Having established SCS-CC2/CBS (3,4) as a reference method for the four excimer models, it is now possible to move on to benchmarking various DFAs. Of the four excimers (Fig. ), benzene is the smallest and has therefore received the most attention in previous computational studies. While the other excimers have received some attention, they are typically studied individually rather than comparatively. The binding of an excimer involves a change in the geometry upon excitation with the eclipsed dimer, also called the "perfect sandwich" structure, widely accepted as the most stable conformation of an excimer. The excitation responsible for excimer formation causes a displaced ground-state dimer to move into this eclipsed form, which is also associated with a reduction in distance between the monomers. The most energetically stable intermolecular separation as determined experimentally for aromatic excimers is reported in the range of 3.0-3.6 Å. Our SCS-CC2/CBS(3,4) r e values, reported in Table , fall within 0.03 Å of this range which is reasonable given highaccuracy theoretical calculations tend to predict shorter r e . The close and parallel stacking of the eclipsed formation facilitates excimer binding interactions: electrostatics, Pauli-repulsion, CT, exciton coupling and London dispersion. For example, parallel stacking and short intermolecular distance increases orbital overlap, promoting exciton delocalisation. The interplay of these various interactions may present a challenge for DFT methods to properly describe the dissociation energies and intermolecular distances. The main focus of this section is to investigate DFAs with this in mind. Before we discuss each model system individually, we study the impact of the amount of FE on the TD-DFT dissociation energies. Each model system is then first discussed without the addition of dispersion corrections before the impact of said corrections is studied separately. This section ends with an overarching discussion across all four dimers by means of statistical analysis.