All calculations were performed using the ωb97x density functional and the 6-31+G* basis set to be fully consistent with the QM/MM dynamics. This was done to avoid well-known issues in the computation of spectral densities that arise from a mismatch between the Hamiltonian used to propagate the system and the Hamiltonian used to compute vertical excitations. The effect of DFT functional choice in both QM/MM dynamics and vertical excitation energies on resulting optical spectra was analyzed in detail, with results reported in SI Sec. 5.