Non-adiabatic simulations of current-related structural transformations in metallic nanodevices

One of the less explored aspects of molecular electronics is the effect of current on the mechanical stability of the conducting molecule: charge flow can alter both the geometry and electronic properties of the device, modifying the conductance and giving rise to nonlinear conduction characteristics or conductance switching. We performed a fundamental study on the correlation between the geometry and evolving electronic structure of small Au clusters that were embedded in finite Au wires and subjected to periodic transient currents. Both the current-carrying electronic states and the local electronic structure of the model system were described away from the ground state within a time-dependent Ehrenfest formalism. Non-adiabatic molecular dynamics simulations revealed that clusters undergo structural transformations between several representative geometries that coincide with patterns in cluster charging. The shape changes were enabled by the fluctuations in cluster band filling associated with the current and assisted by current-related forces. Metastable configurations of stable clusters were linked to events of charge trapping on the cluster.