Thermoelectricity in molecular junctions with harmonic and anharmonic modes

TL;DR

This study investigates how harmonic and anharmonic vibrational modes affect charge and energy transfer in molecular junctions, revealing that certain thermoelectric properties are insensitive to mode anharmonicity.

Contribution

It introduces models comparing harmonic and anharmonic vibrational modes in molecular junctions and analyzes their impact on thermoelectric performance.

Findings

Electrical and thermal conductances depend on mode harmonicity.

Seebeck coefficient and thermoelectric efficiency are insensitive to mode anharmonicity.

Mode harmonicity influences linear and nonlinear transport behaviors.

Abstract

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.