Spectroscopy of transmission resonances through a C₆₀ junction

Role of the Binding Motifs in the Energy Level Alignment and Conductance of Amine-Gold Linked Molecular Junctions within DFT and DFT + Σ

We investigate, using density functional theory (DFT), the electronic and conducting properties of benzenediamine connected to gold electrodes via different tip structures. We examine a series of binding motifs to the electrodes and calculate the junction spectral properties. We consider corrections to the position of molecular resonances at the junction and discuss different approaches to the calculation of these shifts. We relate the magnitude of these corrections to resonance energies to the atomistic structure of the tip. Benzenediamine DFT-based transmission spectra can be well approximated by a Lorentzian model involving only the highest occupied molecular orbital (HOMO). We show how benzenediamine calculated conductance values in quantitative agreement with previous experiments can be achieved from the combination of DFT-based spectra and corrections to the DFT-based HOMO energy and an accessible Lorentzian model.

Charge transport pathways in metal porphyrin as interplay between long and short range scattering processes

We have investigated the ballistic transport for Mn, Fe-porphyrin molecules in contact with Au(111) electrodes by using density functional theory. We show that the information resulted from the projected density of electronic states does not provide a complete picture of the transport mechanism. Instead, we propose a methodology based on the concept of the orbital projected transmissions for selected groups of atoms. We have found that the transmission channels for occupied states can be assigned to short range scattering processes at gold-molecule interface, while for the states above Fermi level the transmission takes place via long range scattering processes. The interplay between these two conduction mechanisms is responsible for the transport path in metal-porphyrin; our model is in qualitative agreement with the existing experimental data on transport pathway on single porphyrin molecules.

Unconventional Current Scaling and Edge Effects for Charge Transport through Molecular Clusters

Metal-molecule-metal junctions are the key components of molecular electronics circuits. Gaining a microscopic understanding of their conducting properties is central to advancing the field. In the present contribution, we highlight the fundamental differences between single-molecule and ensemble junctions focusing on the fundamentals of transport through molecular clusters. In this way, we elucidate the collective behavior of parallel molecular wires, bridging the gap between single molecule and large-area monolayer electronics, where even in the latter case transport is usually dominated by finite-size islands. On the basis of first-principles charge-transport simulations, we explain why the scaling of the conductivity of a junction has to be distinctly nonlinear in the number of molecules it contains. Moreover, transport through molecular clusters is found to be highly inhomogeneous with pronounced edge effects determined by molecules in locally different electrostatic environments. These effects are most pronounced for comparably small clusters, but electrostatic considerations show that they prevail also for more extended systems.