In periodic systems plane-wave basis functions are often used. In a previous question on this site it was questioned if plane-wave basis-sets are reliable for modeling adsorption-processes

The answer to that question was ultimately "yes" they are good and appropriate for adsorption process.

However, Gaussian based wavefunction theories are still far ahead of plane-wave theories in key areas like excited-states. For example, it is not possible, as far as I know, to do plane-wave based "configuration interaction" calculations.

Accurately calculating excited-states is important because molecular crystals have much different photonic properties. For example, molecular crystals can display aggregation induced emission, increased oscillator strengths and emission wavelength shifts. All very relevant and impossible to capture with the single molecule.

Therefore, what are some of the methods to model excited-states in molecular crystals?