Effects of vibrational anharmonicity on molecular electronic conduction and thermoelectric efficiency

TL;DR

This paper investigates how vibrational anharmonicity influences electrical and thermoelectric properties in molecular junctions, revealing that conductance is sensitive to anharmonic effects while thermoelectric efficiency remains largely unaffected.

Contribution

It provides a comparative analysis of harmonic and anharmonic vibrational potentials on charge transfer and thermoelectric response in molecular junctions using a quantum master equation approach.

Findings

Electrical and thermal conductances are significantly affected by vibrational anharmonicity.

Seebeck coefficient and thermoelectric efficiency show weak sensitivity to anharmonic effects.

Thermoelectric performance is largely insensitive to vibrational anharmonicity.

Abstract

We study inelastic vibration-assisted charge transfer effects in two-site molecular junctions, focusing on signatures of vibrational anharmonicity on the electrical characteristics and the thermoelectric response of the junction. We consider three types of oscillators: harmonic, anharmonic-Morse allowing bond dissociation, and harmonic-quartic, mimicking a confinement potential. Using a quantum master equation method which is perturbative in the electron-vibration interaction we find that the (inelastic) electrical and thermal conductances can be largely affected by the nature of the vibrational potential. In contrast, the Seebeck coefficient, the thermoelectric figure-of-merit, and the thermoelectric efficiency beyond linear response, conceal this information, showing a rather weak sensitivity to vibrational anharmonicity. Our work illustrates that anharmonic (many-body) effects, consequential to the current-voltage characteristics, are of little effect for the thermoelectric performance.