Twisted Bilayers”
If you’re in need of high-performance computing resources for your next project – even if you might need more than one supercomputer to do the job – you can start the allocation process today. Researchers and educators who get an allocation through ACCESS can choose from a wide range of HPC needs, from storage to CPUs and GPUs; ACCESS can help power your research at no additional cost to you.
Resource Provider Institution(s): Pittsburgh Supercomputing Center (PSC), National Center for Supercomputing Applications (NCSA)
Resources Used: Bridges-2, Delta
Affiliations: University of Illinois
Funding Agency: NSF
Grant or Allocation Number(s): MAT240032
The science story featured here was enabled by the U.S. National Science Foundation’s ACCESS program, which is supported by National Science Foundation grants #2138259, #2138286, #2138307, #2137603, and #2138296.