Vibrational Excitations in Weakly Coupled Single-Molecule Junctions: A Computational Analysis

Abstract

In bulk systems, molecules are routinely identified by their vibrational spectrum using Raman or infrared spectroscopy. In recent years, vibrational excitation lines have been observed in low-temperature conductance measurements on single-molecule junctions, and they can provide a similar means of identification. We present a method to efficiently calculate these excitation lines in weakly coupled, gateable single-molecule junctions, using a combination of ab initio density functional theory and rate equations. Our method takes transitions from excited to excited vibrational state into account by evaluating the Franck-Condon factors for an arbitrary number of vibrational quanta and is therefore able to predict qualitatively different behavior from calculations limited to transitions from ground state to excited vibrational state. We find that the vibrational spectrum is sensitive to the molecular contact geometry and the charge state, and that it is generally necessary to take more than one vibrational quantum into account. Quantitative comparison to previously reported measurements on pi-conjugated molecules reveals that our method is able to characterize the vibrational excitations and can be used to identify single molecules in a junction. The method is computationally feasible on commodity hardware.

Charge transport through single molecules, quantum dots and quantum wires

“…Also, the approach outlined here can be extended to other transport quantities, such as spin and heat [74]. The molecule and junction models used here can be parametrized based on atomistic electronic structure calculations, as for instance, in [17,75,76]. Pursuing this further is another important step in understanding molecular quantum dots.…”

Sub-Ohmic to super-Ohmic crossover behavior in nonequilibrium quantum systems with electron-phonon interactions

“…The latter are held at a different chemical potentials and thus provide the source to drive the system away from equilibrium. Most studies focused on steady-state properties utilizing a variety of techniques to describe, e.g., Franck-Condon blockade, [39][40][41][42][43] negative differential resistance, [44][45][46][47][48] or the existence of multiple long-lived solutions, i.e. bistability.…”

Performance analysis of impurity added benzene based single-electron transistor

“…The ultra small size of SET will allow the designers to integrate more number of transistors on a chip. In recent years, researchers have started focusing on the use of the organic molecules as island in the single-electron transistor (Stokbro 2010;Brandbyge et al 2002;Neaton et al 2006;Seldenthuis et al 2010;Parashar et al 2012). …”