To further quantify how strongly the nuclear degrees of freedom of the chromophore and solvent couple to the electronic transition, we integrated the spectral density to produce the reorganization energy, λ, as given in Eq. 5, and partitioned it into the contributions from the low-and high-frequency regions of the spectral density: the low-frequency reorganization energy, λ LF , was computed by integrating J LF (ω) (Eq. 6), and the highfrequency contribution, λ HF , was simply taken as the difference between λ and λ LF . As shown in the top part of Table , QUBEKit (0.011 eV) significantly underestimates λ LF compared to that from QM/MM (0.040 eV), whereas revQUBEKit (0.030 eV) improves the agreement substantially, consistent with our observation of the lowfrequency region of the spectral density (Fig. ). The axial H-bonding in the revQUBEKit simulation is primarily responsible for this enhancement. In contrast, the higher intensities above 600 cm -1 in the spectral densities from QUBEKit and revQUBEKit (Fig. ) lead to larger λ HF values than that from QM/MM. As discussed later, the QM/MM chromophore-solvent model may underestimate the coupling between the electronic transition and the high-frequency chromophore vibrational modes due to closer peripheral H-bonding solvent, leading to less intense peaks in the high-frequency region of the spectral density. The total reorganization energies λ, from the force fields are the net result of the lower λ LF and the higher λ HF compared to the respective values from QM/MM. With the Condon approximation and the second-order cumulant truncation, the absorption spectrum depends solely on the spectral density (Eq. 3). We present the resulting spectra in Figure , with all spectra aligned energetically with the absorption maxima for better comparison of spectral shapes, see SI, section S8 for unaligned spectra and values for applied energy shifts. The maxima from all three trajectories are within 0.07 eV of each other, showing that configurations sampled with the QUBEKit and revQUBEKit FFMD have similar energy gaps as the QM/MM AIMD configurations.