where σ † n = |e n ⟩⟨g n | and σn = |g n ⟩⟨e n | creates and annilates an excitation on the n th molecule, respectively, with |g n ⟩ and |e n ⟩ as the ground and excited states for molecule n, and ω a is the excitation energy between the molecule's ground and excited state. The corresponding reorganization energy λ is due to exciton-phonon coupling, which is described in the system-bath interaction ĤSB (see Eq. 7).