Thursday , June 24 2021

Supercomputers help with the study of two-dimensional materials



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IMAGE: This is an atomic model illustrating multilayer lithium atoms between two graphite sheets.
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Regards: Dr. Mahdi Gorbani-Asl, HRDD. See M. Kühne, et al., Nature 564 (2018).

Whether high-temperature superconductors and improved energy storage for folding metals and tissues capable of completely blurring fluids, material scientists study and understand the physics of interacting atoms in solids to find ways to improve the materials we use in every aspect of everyday life.

The boundary of material science research, however, is not in alchemical experiments and errors; for a better understanding and improvement of materials today, researchers should be able to study the properties of materials at the atomic scale and under extreme conditions. As a result, researchers increasingly rely on simulations to complement or inform experiments on the properties and behavior of materials.

A team of researchers led by Dr. Arkady Krasheinnikov, a physicist at Helmholtz-Zentrum Dresden-Rossendorf, partners with experimentation to answer fundamental questions about material properties, and the team recently had a big breakthrough – experimentalists were able to observe in real time behavior of lithium atoms when placed between two graft leaves. Graffen sheet is what researchers consider to be a 2D material, since it is only one atom thick, making it possible to monitor lithium atom movement in transmission electron microscopy (TEM) experiments.

With access to supercomputer resources through Gauss's GCS, Krasheninnikov's team managed to use Hazel Hen supercomputer for high-quality computing centers in Stuttgart to simulate, confirm, and expand the team's experimental results. Joint work has recently been published nature,

"2D materials have useful and exciting properties and can be used for many different applications, not just as support in TEM," says Krasheinnikov. "Essentially, 2D materials are at the top of the material research, probably about two thousand such materials and about 50 are made."

Under the microscope

To better understand experimental 2D materials, scientists routinely use TEM today. The method allows researchers to suspend small, thin pieces of material, then release a high-energy electron beam over it, ultimately creating an increased image of the material scientists can learn, like a movie projector that takes image from a drum and projects. on a larger screen. With this view in the material, experimenters can better plot and evaluate the positions and arrangements of the atoms.

The high-energy beam can do more than help researchers to observe the materials, but it is also a tool for exploring the electronic properties of 2D materials. In addition, researchers can use high-energy TEMs to kill individual atoms of high-precision material to see how material behavior changes based on structural change.

Recently, Max Planck, Stuttgart, and Ulm University's experimental investigators wanted to better understand how lithium particles interact between two thin-film graphite sheets. Better understanding of lithium intercalation or lithium between layers of other material (in this case graphene) helps researchers develop new methods to develop better battery technologies. Experimentalists received TEM data and asked Krasheinnikov and his associates to rationalize the experiment with simulation.

Simulations allow researchers to see the atomic structure of the material from different angles, and they can also help to accelerate the approach to experimentation and error in the design of new materials by experiment only. "The simulations can not do the whole thing, but they can really limit the number of options and show the direction to go," Krasheninnikov says. "Simulations save money for people working in the field of fundamental research and industry, and as a result, computer modeling is becoming more and more popular."

In this case, Krasheninnikov and his collaborators found that the atomic coordinates of the experimenters or the particle positions in the material would not be stable, which means that the material will oppose the laws of quantum mechanics. Using data from the simulation, Krasheninnikov and his collaborators offered a different atomic structure and when the team rethinked their experiment, it found a perfect coincidence with the simulation.

"Sometimes you really do not need a high-level theory to understand the atomic structure based on experimental results, but sometimes it's impossible to understand the structure without precise computational approaches that go hand in hand with the experiment," Krasheinnikov says.

Experimentalists were able, for the first time, to observe in real time how lithium atoms behave when placed between two graphene sheets, and with the help of simulations, they get an idea of ​​how the atoms are arranged. It was previously assumed that in such an arrangement lithium would be structured as a single atomic layer, but the simulation showed that lithium could form bi- or trilayer, at least in the two-layer graphite, which led researchers to look for new ways to improve battery performance.

Loading ahead

Kraseninnikov noted that while the simulation has made great strides over the past decade, there is still room for improvement. The team can efficiently perform first-order simulations of 1000-atom systems over time to monitor short-term (nanoseconds) time-based material interactions. The larger number of next-generation supercomputer cores will allow researchers to include more atoms in their simulations, meaning that they can model more realistic and significant parts of the material in question.

The greater challenge, according to Kraseninnikov, is related to how long scientists can simulate material interactions. To investigate phenomena that happen over longer periods of time, such as how stress can be formed and spread a crack in metal, scientists need to be able to simulate minutes or even hours to see how materials change . However, researchers also have to take extremely small time steps in their simulations to accurately model super-fast atomic interactions. Simple use of multiple computational nuclei allows researchers to make calculations for larger systems faster but can not make faster steps in time if a threshold of "parallelization" is reached.

Violation of this closure will require researchers to process algorithms to calculate more efficiently each step through the large amount of nuclei. Kraseninnikov also pointed out that quantum-based code-design can allow simulations capable of monitoring material phenomena occurring for longer periods of time – quantum computers – to be ideal for simulating quantum phenomena. team can not do good research without good computer resources, "he said.

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