Recent Research Highlights:
1. Exciton binding energies in semiconductors and insulators
In another recent paper we showed that hybrid approaches such as screened exact exchange (SXX) are a promising (and cheaper) alternative to the BSE: Zeng-hui Yang, F. Sottile, and C.A. Ullrich, Phys. Rev. B 92, 035202 (2015).
Yonghui Li and C. A. Ullrich, J. Chem. Phys. 145, 164107 (2016)
3. Spin waves in chiral electron gases: interplay of spin-orbit coupling and electronic many-body effects
As a follow-up study, we did a careful analysis of the dependence of the spin-wave dispersions on the direction of propagation. We found that our TDDFT calculations reproduce the angular modulation very well, see S. Karimi, F. Baboux, F. Perez, C. A. Ullrich, G. Karczewski, and T. Wojtowicz, Phys. Rev. B 96, 045301 (2017).
TDDFT is not the only DFT-based method to calculate excitation energies. Going back to the work by Oliveira, Gross and Kohn in 1988, another formally exact approach is based on ensembles of excited states. However, at present the ensemble-DFT approach has not been very widely used, since it lacks the accuracy and convenience of TDDFT. But there has been a lot of activity in recent years in the field of ensemble-DFT for excited states, and much progress has been made.
We have recently found a way to directly extract electronic excitation energies based on ensemble-DFT, see Zeng-hui Yang, Aurora Pribram-Jones, Kieron Burke, and C. A. Ullrich, Phys. Rev. Lett. 119, 033003 (2017). The approach is computationally cheap, and its accuracy is comparable to that of TDDFT. An additional great advantage is that it yields double excitations without any additional effort (in contrast with standard TDDFT), as shown here for the example of the beryllium atom, see the picture above. However, much work remains to be done: in particular, we need better exchange-correlation functionals for ensembles.