Simulations on Ohio University’s PSC supercomputer transform coal-like material into amorphous graphite and nanotubes

Coal has gotten some bad press lately. Climate scientists predict that by 2100 the average global temperature will increase by 2 to 10 degrees Fahrenheit. Massive use of carbon-based fuels such as coal is being questioned as weather patterns, crop growth and sea levels can change dramatically.

But it doesn’t have to be.

By powering your car, you can directly reduce your carbon footprint. This shift could also allow us to charge using carbon-neutral energy sources. The kicker is that each Tesla Model S lithium-ion battery requires about 100 pounds of graphite. Scientists have known for generations that, in theory, at least, exposing coal to sufficient pressure and sufficient temperature could transform it into graphite.

To find out how coal is transformed into valuable materials like graphite, David Drabold His physics team at Ohio University decided to simulate matter with computer software. To virtually recreate chemical transformations, they turned to his Bridges-2 advanced research computer at the Pittsburgh Supercomputing Center (PSC). Bridges-2 is PSC’America’s flagship supercomputer funded by the National Science Foundation.

“This road [work] Here are some engineers… doing great work [on carbon-neutral] using coal. I don’t want to burn it for obvious reasons. But can it be made into a high value material like graphite? Nonso and I are very interested in this question. Can graphite be removed from this problem?”

— David Drabold, eminent professor of physics at Ohio University.

Pure graphite is a series of sheets made up of 6 carbon rings. A special kind of chemical bond called an aromatic bond holds these carbons together.

In aromatic bonds, the pi electrons float above and below the ring. These “slippery” electron clouds make the sheets slip easily against each other. Pencil “lead” – a form of lower grade graphite – leaves marks on the paper as the sheets slide off each other and stick to the paper.

Aromatic bonds have another advantage that is important in electronics. Pi electrons move easily from ring to ring and sheet to sheet. This makes graphite, although not a metal, conduct electricity. This is an ideal material for the anode, the positive electrode of a battery.

Coal, by comparison, is chemically nasty. Unlike the strictly two-dimensional nature of graphite sheets, they are connected in three dimensions. It also contains hydrogen, oxygen, nitrogen, sulfur, and other atoms that can interfere with graphite formation.

To begin their research, Drabold’s team created a simplified ‘coal’ consisting only of carbon atoms in random positions. By subjecting this simplified coal to pressure and high temperatures (about 3,000 Kelvin, or about 5,000 Fahrenheit), we were able to take the first steps in studying its conversion to graphite.

“We had to do a lot of serious analysis to extrude the amorphous graphite paper. Compared to other systems we have, Bridges is the fastest and most accurate. Our home system would take about two weeks to simulate 160 atoms, and with Bridges we can process 400 atoms in six to seven days using density functional theory.”

— Chinonso UgmaduPhD student in physics at Ohio University.

First, Ohio scientists performed simulations using basic physical and chemical principles from density functional theory. This accurate but computationally expensive approach required a lot of parallel computation. This is the strength of Bridges-2’s over 30,000 computing cores. They then transferred the calculations to his GAP (Gaussian approximation potential), a new software tool designed by collaborators from the Universities of Cambridge and Oxford, England. GAP uses a form of artificial intelligence called machine learning to perform essentially the same calculations much faster.graduate student Rajendra Tapa And Ugwumadu made the trade-off of leading the initial computational effort.

The result was both more complex and simple than the team expected. A sheet was formed. However, the carbon atoms did not fully develop his simple six-carbon ring. In part of the ring he had five carbons. There were 7 other people.

The non-6-carbon ring provided interesting wrinkles in several respects. The 6-carbon ring is flat, while the 5- and 7-membered carbon rings are wrinkled, meaning the opposite of “positive and negative curvature”. Scientists may have hoped that these wrinkles would ruin the formation of graphite sheets. There is a nature. The sheet was technically amorphous graphite as it is not purely six-ringed. But again, they formed layers.

In another series of simulations, Ugwumadu continued working with Thapa to study molecules rather than solids. These shim conditions caused the seat to curve inward. Instead of sheets, they formed nested amorphous carbon nanotubes (CNTs). That is, a series of monolayer tubes inside another tube. CNTs are of recent interest in materials science because they are effectively tiny wires that can be used to conduct electricity on incredibly small scales. Other promising applications of CNTs include fuel cell catalysis, supercapacitor and lithium-ion battery fabrication, electromagnetic interference shielding, biomedicine, and nano-neuroscience.

One important aspect of CNT research is that Ugwumadu studied how amorphous wrinkles in the tube walls affect the movement of electricity through the structure. In materials science, all “bugs” are also “features”. Engineers may be able to use such irregularities to tune the behavior of certain her CNTs to exactly match the requirements needed for new electronic devices.

The scientists published their results in two papers. On the formation of amorphous graphite sheets in the journal Physical Review Letters June 2022, and About CNTs in Physica Status Solidi B December 2022. Another paper on how five- and seven-membered rings fit into the sheet is published in the European Journal of Glass Science and Technology.

The Ohio team continues to study the conversion of carbon atoms into graphite and related materials. Another ongoing project is the simulation of amorphous nested fullerenes, football-he ball-shaped structures of particular scientific interest in nanoneuroscience. Published a paper on fullerenes The team also explored the possibility of using Bridges-2’s powerful graphics processing unit to speed up ML-based VAST computations, enabling simulations of more complex materials such as real-world coal. allow access.

This article is reprinted with permission of the Pittsburgh Supercomputing Center.