is the relative error. A region of this plot from the lower left to upper right shows relatively constant values of τ below 8 %, which is within the error margins of the quantum dynamics method. This indicates that combinations with either (i) low inclusion and high interface permittivities or (ii) high inclusion and low interface permittivities, reproduced the quantum dynamics permittivity equally well. The induced dipole moment was used as an additional parameter in defining our FEM model. We calculated the optimal fit of the inclusion dipole by partitioning the polarization of the quantum dynamics model using the method described in Sec. 2.5, and determined the relative error of the FEM inclusion dipole (ω) from Eq. 6. This procedure was performed for the 216-atom supercell using data from Hally and Paci to obtain an ω for each tile in the heatmap of Fig. . A pictorial representation, as well as details of the scheme in the quantum dynamics and FEM models are provided in Sec. S5 and Fig. .