(5) where n is the refractive index of the surrounding medium (taken to be water, with n = 1.33, throughout); an analogous expression defines the interaction potential operator for the acceptor. This treatment is similar to that employed in the hybrid CQED/ab initio electronic structure model of plasmon-molecule interactions described in Ref. 21. The potential defined in Equation ( ) is a point dipole approximation to the interaction between the donor and the acceptor, which may break down when the length-scale of separation between the donor and acceptor is similar to the length-scale of the donor/acceptor itself, or when there are higher multipolar contributions to the charge density oscillations that drive the interaction; 3,48 both limitations to the point-dipole approximation may be important in the systems studied herein. An approach to the interaction potential that overcomes these limitations is provided by the transition density cube method, which provides the full Coulombic interaction between the charge density oscillations on donor and acceptor species to within the accuracy of the level of theory used to compute the many-electron wavefunction of the donor and acceptor. However, calculation of the requisite many-electron wavefunction for nanoparticles, even at low levels of theory, represents a considerable computational challenge and is beyond the scope of this work.