Unavoidable failure of point charge descriptions of electronic density changes for out-of-plane distortions

[Display omitted] •Point charges fail to reproduce IR intensities for oop bendings in planar systems.•Point charge models lack an additional degree of freedom due to a CT = 0 constraint.•Atomic dipoles provide the required degree of freedom necessary for the calculation.•This is a proof-of-concept; will hold regardless of the population analyses chosen. Population analyses based on point charge approximations accurately estimating the equilibrium dipole moment will systematically fail when predicting infrared intensities of out-of-plane vibrations of planar molecules, whereas models based on both charges and dipoles will always succeed. It is not a matter of how the model is devised but rather how many degrees of freedom are available for the calculation. Population analyses based on point charges are very limited in terms of the amount of meaningful chemical information they provide, whereas models employing both atomic charges and atomic dipoles should be preferred for molecular distortions. A good model should be able to correctly describe not only static, equilibrium structures but also distorted geometries in order to correctly assess information from vibrating molecules. The limitations of point charge models also hold for distortions much larger than those encountered vibrationally.