HEDS Fellow John Copley’s modeling methodology

John Copley is the newest High Energy Density Science (HEDS) Center fellow at Lawrence Livermore. This fellowship provides him with the opportunity to independently pursue research related to the study of matter and energy in extreme conditions. In Copley’s case, this involves developing improved methods for modeling material phase transformations and equilibria at high pressures, a refreshing change from his background in experimental research.

Unusually for materials scientists, Copley knew that he wanted to pursue a career in the field since high school after being wooed by graphene—a single-atom-thick layer of carbon and the world’s thinnest, strongest and most conductive material—and finding himself interested in material behavior at the atomic level. “I always liked understanding how things worked, and materials science was great avenue to explore that fundamentally,” he said. “In order to do materials science, I would need a Ph.D., so I knew before undergrad that I was going to get a Ph.D. in materials science.”

Copley stuck to the plan, first attending the Colorado School of Mines for his undergraduate and master’s degrees. He completed his master’s in the Metallurgical and Materials Engineering Program studying high-entropy alloys (that is, alloys made of several principal elements in relatively similar amounts), observing their behavior when they were deformed or compressed quickly. His work in this area sought tough materials that would perform well in armor or crumple zones of cars.

A New Frontier

After completing his degrees in Colorado, Copley became a Stewardship Science Graduate Fellow (SSGF) and pursued a Ph.D. at Princeton University. For this degree, his work used diamond anvil cells to study iron and cadmium selenide’s phase transitions and kinetics. The SSGF program includes a required practicum students must undertake at Lawrence Livermore, Sandia, or Los Alamos national laboratories. This practicum, which encourages students to branch out into something different from their main research, is what first brough Copley to Livermore and started him on the computational research path.

“Everything I had done for my master’s and Ph.D. had all been experimental,” Copley said. “I wanted to do something computational for my practicum for two reasons. One is that there is something satisfying about experiments, but they can be frustrating with time constraints and long hours. The other is that so many papers these days are computational, and I really didn't have any experience with it, so I wanted to learn more about why people make the computational choices that they make.”

Livermore’s computational resources and diamond anvil cell research expertise made it just the place for Copley to take on this endeavor, which he did in fall of 2023. For his practicum, he developed a computational method to examine material melting using hybrid Monte Carlo molecular dynamics methods. With molecular dynamics, one simply observes what happens to a system according to Newton’s laws of motion. The Monte Carlo aspect enabled Copley to introduce hypothetical, physically impossible phenomena to the system and observe their response. These phenomena were mostly swaps of the locations of two atoms in the system. By implementing these swaps, he could simulate changes in solid systems which would otherwise produce very minimal change over time, and these systems could thereby offer up more information about their thermodynamic equilibrium.

This project would not be the end of Copley’s computational work. “After my practicum, I realized that what I like doing in science is method development, and I am less invested in the specific materials I work on,” he said. “I'm really interested in developing new techniques, and there was a limitation in the technique that I'd done with my practicum, which was that the atoms in the systems I looked at had to be pretty similar.” He had studied the similar elements copper and nickel, as well as iron and nickel due to their geoplanetary applications as main components of the Earth’s core. Swapping the positions of non-similar atoms, like one carbon and one iron atom, is impossible due to the differences in space that the atoms fill—necessitating development of a new way of simulating mixing in the system.

Finding a Solution

For his HEDS Center fellowship application, Copley proposed to develop Monte Carlo moves that work differently from the direct swaps that he had been using before. Instead, his simulations would find intelligent places to move carbon atoms within the system such that they are compatible with nearby atoms.

He had some ideas about how to make this happen, and Livermore’s existing expertise served as the perfect grounds for collaboration on the problem. “As it turns out, when I arrived back at the Lab, Flynn Walsh had written a code that looked at proposing moves of atoms to create more accurate structures of things like grain boundaries,” said Copley. “But that code could also be modified to enable intelligently finding a good location for the carbon atoms.”

The two modified the code for Copley’s applications, and they are now working with Sebastien Hamel to apply the concept to iron/carbon systems at 300 gigapascals of pressure—conditions like those at the center of the Earth. Copley hopes to move on to modeling the behavior of more complicated systems once the code for iron and carbon is finalized, with applications for engineered materials and more.

His time at Livermore has served Copley well so far, and when he’s not busy developing new computational research methods, he also enjoys spending his time talking to his wife back in New Jersey and exploring the methodology of baking and cooking. “The Lab is a place where I have access to computational tools that are unrivalled, and I can collaborate with people doing some of the only experiments that match with the computational work that I’m doing,” he said. “My work is both challenging and fun in that there is always room to improve my methods, which is fostered by Livermore’s collaborative environment.”

—Lilly Ackerman