Charge mobility in molecules: Charge fluxes from second derivatives of the molecular dipole

On the basis of the analytical model previously suggested by Dinur, we discuss here a method for the calculation of vibrational charge fluxes in planar molecules, obtained as numerical second derivatives of the molecular dipole moment. This model is consistent with the partitioning of the atomic polar tensors into atomic charge and charge fluxes according to the Equilibrium Charges-Charge Fluxes model and it is directly related to experimentally measurable quantities such as IR intensities. On the basis of density functional theory calculations carried out for several small benchmark molecules, the complete set of charge fluxes is calculated for each molecule and compared with the approximated flux parameters previously derived and reported in the past literature. The degree of localization of charge fluxes is investigated and discussed; in addition, some approximations are analyzed in order to verify the applicability of the method to large and/or non-planar molecules, aimed at obtaining a de- scription of the electron charge mobility in different molecular environments.