Complex computer simulations can shed some light on new material properties. Professor Karsten Held from the Vienna University of Technology is developing new numerical methods to calculate and understand the subtle quantum mechanical interplay between the electrons which is responsible for a multitude of interesting effects. The European Research Council (ERC) has now awarded him an ERC Starting Grant of approximately 1.5 million Euros. With this grant, Held is going to extend his research group and intensify his scientific work in the next five years.

Many Particles – Complex Calculations

The first object ever to be described by quantum mechanics was the hydrogen atom – a particularly simple system with only one electron. Each additional particle which has to be taken into account makes the calculations much more complicated. Still, there are ways to accurately describe the interactions between large numbers of particles.

For materials science, this is crucially important. Many interesting properties of newly developed materials can only be understood if the quantum behavior of the electrons is simulated on a computer. “High temperature superconductivity, quantum phase transitions close to zero temperature or the behavior of electrons in tiny nanostructures – there are many quantum phenomena, which are still not sufficiently well understood”, says Karsten Held.

The Nobel Prize was Just the Beginning

A major step forward was made in theoretical materials science by density functional theory, for which the Nobel Prize in Chemistry was awarded to Walter Kohn in 1998. Over the last few decades, there have been many important developments in the quantum theory of solid materials. Only a few years ago, the “Dynamical Mean Field Theory” (DMFT) was developed. Karsten Held is considered to be one of its pioneers.

The DMFT-method can describe the quantum correlations between electrons sitting at one lattice point of the crystal. For many important effects, however, the correlations between electrons at different lattice sites has to be taken into account. “DMFT was a big step forward, and today it is state of the art, but especially at low temperatures, there are effects which cannot be explained by this model”, says Karsten Held.

Therefore, Karsten Held and his team are working on a new method – the “Ab Initio Dynamical Vertex Approximation” (DGA), which also describes electron correlations on larger length scales. This became possible by applying mathematically challenging concepts from quantum field theory. “First tests have shown that our method works. Now we want to develop it further. We will use it to understand important physical phenomena and to simulate specific materials on the computer”, says Held.

Fundamental Research and Applied Science

On the one hand, the new method is supposed to help understand new materials and to come up with new insights into superconductivity, quantum phase transitions and nanostructures. One the other hand, it should also help to obtain a deeper theoretical understanding of these phenomena.

The ERC grant gives Karsten Held the opportunity to enlarge his team and to establish one of the world’s leading groups in this area. The available computer infrastructure is going to play an important part in this project - extraordinarily complex calculations require extraordinary computing power, which will be provided by the mainframe computer VSC at the Vienna University of Technology. Karsten Held is optimistic: “Vienna has a long tradition of developing computing methods in solid state physics. We want to continue this tradition and develop numerical methods for the 21st century.”

Professor Karsten Held grew up in Germany. He studied at RWTH Aachen and did his PhD at Augsburg University. He got a postdoc position at Princeton University (USA), then he returned to Germany and became the head of the Emmy-Noether-group at the Max Planck Institute for Solid State Research in Stuttgart. In 2008 he was appointed professor at the Vienna University of Technology.

https://www.ifp.tuwien.ac.at/forschung/projekte/erc-abinitiodga//, opens an external URL in a new window 

Contact

Univ. Prof. Karsten Held
Institute of Solid State Physics
TU Wien
Wiedner Hauptstraße 8
1040 Vienna
Phone: +43 1 58801 13710
Email: karsten.held@tuwien.ac.at