Therefore, a continuum model must account for both the electronic coupling to the Ag inclusion and the increased ionic polarizability of the ions nearest the inclusion. To capture this coupling, we include an explicit interfacial layer, which is also ellipsoidal in shape, but with its axes all increased by a fixed thickness relative to the inclusion. This interface is assigned its own permittivity different than that of the bulk matrix by fitting the continuum model to quantum dynamics results as detailed in the following section. As expected, the best fit model includes a high-permittivity interface.