The pyrene excimer is considerably more stable than the benzene excimer with a reference D e of 33.29 kcal/mol at r e = 3.19 Å (Figure ). Here, almost all TD-DHDFs underbind the pyrene excimer, though overbinding is exhibited by ωPBEPP86 [Figure (e)] and ωB88PP86 (Figure ) for reasons explained earlier. Absolute deviations in D e range from 1.43 [ωB88PP86] to 19.21 [SOS-B2PLYP] kcal/mol (4 to 58% errors) and in r e range from 0.01 to 0.26 Å. Compared to the benzene excimer, the larger system size results in larger deviations in D e , suggesting the greater role of dispersion for the pyrene excimer may result in larger deviations from the reference due to the methods' inability to inherently accurately describe dispersion interactions.