  We present a consistent theory of energy balance and conversion in a
single-molecule junction with strong interactions between electrons on the
molecular linker (dot) and phonons in the nuclear environment where the
Marcus-type electron hopping processes predominate in the electron transport.
It is shown that the environmental reorganization and relaxation that accompany
electron hopping energy exchange between the electrodes and the nuclear
(molecular and solvent) environment may bring a moderate local cooling of the
latter in biased systems. The effect of a periodically driven dot level on the
heat transport and power generated in the system is analyzed and energy
conservation is demonstrated both within and beyond the quasistatic regime.
Finally, a simple model of atomic scale engine based on a Marcus
single-molecule junction with a driven electron level is suggested and
discussed.
