Axel Becke doesn’t usually wear his medal. He doesn’t even have it on display in his office on the top floor of the chemistry building.
The Dalhousie chemistry professor isn’t even a classically trained chemist. Yet Becke, trained in engineering physics at Queen’s University and theoretical physics at McMaster University, has developed theoretical and computational methods that made a number of discoveries across scientific fields possible.
On Feb. 17, Becke was awarded the Gerhard Herzberg Gold Medal, the highest honour given by the Natural Sciences and Engineering Research Council (NSERC) of Canada. Becke’s area of expertise is “density-functional theory” (DFT). Originally founded in 1964 by Walter Kohn, DFT shows that one needn’t know the individual motions of each electron, but only the overall total density of the electrons, in order to understand and calculate the properties of atoms, molecules and solids.
However, the actual formulas, called functionals, linking the density to the energy and other properties are unknown and need to be approximated. In the late 80s, Becke set out to find approximate functionals accurate enough to be useful in predicting the properties of atoms, molecules and solids.
“For example, calculating bond energies with non-DFT methods is really, really hard,” Becke said. “And what’s more important in chemistry than bond energies?!”
Bond energies measure the strength of attraction between atoms in molecules. They are essential to understanding molecular structures and the energies and mechanisms of chemical reactions.
With Becke’s discoveries in the 80s, DFT began working well and became highly popular. Scientists increasingly used it to understand the chemistry of the systems they were studying.
But in 2004, Becke said he became depressed. He thought DFT was dead.
DFT up to this point was excellent for understanding ordinary bonds, but not more complex interactions such as “van der Waal’s” (vdW) interactions, which are interactions weaker than ordinary bonds. DFT didn’t work for vdW interactions, and these are of paramount importance in biology.
But by 2010, DFT was back in business. Becke and his graduate student, Erin Johnson, figured out how to make DFT work for van der Waal’s interactions, allowing for the application of DFT to biological systems.
A beautiful example of the importance of vdW interactions in biological chemistry—including in the human body—is the structure of DNA. DNA’s double helix configuration is the result of vdW interactions between the nucleobases, causing the structure to twist. If the van der Waal’s interactions are turned off in a DFT computation, the double helix unwinds into a ladder shape.
“Because there were, and still are, problems with it [DFT], I’ve been working on it ever since [the 80s],” he said. “I’m still working on it.”
Now with the award funds Becke has received from NSERC for winning the Herzberg medal, he can bring Johnson from her present position at the University of California to Dal to work on, what he hopes is, the final frontier of DFT: understanding “strong” interactions, which are important in transition metal chemistry and in many chemical reactions.
“For right here, right now, the theory of everything is density-functional theory,” Becke said.
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