Electronic structural basis for the atomic partial charges of planar molecular systems derived from out-of-plane...

The method of deriving atomic partial charges from out-of-plane dipole derivatives has gained renewed interest as a useful method for identifying the changes in charge distribution upon molecular motion. To understand the nature of those atomic partial charges and to explore possible wide applicability of this method, the modulations in the electron density induced by out-of-plane atomic displacements are analyzed by calculating two-dimensional electronic polarization derivatives. It is shown that their amplitudes are substantially delocalized to the spatial regions of the adjacent atoms, suggesting the size of the planar region required for applying this method to locally planar systems, such as the peptide group capped by alkyl groups. It is also shown that, in molecular complexes, the amplitudes of electronic polarization derivatives are affected rather strongly by the polarization effect, indicating the way to use this method to estimate the extent of intermolecular charge transfer in hydrogen-bonded systems.