Recently, Bai et al. demonstrated that this approximation does not always hold by showing that computed vertical excitation energies usually shift to lower energies when effects of nuclear motion are included. Alvertis and collaborators 11 found that this gap renormalization is present even at zero Kelvin (zero-point renormalization, or ZPR), and estimated its mean value to -0.35 eV for Thiel's set 4 of small organic molecules, with extreme cases reaching -1.36 eV. They also noted that ZPR can often be reduced to the effect of only several vibrations. A similar conclusion was reached by Lambropoulos et al., who found that ZPR in cyclo [18]carbon can be reduced to the effect of a few bond-stretching vibrational modes. In organic molecular wires, bond stretching and backbone torsion play a large role, as the charge-carrier mobilities are highly dependent on the extent of conjugation modulated by these vibrations. In more general cases, it can be challenging to understand which vibrations are important and which can be neglected.