Time-dependent DFT in CASTEP has been available for a while; the recent paper by an international team that includes CASTEP developers shows an effective application of this technique to modeling of fluorescence spectra from organic co-crystals, see https://pubs.acs.org/doi/10.1021/acs.jpca.8b03481 .

This is the first demonstration of a periodic ab initio prediction of solid-state fluorescence spectra of organic crystalline materials. Interpretation of results shows that the stacking has a major effect on spectra, hence it would be very difficult to reproduce it in a "standard" cluster calculation. This example application can be used to build a strategy for efficient theory-driven design of novel luminescent materials.

Victor Milman, BIOVIA Science Council