Featured Lendület Researcher: Gábor Czakó

Chemistry has traditionally been an experimental science, but in recent decades the theoretical approach has been gaining ground within chemistry. Nowadays, chemical reactions can not only be studied experimentally, but theoretical chemists can use the laws of physics and the tools of mathematics and computer science to calculate the precise mechanisms by which these reactions take place. This is the work of the Momentum research group led by Gábor Czakó at the University of Szeged.

Detailed description of real events

“Our research group, the Theoretical Reaction Dynamics Research Group, investigates chemical reactions, and more specifically, how these reactions take place at the atomic and molecular level,” says Czakó. “I’ve always been involved in theoretical chemistry, since my Master’s degree. After my PhD, I was a postdoctoral researcher at Emory University in Atlanta from 2008 to 2011, where I started the reaction dynamics studies that led to this Momentum grant.”

Gábor Czakó

After returning home, the chemist continued this research, first at ELTE and then, from 2015, at the University of Szeged, where he founded his first research group. They first won a grant from the Momentum programme in 2019, and this year they have now been awarded an advanced grant. “So, with the support of Momentum, we have been working on this topic for five years now, but our research goes back fifteen years,” continued the research team leader.

Atoms and molecules are involved in chemical processes, but understanding the motion of the electrons and nuclei that make up atoms is essential to arrive at a detailed description of what is actually happening. The first step is to describe the movement of electrons, from which we can determine the potential energy surface. These surfaces play a key role in describing the motion of nuclei.

“One of the keys to our research work is that we can calculate these surfaces point by point and fit a mathematical function to them.”

Quantum simulations of reactions

The main achievement of the first Momentum project was the development of software that can automatically construct potential energy surfaces. This allowed the researchers to significantly improve the efficiency of reaction dynamics studies. Now, in the second project, the main goal is to be able to handle the motion of nuclei using the laws of quantum mechanics. So far, the motion of nuclei has been described by classical Newtonian mechanics, which provides a fairly good description of the reactions, since atomic nuclei are significantly heavier than electrons. But in order to execute even more accurate and realistic simulations, it is also important to take quantum mechanical effects into account, especially when, for example, low-mass hydrogen atoms are involved in the reaction.

“Our main goal is to perform quantum simulations on the reactions and develop models that are currently not available in the literature,” says Czakó. “But we also have experimental collaborators. While we are investigating how these reactions take place in a purely theoretical way, the same systems can also be studied under laboratory conditions. That’s why we are working with an experimental group at the University of Innsbruck, for example, who are at the forefront of this type of measurement.”

They compare the computational results with the experiment, which is useful from both a theoretical and experimental point of view. Sometimes it turns out that the calculations provide a deeper insight into the reactions than the measurements. The reason for this is that, experimentally, they can often only detect products, and sometimes not even all products (detecting products without a charge is often very difficult). In contrast, theoretical chemists can use their calculations to more easily identify all the products, while also seeing the reaction pathway through which the transformation occurs. “Theoretical chemistry has now reached the point where it can not only reproduce experimental results, but also make realistic predictions. Theory is often necessary to explain experimental results, and the information it provides complements the measurements.”

Czakó said that nowadays it is often the case that if theory and experiment do not give the same results, then it is more a problem with the measurements (since all measurements have uncertainties and the experimental method can also have errors). They have seen examples of this in their own research. Their previous studies have produced a number of significant results, as shown by the fact that they have published three papers in the last nine years in Nature Chemistry, which is considered the world’s leading chemistry journal. “This suggests that our work has attracted the interest not only of theoretical chemists, but also of a wider audience of chemists.”

The theoretical chemistry approach can now be used to simulate any material system, from the smallest reactions to large biomolecules. The accuracy of the calculation is inversely proportional to the size of the system, so greater reliability can be achieved with small systems, while larger ones have higher inaccuracies. For theoretical chemists, even the simplest reactions can hold surprises, so there are research groups around the world that study the smallest reactions, such as the reaction of a hydrogen atom with a hydrogen molecule. At the same time, there are also researchers working on macromolecules.

Exploring the fundamental laws of chemistry

The Momentum group is currently investigating a few (5-12) atomic systems, but their aim is to extend the scope of their accurate simulations to larger reactions. “We usually study fundamental organic reactions, such as the reactions of methane and other small hydrocarbons, or reactions of small organic molecules containing a heteroatom with different atoms,” says Czakó. “We also study ion-molecule reactions. Of particular importance among these is the S_N2 reaction, or bimolecular nucleophilic substitution, a fundamental reaction in organic chemistry. We play a pioneering role in the dynamic investigation of S_N2 reactions, as we were the first to develop high-precision potential energy surfaces for these reactions.”

The mechanism of S_N2 reactions has been known for more than a hundred years, but what happens at the atomic level still holds many new discoveries and surprises. The research group has already found several new reaction pathways for S_N2 reactions. “Our main goal is to uncover fundamental laws of chemistry that may prove generalisable and can be applied to larger systems,” argues the team leader.

“We want to understand how reactions occur and why they occur the way they do.

If we can understand this, we may be able to direct the processes towards products that are more favourable to us.”