Effective field theory of interacting π electrons

We develop a pi-electron effective field theory (pi-EFT) wherein the two-body Hamiltonian for a pi-electron system is expressed in terms of three effective parameters: the pi-orbital quadrupole moment, the on-site repulsion, and a dielectric constant. As a first application of this pi-EFT, we develop a model of screening in molecular junctions based on image multipole moments, and use this to investigate the reduction of the HOMO-LUMO gap of benzene. Beyond this, we also use pi-EFT to calculate the differential conductance spectrum of the prototypical benzenedithiol-Au single-molecule junction and the pi-electron contribution to the van der Waals interaction between benzene and a metallic electrode.