  We study charge and energy transfer in two-site molecular electronic
junctions in which electron transport is assisted by a vibrational mode. To
understand the role of mode harmonicity/anharmonicity on transport behavior, we
consider two limiting situations: (i) the mode is assumed harmonic, (ii) we
truncate the mode spectrum to include only two vibrational levels, to represent
an anharmonic molecular mode. Based on the models' cumulant generating
functions, we analyze the linear-response and nonlinear performance of these
junctions and demonstrate that while the electrical and thermal conductances
are sensitive to whether the mode is harmonic/anharmonic, the Seebeck
coefficient, the thermoelectric figure-of-merit, and the thermoelectric
efficiency beyond linear response, conceal this information.

Mesoscale and Nanoscale Physics;Statistical Mechanics