  Marcus and Landauer-Buttiker approaches to charge transport through molecular
junctions describe two contrasting mechanisms of electronic conduction. In
previous work, we have shown how these charge transport theories can be unified
in the single-level case by incorporating lifetime broadening into the
second-order quantum master equation. Here, we extend our previous treatment by
incorporating lifetime broadening in the spirit of the self-consistent Born
approximation. By comparing both theories to numerically converged
hierarchical-equations-of-motion (HEOM) results, we demonstrate that our novel
self-consistent approach rectifies shortcomings of our earlier framework which
are present especially in the case of relatively strong electron-vibrational
coupling. We also discuss circumstances under which the theory developed here
simplifies to the generalised theory developed in our earlier work. Finally, by
considering the high-temperature limit of our new self-consistent treatment, we
show how lifetime broadening can also be self-consistently incorporated into
Marcus theory. Overall, we demonstrate that the self-consistent approach
constitutes a more accurate description of molecular conduction while retaining
most of the conceptual simplicity of our earlier framework.
