A new symmetry underliessearch new materials

A new symmetry underlies the search for new materials

7:29 AM, 19th November 2015
A new symmetry underlies the search for new materials
“Symmetry explains the atomic arrangements and their distortions close to equilibrium.”

UNIVERSITY PARK, US: A new symmetry operation developed by Penn State researchers has the potential to speed up the search for new advanced materials that range from tougher steels to new types of electronic, magnetic, and thermal materials. With further developments, this technique could also impact the field of computational materials design.

“In the physical sciences, making measurements can be time consuming and so you don't want to make unnecessary ones,” said Venkat Gopalan, professor of materials science and engineering. “This is true for any material property - mechanical, electrical, optical, magnetic, thermal or any other. Knowing the symmetry group of a material can greatly reduce the number of measurements you have to make.”

Gopalan gives a simple but scientifically accurate definition. “Symmetry is when doing something looks like doing nothing.”

Symmetry groups tell scientists in how many different ways atoms can arrange in repeating patterns. If they know which symmetry group a material falls into, they already know a great deal about the properties - mechanical, thermal, electrical and so forth – that material will have.

In a paper published online in the journal Nature Communications, Gopalan and his coauthor and former PhD student Brian VanLeeuwen report a new set of boxes called distortion symmetry groups that describes what happens when physical systems are perturbed by stresses, electric and magnetic fields or other forces, and change from one state to another.

“Distortions are the most common phenomenon in nature,” Gopalan said. “A chemical reaction is a distortion, diffusion is a distortion, and a change in the atomic positions and electronic clouds within a material is a distortion. The symmetry that Brian and I discovered is like recording a movie of atoms and looking at its symmetry, whereas most symmetry operations are looking at one frame of a movie.”

VanLeeuwen and Gopalan’s operation is already being applied by colleagues at Penn State working in computational materials design. One group is using the technique to understand and model the diffusion of hydrogen atoms in steel. Another group is incorporating it into a powerful computer code called Quantum Espresso, used by modelers around the globe.

“The first question we like to ask when a new material is discovered is how the atoms are arranged in space,” said Ismaila Dabo, assistant professor of materials science and engineering, and one of the developers of Quantum Espresso. “Symmetries provide a powerful language to explain such atomic arrangements and their distortions close to equilibrium. But when the distortions are so large that they bring the atoms far away from equilibrium, there was no clear way to describe materials transformation, making it difficult to classify critical phenomena like phase transitions or grain boundary motions. This work gives an admirably elegant and much needed answer to that question.”

Proteins are complex crystals that change when a drug molecule attaches to them. But current drug discovery is very computationally and experimentally intensive. Gopalan feels this technique might someday be useful for reducing the number of trials required.

“Biology is all about distortions of bio molecules towards performing a biological function,” he said. “This will be worthwhile knowledge to them. Someday this could be very useful, but biology is highly complex involving hundreds of atoms in a unit cell. We are not yet sure if these ideas could make an impact there, but we plan to try. My goal is to take this and apply it to a variety of simpler problems first.”

© The Pennsylvania State University News

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