Measuring internal electric fields with atomic resolution

This paper describes a scheme for analyzing the effects of external electric field on the excitation energy of a conjugated probe molecule that is faithful to the actual microscopic situation and treats all aspects of the problem consistently. Structure is obtained from a molecular mechanics simulation, internal and local fields are calculated by classical electrostatics, and shifts in excitation energy are calculated by incorporating site energies into a simple π-electron model. An example calculation demonstrates the ability of this procedure to determine microscopic electric fields and molecular charge distributions.