Local ionization energy and local polarizability

We investigate relationships between molecular polarizability α, volume V, ionization energy I, and average local ionization energy I( ). The last of these is a measure of the energy required to remove an electron from any point in the space of an atom or molecule. Molecular polarizability shows a good direct correlation with volume, which can be improved to a minor extent by including an inverse dependence on I and more so by using I( ) averaged over the surface of the molecule, IS,ave. The pattern of I( ) on a molecular surface, IS( ), exhibits significant variability, and it is shown through a series of examples that this can be related to the electronic structure of the molecule and to local polarizability. Thus, IS( ) will provide a means of assessing the transferability of regional (e.g., group/bond) polarizabilities from one molecule to another.