Thumbnail image of graphical abstract

The (H2—H2)+ system exhibits a mixed-valence character when the two hydrogen dimers are sufficiently apart, with the hole localized on the dimer with the longest bond. The cover shows energies of the two lowest electronic states (dashed lines) as a function of a reaction coordinate ξ that connects the two ground-state minima. On page 802, Gian Luigi Bendazzoli et al. find that the total position-spread tensor Λ is a powerful indicator of the electron delocalization within the two molecules. A spectacular peak of Λ is found for both the ground and the excited states in the transition state region.