Externally modulated electron transport through molecules and nanojunctions

The conductance properties of single molecules connected to macroscopic electrodes can be investigated through quantum transport calculations that utilize non-equilibrium Green's functions (NEGF) in combination with density
functional theory (DFT). Advanced computational techniques [1] enable the incorporation of various external stimuli affecting the molecules, such as bias voltages, electric fields, and chemical environments. This talk presents a series of model systems where the transport properties of atomic components are influenced by external modulation. For instance, applying a bias voltage can
induce tautomerization processes within a molecule, leading to significant alterations in its transport characteristics [2]. Additionally, we explore how a
molecule's conductance properties can vary dramatically depending on whether it is in its neutral or oxidized state [3]. Moreover, we investigate electron transport through two-dimensional graphene nanoribbons under high bias voltages and electric fields, focusing on the diffusion of metal adatoms. We analyze how the bias-induced forces acting on these atoms correlate with changes in electron
density distribution, chemical bonding, and the molecular orbital structure [4]. To illustrate this, we present a simplified molecular model of a metal atom on a benzene ring, which provides insights into the forces at play in the extended
system from an inorganic chemistry perspective. Our findings highlight the efficacy of combining DFT-NEGF calculations with experimental techniques such as mechanical break-junctions and scanning probe microscopy, resulting in a close alignment between theoretical predictions and experimental observations of molecular junctions.

[1] N. Papior et al, Improvements on non-equilibrium and transport Green function techniques: The next-generation transiesta, Com. Phys.Com. 212 , 8–24 (2017)
[2] P. A. Sreelakshmi et al, Field-Induced Sequential Prototropic Tautomerism in Enzyme-like Nanopocket Created by Single Molecular Break Junction, J. Am. Chem. Soc., 146, 51, 35242–35251 (2024)
[3] L.K.I. Rieger et al, High Molecular Conductance and Inverted Conductance Decay over 3 nm in Aminium-Terminated Carbon-Bridged Oligophenylene-Vinylene, J.Am. Chem. Soc. 147, 1, 957–964 (2024)
[4] S. Leitherer et al, Electromigration Forces on Atoms on Graphene Nanoribbons: The Role of Adsorbate-Surface Bonding, JACS Au 4 (1), 189–196 (2024)