  Experimental studies on single-molecule junctions are typically in need of a
simple theoretical approach that can reproduce or be fitted to experimentally
measured transport data. In this context, the single-level variant of the
Landauer approach is most commonly used but methods based on Marcus theory are
also gaining in popularity. Recently, a generalized theory unifying these two
approaches has also been developed. In the present work, we extend this theory
so that it includes entropic effects (which can be important when polar
solvents are involved, but are likely minor for solid-state systems). We
investigate the temperature-dependence of the electric current and compare it
to the behavior predicted by the Landauer and the conventional Marcus theory.
We argue that this generalized theory provides a simple yet effective framework
for understanding charge transport through molecular junctions. Furthermore, we
explore the role of the entropic effects in different transport regimes and
suggest experimental criteria for detecting them in solvated molecular
junctions. Lastly, in order to account for nuclear tunnelling effects, we also
demonstrate how lifetime broadening can be introduced into the
Marcus-Levich-Dogonadze-Jortner-type description of electron transport.
