The computer simulation of complex systems often requires approaches which cover very different
length-scales as in describing a photo-active chromophore embedded in a large protein or a solvated
molecule. To this aim, one often employs hybrid multi-scale methods where a more accurate description
is adopted for the active site and a coarser one for the rest of the system.
In this context, embedding potentials are frequently used to account for the effect of an environment on
the electronic structure of molecules in larger systems, including their excited states.
If the excitation is accompanied by significant rearrangements in the electron density of the embedded
molecule, the environment is expected to strongly respond to this perturbation. Furthermore, non-classical
interactions may play a significant role.