A new approach in quantum chemistry

What happens if interactions between electrons are actually enormously strong?

paoli-giori‘Van der Waals forces’ are the natural forces that make water droplets cling to glass and peanut butter stick to your sandwich. As commonplace as these forces are, we are still unable to calculate them precisely. The theoretical chemist Paola Gori-Giorgi is foraying into quantum mechanics, with a new idea.

Quantum mechanics
“I do research into quantum chemistry – developing methods to calculate molecules, really,” says Gori-Giorgi, professor of Theoretical and Mathematical Chemistry at Vrije Universiteit Amsterdam. Quantum mechanics is chemistry at the smallest possible scale: atoms and electrons. In principle it enables the calculation of how electrons behave in atoms, and bind molecules. The famous physicist Paul Dirac called this ‘the end of chemistry’, because in theory you would never need to enter a chemical laboratory again. “But there’s a problem, of course: if the molecule is bigger than a couple of atoms, precise calculations may take longer to carry out than the age of the universe. So we have to approximate.”

The quantum chemistry calculation method most often used is Density Functional Theory, or DFT. Gori-Giorgi: “This usually works very well, and quickly, but there are situations where it does not: if the interactions between the electrons in a molecule play an important role, for instance, and also in Van der Waals forces.” Van der Waals forces exist between different molecules; for instance, they make a drop of water cling to a glass.

“I’m trying a new approach in quantum chemistry,” says Gori-Giorgi. “Using DFT, normally you assume a system with no interactions between the electrons: the electrons do not feel each other’s presence. You then use that non-physical situation as the basis for your calculations. But I’m asking: what happens if those interactions are actually enormously strong? If the electrons repel one another extremely strongly? This isn’t realistic either, but you can use these two complementary limits to say something about real molecules, that lie somewhere between these limits.”

The VICI research grant that Gori-Giorgi was awarded was for the analysis of Van der Waals forces using the same approach. “I was at a conference, discussing it with a well-known mathematical physicist, and he showed me a sketch of electrons in Van der Waals correlation. I thought: hey, I’m seeing the same thing happening in my own approach. It all suddenly fell into place. I pretty much ran off to write my VICI proposal.”

There certainly are applications for quantum chemistry, says Gori-Giorgi. “But to be honest, I’m not all that interested in specific applications, such as medicines. Still, every time I develop something new, I notice that other researchers ask me to collaborate with them. That’s what I like about science: it’s a collective enterprise. Everyone has their own field of expertise. Mine is all about the fundamentals, and the issues of importance there; other people go on to use that knowledge.” An example is the VU spin-off company Software for Chemistry & Materials (SCM). SCM offers state-of-the-art software packages for performing quantum chemical calculations, and their clients include large pharmaceutical and chemical companies. Gori-Giorgi: “If my approach works, then sooner or later it’ll be included in those packages.”