When the diameter is less than 8 nm, both ab initio and ωFQ deviate from the BEM continuum curve; in particular, a large blueshift arises, which is almost 0.2 eV for D = 2 nm at the ωFQ level. However, for such small structures, the reference ab initio results do not present a clear trend as a function of the disk diameter, thus probably showing that the molecular limit is reached. 23 As a consequence, ωFQ cannot exactly reproduce the ab initio trend because the Drude model may fail in the limit of molecular excitations which are ruled by quantum mechanics. 23 , 39 In Figure 3 c, ωF
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