  A polaron model proposed as a possible mechanism for nonlinear conductance
[Galperin M, Ratner M A, and Nitzan A 2005 Nano Lett. 5 125-30] is revisited
with focus on the differences between the weak and strong molecule-lead
coupling cases. Within the one-molecular level model we present an approximate
expression for the electronic Green function corresponding to inelastic
transport case, which in the appropriate limits reduces to expressions
presented previously for the isolated molecule and for 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.
