The non-linear response of molecular junctions: the polaron model revisited.

A polaron model proposed as a possible mechanism for non-linear conductance (Galperin et al 2005 Nano Lett. 5 125-30) is revisited with the focus on the differences between the weak and strong molecule-lead coupling cases. Within the one-molecule-level model we present an approximate expression for the electronic Green function corresponding to the inelastic transport case, which in the appropriate limits reduces to expressions presented previously for the isolated molecule and for a molecular junction coupled to a slow vibration (static limit). The relevance of considerations based on the isolated molecule limit to understanding properties of molecular junctions is discussed.