The Seamless Connection of Local and Collective Excited States in Subsystem Time-Dependent Density Functional Theory

The theoretical understanding
of photoinduced processes in multichromophoric
systems requires, as an essential ingredient, the possibility of accurately
describing their electronically excited states. However, the size
of these systems often prohibits the usage of conventional electronic-structure
methods, so that often multiscale approaches based on phenomenologically
motivated models are employed. In contrast, subsystem time-dependent
density functional theory (sTDDFT) allows for a subsystem-based ab initio description of multichromophoric systems and therefore
allows for, in principle, an exact description of photoinduced processes.
This Perspective aims to outline the theoretical foundations and commonly
used practical realizations as well as to illustrate benefits of recent
developments and open issues in the field of sTDDFT. Prospective,
potential future applications and possible methodological developments
are discussed.