Where Γ(∞) is bulk damping frequency, vF (cm/s) the Fermi velocity
and A is a model-dependent parameter. For the determination of
this parameter Γ(R), we need to adjust the radius R (nm). The use of
the Maxwell-Garnett theory is appropriate to the evaluation of the
absorption due to a population of NPs embedded in a medium, thus
we can evaluate αSPR(ω) knowing the effective dielectric constant
εeff and the fill factor f lower than fAg or fCu [32]: