Quantitative determination of the total local polarity (charge separation) in molecules

We introduce a polarity index Π that is proposed as a measure of the charge separation in a molecule. Π can be viewed as the average deviation of the electrostatic potential on the surface of the molecule. It permits a quantitative assessment of total local polarity, even in a molecule that has zero dipole moment. In support of our formulation of Π, we show that it is related to an empirical polarity-polarizability parameter and also to the dielectric constant.