Figure 1: Selected Sn⁺_N structural isomers stressing the quasi–spherical–to–prolate transition observed for this size regime. Relative energies in eV on the PBE0/cc-pVTZ-PP level of theory are given in bold letters, while LC-ωPBEh/def2-TZVPP results are shown in parantheses. The simulated optical spectra showing the absorption cross section σ as a function of the photon energy ћω are given for the Sn⁺₁₃ isomers, with isomer 13-II stating a stabilized icosahedral configuration with unusualy intense and discrete electronic transitions.