Tech: 'Fudge Factors' in Physics? Team says it's time to restart – (Report)

The field of quantum physics, with its complex mathematical equations to predict the interactions and energy levels of atoms and electrons, has already made possible many of the technologies we rely on every day – from computers to smartphones, lasers to magnetic resonance imaging. And experts say that revolutionary advances are destined to come.

But to take a giant step, you have to be in good physical shape, and researchers at the University of Delaware have discovered a field of quantum physics that could use more callisthenia, you might say. The research, conducted by PhD student Muhammed Shahbaz with his advisor, Professor Krzysztof Szalewicz from UD's Department of Physics and Astronomy, was recently published in Letters of physical examination, the journal of the American Physical Society.

Like people, atoms can be attracted to one another or, well, pushed back. Take argon – the third most abundant gas in the Earth's atmosphere. This non-reactive gas has a variety of uses, ranging from historic document protection to corrosion prevention of tungsten filament in fluorescent lamps. When two argon atoms are moved away from each other, they will be attracted to each other until they reach 3.5 angstroms before repelling each other. one and the other. It's as if, once they've looked really good, they're ready to move on.

But this is not what physicists discovered about two decades ago by testing the density functional theory (DFT), which is now widely used to model and predict the electronic structure of atoms. Most versions of DFT predicted no attraction or were only very weak. Where is the failure? The attraction between the argon atoms stems from the "scattering interactions" between the electrons because the motions of an atom's electrons influence the motions of its partner's electrons. DFT can not accurately account for these correlated long-range motions.

And this is a problem, especially in a field like materials science, where physicists can design and predict the properties of a new material – from its strength to its magnetic power – to its ability to drive heat – without never go to a laboratory to do an experiment.

Physicists therefore began to develop "fudge factors" in the early 2000s to take into account this dispersal energy. Some of these methods have proven relatively satisfactory and have become an extremely popular tool in computer physics, chemistry and materials science. Scientific articles proposing such methods have been cited tens of thousands of times.

What Shahbaz and Szalewicz have shown, after more than a year of intense analysis, is that all these dummy methods are actually based on an erroneous assumption. The DFT can describe how the motion of an electron affects and is affected by the motion of another electron when the distance between them is in the order of the angstrom. For separations greater than one angstrom to about seven angstroms, the correction methods assume that the DFT recovers a fraction of these effects. Shahbaz and Szalewicz found that this amount did not have the characteristic properties of dispersion energy and actually came from theoretical errors not related to dispersion. Thus, say the researchers, correction methods can give good results, but for the wrong reasons.

"We are telling the physics community that we need to go further and adopt a universal prediction method that works for the right reasons," says Shahbaz. "We are not here to criticize, but to help improve," he adds humbly.

Szalewicz and Shahbaz are currently part of a team of theoreticians and experimenters from American universities who use quantum physics to predict crystal structures and energies, including snowflakes, ice, most rocks and minerals, some plastics, pharmaceuticals. , energy equipment and other products are manufactured. Their complex calculations predict, for example, how much energy can be stored in a given volume of rocket fuel.

Shahbaz, who is the first author of the newspaper article, claims that he would never have imagined a child in his small village of Pakistan that he would one day become a professor of physics. He grew up helping his father, a farmer, grow reeds, rice, pepper, tomatoes, eggplants, radishes and okra. He is now the first member of his family to obtain a university degree – not to mention the highest university degree, which is now clearly visible.

When he applied for graduate studies, he received offers from American and Canadian universities, but finally decided to choose UD because of the University's reputation and the flexibility it had to start mastering. He says it helped him decide what he really wanted to focus on.

When he finishes his doctorate in the coming months, he already has a job as an assistant professor of physics at Punjab University in Lahore, where he is intended to entice students to understand how the light works and of gravity, just as he was fascinated in his youth.

So why does he like physics so much?

"Physics tells you about the laws of nature," says Shahbaz. "It also requires reasoning. You do not have to memorize anything, simply absorb life. "

This work was funded by the US Army Research Laboratory, the Army Research Office, and the National Science Foundation.