The function and properties of materials are determined by the electronic excitation spectrum and we encounter these every day. The best known example is most likely the transparency of glass. By understanding the excitation spectrum, we can understand many of today’s technological developments such as transistors, LED, and photovoltaics.
Microscopic and quantum mechanical effects are fairly well understood today and the excitation spectrum can essentially be calculated. The problem: Existing methods are very complex, requiring a large amount of computing time.
Together with the Theoretical Spectroscopy group at the Ecole Polytechnique in Palaiseau, France, JKU researcher Martin Panholzer (Institute for Theoretical Physics) recently published a paper focusing on an approach to solve the difficult part, the correlations effects, in a model system. The results were then used to calculate a concrete and real material. Dr. Panholzer remarked, “We were surprised that it depends more on the material’s global properties (meaning the average electron density) than the local properties (such as the density at a certain point).”
In other words, in order to calculate the material’s correlation effect, a rough look at the material is enough. The JKU physicist explained, “It’s like wearing the wrong pair of glasses. The electron density appears blurry and you can only determine the average density. We then calculated the correlation effects in this electron soup. We then ‘mixed’ the results with the high resolution density and got very good results.”
This "Time-Dependent Density-Functional Theory" has an additional advantage: researchers can use advanced methods in the model system that are difficult or impossible to realize in the real system. In addition, the correlation effects in different ‘electron soups’ only need to be calculated once. The results are freely accessible and can be used for various materials.
For the next phase, the physicists want to continue pursuing the approach to expand the range of model systems in order to make the methods applicable to certain properties in insulators and semiconductors.
Dr. Martin Panholzer
Institute for Theoretical Physics