Effective field theory of interacting π electrons

We develop a π-electron effective field theory (π-EFT) wherein the two-body Hamiltonian for a π-electron system is expressed in terms of three effective parameters: the π-orbital quadrupole moment, the on-site repulsion, and a dielectric constant. As a first application of this π-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 π-EFT to calculate the differential conductance spectrum of the prototypical benzenedithiol-Au single-molecule junction and the π-electron contribution to the van der Waals interaction between benzene and a metallic electrode.