Electronic Properties of Metals and Semiconductors
Large-Scale Electronic-Structure Calculations
The development of advanced 21st century applications increasingly profits from a basic quantum mechanicalunderstanding of material properties. To this end, we have developed a computer code (KKRnano) based on a Green-function formulation of the Korringa-Kohn-Rostoker method which requires computing times that scale linearly with thenumber of atoms in the system  and thus overcome the unfavourable, higher scaling in normal density functionalcalculations.
KKRnano enables us to treat systems with many thousands of atoms with up to more than a million parallel tasks.  Thecalculations can be made very precisely, because the Green function can be determined virtually exactly if non-localangular projection potentials are utilized and if the total-energy functional is evaluated appropriately. 
 A. Thiess, R. Zeller, M. Bolten, P. H. Dederichs, and S. Blügel, Phys. Rev. B 85, 235103 (2012)
 High-Q Club JUQUEEN
 R. Zeller, J. Phys.: Condens. Matter 25, 105505 (2013) and 27, 306301 (2015).
Dilute Magnetic Semiconductors
Semiconductors dilutely doped with magnetic impurities are interesting systems under discussion for spintronic applications.
In a systematic study of the exchange interactions in realistic models of Gd-doped GaN containing nitrogen or oxygen interstitials or Ga vacancies, we found that only Ga vacancies provide a robust path to magnetic percolated clusters which can explain the experimentally observed ferromagnetism with colossal magnetic moments per Gd atom in extremely dilute samples.
 A. Thiess, P. H. Dederichs, R. Zeller, S. Blügel, and W. R. L. Lambrecht, Phys. Rev. B 86, 180401 (2012).
 A. Thiess, S. Blügel, P. H. Dederichs, R. Zeller, and W. R. L. Lambrecht, Phys. Rev. B 92, 104418 (2015).
Phase-change alloys are basic materials in DVD and Blu-Ray technology because of characteristic differences in thephysical properties of their crystalline and amorphous phases. We investigated the role of vacancies on the experimentally observed metal-insulator transition and found that vacancyclusters lead to localized electronic states in the insulating phase.  We also investigated the effects of doping with transition metal atoms and found that ferromagnetic states occur for V andCr doping with Curie temperatures approaching room temperature for large Cr concentrations of 15%. 
 W. Zhang, A. Thiess, P. Zalden, R. Zeller, P. H. Dederichs, J-Y. Raty, M. Wuttig, S. Blügel, and R. Mazzarello, Nat.Mater. 11, 952 (2012).
 T. Fukushima, H. Katayama-Yoshida, K. Sato, H. Fujii, E. Rabel, R. Zeller, P. H. Dederichs, W. Zhang, R. Mazzarello,Phys. Rev. B 90, 144417 (2014).