where ωi is the vibrational frequency, T is the temperature, and pi(T) is the Bose-Einstein population at T, which is equal to unity at T = 0. Equation ( ) gives us a way to account for zero-point vibrations by looking at only two characteristic geometries modulated from the equilibrium by ±σi(0), as shown by Hele et al. We find that the static binding approximation holds reasonably well across Thiel's set (Figures and): in 18 out of 30 molecules (Figure -o and S1a-d; green background), all normal modes with a notable ΔES1 can be diagnosed from ΔEgap, with most of these points being close to the ΔEgap = ΔES1 diagonal (usually R 2 > 0.8). In six further cases (Figure ), most vibrations with a significant ΔES1 can be easily identified from ΔEgap, but the importance of a single stretching (~1600 cm - 1 ; black arrow in Figure ) vibration is consistently underestimated. Finally, the static binding approximation does not hold (Figure -x and S1e-f; orange background) in very small molecules due to their tightly bound excitons (e.g. ethene or cyclopropane), and it fails in 7H-purin-6-amine (Figure ), where stretching vibrations modulate the exciton binding in a non-trivial way. Our results (Figure ) illustrate that in most small organic molecules only a few (usually <15%) normal modes are strongly coupled to frontier orbitals. ΔEgap can be used to identify the vibration most strongly coupled to frontier orbitals with high confidence (excluding very small systems), and in the majority of cases it correctly identifies vibrations strongly coupled with electronic structure, without resorting to excited-state calculations. Furthermore, as the exciton binding energy decreases with molecular size, we expect the static binding approximation to be even more accurate in molecules larger than those investigated here. Therefore, when a description of molecular properties beyond the geometry is desired, we suggest using ΔEgap to identify normal modes which are likely to affect the electronic structure. A limitation of ΔEgap is that it is harmonic, i.e. it can only determine the size of the orbital coupling, and the calculation of its asymmetry requires excited state calculations.