where q is the magnitude of the charge bound by a harmonic potential with frequency ω, having a mass µ. The HOMO-LUMO gap of a QDO is ∆E HL = ℏω, which indeed appears in the denominator. However, α can be separately controlled through the other two individual QDO parameters {q, µ}, independently from ∆E HL . This means that for the QDO model, the polarizability and the HOMO-LUMO gap are mutually related, yet they could be tuned separately from each other. The idea of approximating the polarizability using an effective two-state system (so-called Unsøld approximation) is also useful for understanding qualitative trends. Within this approximation, polarizability is written using an average excitation ∆E as a fitting parameter