The pyrene excimer (Fig. ) is more stable than the anthracene excimer, with an SCS-CC2/CBS(3,4) dissociation energy of 36.33 kcal/mol at 3.19 Å. Similarly to the naphthalene dimer, we also observed the wrong order of states at the dissociation limit for some functionals, something that can be avoided when using symmetry in the calculation.