Current-induced dissociation in molecular junctions beyond the paradigm of vibrational heating: The role of anti-bonding electronic states

TL;DR

This study investigates how current induces bond rupture in molecular junctions, highlighting the dominant role of anti-bonding electronic states over vibrational heating, thus challenging traditional views in molecular electronics.

Contribution

The paper introduces a numerically exact HQME-based approach to distinguish dissociation mechanisms, emphasizing the importance of anti-bonding states over vibrational heating.

Findings

Anti-bonding electronic states significantly contribute to dissociation.

Vibrational heating plays a negligible role when anti-bonding states are accessible.

Current-induced heating is only relevant in non-resonant regimes.

Abstract

The interaction between electronic and nuclear degrees of freedom in single-molecule junctions is an essential mechanism, which may result in the current-induced rupture of chemical bonds. As such, it is fundamental for the stability of molecular junctions and for the applicability of molecular electronic devices. In this publication, we study current-induced bond rupture in molecular junctions using a numerically exact scheme, which is based on the hierarchical quantum master equation (HQME) method in combination with a discrete variable representation for the nuclear degrees of freedom. Employing generic models for molecular junctions with dissociative nuclear potentials, we identify distinct mechanisms leading to dissociation, namely the electronic population of anti-bonding electronic states and the current-induced heating of vibrational modes. Our results reveal that the latter plays a negligible role whenever the electronic population of anti-bonding states is energetically possible. Consequently, the significance of current-induced heating as a source for dissociation in molecular junctions involving an active anti-bonding state is restricted to the non-resonant transport regime, which reframes the predominant paradigm in the field of molecular electronics.