Cluster 3.1 exhibits the largest binding energy and turns out to be the most stable geometry in the S1 state. As already observed with both TD-DFT and higher-level methods, the computed values tend to overestimate the experimental ones. Several factors contribute to this discrepancy, starting with the different definitions of the quantity, which is often extrapolated experimentally from the difference between pyrene absorption and excimer emission energies. The latter approach may incorporate ground-state repulsion within a given excimer conformation.