Ab initio analysis of electron-phonon coupling in molecular devices

TL;DR

This paper presents a first-principles computational approach to analyze how electron-phonon interactions influence charge transport in molecular devices under bias, revealing key vibrational modes and their coupling variations.

Contribution

It introduces a novel ab initio framework combining density functional theory and nonequilibrium Green's functions to study electron-phonon coupling in molecular electronics.

Findings

Low-lying vibrational modes dominate charge transport.

Electron-phonon coupling strength varies significantly with bias voltage.

Vibrational spectrum changes are minimal under bias.

Abstract

We report first principles analysis of electron-phonon coupling in molecular devices under external bias voltage and during current flow. Our theory and computational framework are based carrying out density functional theory within the Keldysh nonequilibrium Green's function formalism. We analyze which molecular vibrational modes are most relevant to charge transport under nonequilibrium conditions. For a molecular tunnel junction of a 1,4-benzenedithiolate molecule contacted by two leads, the low-lying modes of the vibration are found to be most important. As a function of bias voltage, the electron-phonon coupling strength can change drastically while the vibrational spectrum changes at a few percent level.