where ω p is the plasma frequency, γ is the damping coefficient, ε ∞ is the high-frequency permittivity, and ε 0 is the vacuum permittivity, and the permittivity of the background medium ε m is assumed real and frequency-independent over the range of interest. The patches and linkers are ignored in the optical calculations. We set γ = 0.05ω * p and ε ∞ = 2ε m , where ω * p = ω p ε 0 /ε m is an effective plasma frequency. For generality, extinction spectra are shown in terms of a dimensionless extinction cross-section per nanoparticle volume