Effective and non-local polarizability response in molecular assemblies

The general non-local polarizability response in a molecular assembly is separated into molecular and intermolecular contributions which lead to a simple approximate response equation involving quantities averaged over molecular volumes Analysis of a Drude oscillator model shows how short-range interactions modify the free molecular response and produce non-local response. The response of a pair of interacting molecules is derived: the total pair polarizability cannot in general be analysed for information on short-range effects. The response of a molecular crystal is also derived: the unit-cell polarizability becomes non-diagonal and contains non-local contributions from more than one molecule on a given sublattice. Applications of these results are outlined.