Electronic transportation through asymmetrically substituted oligo(phenylene ethynylene)s: Studied by first principles nonequilibrium Green’s function formalism

Abstract

Theoretical investigations of a series of asymmetrically substituted conducting molecular wires [oligo(phenylene ethynylene)s] have been carried out using density functional theory and nonequilibrium Green's function formalism. To get the molecular rectification, the electron-donating group (-NH2) and the electron-withdrawing group (-NO2) are placed on the different positions of the molecular wire. The dependences of spatial distribution and lowest unoccupied molecular orbital (LUMO) energy level on the applied voltage have been found playing dominating but opposite roles in controlling the rectification behavior. In the tested bias range, since the shift LUMO energy level is more important, the electrons transfer more easily from donor to acceptor through the molecular junction in general.

Length‐Dependent Conductance of Molecular Wires and Contact Resistance in Metal–Molecule–Metal Junctions

“…[54] Each molecular model was then sandwiched between two equilateral triangles of Au atoms, with an Au-Au bond length of 2.88 . [55,56] The thiol group loses a hydrogen atom when attached to the metal surface, thus forming a strong covalent bond that provides a good electrical contact between the molecule and the electrodes. Each sulfur atom was chemisorbed in the local energy minimum, that is, the hollow site on the Au clusters.…”

“…Each sulfur atom was chemisorbed in the local energy minimum, that is, the hollow site on the Au clusters. [55][56][57][58][59][60][61] In this configuration, the small Au clusters were used to simulate the attachment to the AuA C H T U N G T R E N N U N G (111) surfaces. The relative positions of the Au atoms were frozen in each triangle, but the distances between the two clusters were relaxed during geometric optimization.…”

The Diversity of Electron‐Transport Behaviors of Molecular Junctions: Correlation with the Electron‐Transport Pathway

“…[32] Each extended model consisted of an organic molecule sandwiched between two Au clusters (see the Supporting Information), with an AuÀAu bond length of 2.88 . [26,31,[33][34][35] The conjugated molecule was chemisorbed in the local energy minimum: the hollow site on the Au clusters with an AuÀS bond. [36,37] In this configuration, the small Au clusters were used for simulating the attachment to the Au(111) surfaces.…”

Nonequilibrium Green’s function study on the electronic structure and transportation behavior of the conjugated molecular junction: Terminal connections and intramolecular connections

“…In each model, the molecule was sandwiched between two equilateral triangles of Au atoms, with an Au-Au bond length of 2.88 Å. 10,31,32 The thiol lost a hydrogen atom when it attached to the gold triangle, making a strong covalent bond with Au atoms, providing the good electrical contact between the organic molecule and the metal electrode. In our calculation, we considered sulfur atom chemisorbed at the hollow site of the Au cluster, which is energetically favorable.…”

“…After positioning the molecule perpendicularly to the Au surface, the favorable moleculeelectrode contact distance was fixed at 2.0 Å within the computational accuracy used by most researchers. 10,31,32,35 For DFT electronic structure calculation, we used the TroullierMartins nonlocal pseudopotentials for core electrons, 36 double-plus polarization basis set for the organic molecules, and single-plus polarization basis set for the Au electrodes. The local density approximation was used for the electron exchange and correlation.…”