Green’s function methods for single molecule junctions

Cohen, Guy; Galperin, Michael

doi:10.1063/1.5145210

Cited by 62 publications

(51 citation statements)

References 581 publications

(589 reference statements)

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“…Moreover, the understanding of electronic transport at the molecular level is very challenging from experimental point of view. 4 For this reason various computational modeling techniques such as density functional theory (DFT) 5 are an efficient way to probe molecular electronic systems and gain a more fundamental understanding of electron transport and charge distribution.…”

Section: Introductionmentioning

confidence: 99%

Influence of the Contact Geometry and Counterions on the Current Flow and Charge Transfer in Polyoxometalate Molecular Junctions: A Density Functional Theory Study

et al. 2021

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Polyoxometalates (POMs) are promising candidates for molecular electronic applications because (1) they are inorganic molecules, which have better CMOS compatibility compared to organic molecules; (2) they are easily synthesized in a one-pot reaction from metal oxides (MO x ) (where the metal M can be, e.g., W, V, or Mo, and x is an integer between 4 and 7); (3) POMs can self-assemble to form various shapes and configurations, and thus the chemical synthesis can be tailored for specific device performance; and (4) they are redox-active with multiple states that have a very low voltage switching between polarized states. However, a deep understanding is required if we are to make commercial molecular devices a reality. Simulation and modeling are the most time efficient and cost-effective methods to evaluate a potential device performance. Here, we use density functional theory in combination with nonequilibrium Green’s function to study the transport properties of [W 18 O 54 (SO 3 ) 2 ] 4– , a POM cluster, in a variety of molecular junction configurations. Our calculations reveal that the transport profile not only is linked to the electronic structure of the molecule but also is influenced by contact geometry and presence of ions. More specifically, the contact geometry and the number of bonds between the POM and the electrodes determine the current flow. Hence, strong and reproducible contact between the leads and the molecule is mandatory to establish a reliable fabrication process. Moreover, although often ignored, our simulations show that the charge balancing counterions activate the conductance channels intrinsic to the molecule, leading to a dramatic increase in the computed current at low bias. Therefore, the role of these counterions cannot be ignored when molecular based devices are fabricated. In summary, this work shows that the current transport in POM junctions is determined by not only the contact geometry between the molecule and the electrode but also the presence of ions around the molecule. This significantly impacts the transport properties in such nanoscale molecular electronic devices.

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Section: Introductionmentioning

confidence: 99%

Influence of the Contact Geometry and Counterions on the Current Flow and Charge Transfer in Polyoxometalate Molecular Junctions: A Density Functional Theory Study

et al. 2021

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“…This can have severe effects on (and provide opportunities for control of) electronic properties of molecule‐metal interfaces in solid‐state systems where functionality depends on such symmetries, such as dipole matrix elements in optoelectronics or non‐equilibrium Green's functions in molecular electronics. [ 56 ]…”

Section: Discussionmentioning

confidence: 99%

Long‐Range Surface‐Assisted Molecule‐Molecule Hybridization

Castelli

Hellerstedt

Krull

et al. 2021

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Metalated phthalocyanines (Pc's) are robust and versatile molecular complexes, whose properties can be tuned by changing their functional groups and central metal atom. The electronic structure of magnesium Pc (MgPc)—structurally and electronically similar to chlorophyll—adsorbed on the Ag(100) surface is investigated by low‐temperature scanning tunneling microscopy and spectroscopy, non‐contact atomic force microscopy, and density functional theory. Single, isolated MgPc's exhibit a flat, fourfold rotationally symmetric morphology, with doubly degenerate, partially populated (due to surface‐to‐molecule electron transfer) lowest unoccupied molecular orbitals (LUMOs). In contrast, MgPc's with neighbouring molecules in proximity undergo a lift of LUMOs degeneracy, with a near‐Fermi local density of states with reduced twofold rotational symmetry, indicative of a long‐range attractive intermolecular interaction. The latter is assigned to a surface‐mediated two‐step electronic hybridization process. First, LUMOs interact with Ag(100) conduction electrons, forming hybrid molecule‐surface orbitals with enhanced spatial extension. Then, these delocalized molecule‐surface states further hybridize with those of neighbouring molecules. This work highlights how the electronic structure of molecular adsorbates—including orbital degeneracies and symmetries—can be significantly altered via surface‐mediated intermolecular hybridization, over extended distances (beyond 3 nm), having important implications for prospects of molecule‐based solid‐state technologies.

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“…However, it has enabled us to recognise that conduction in a specific device can be understood in terms of internal molecular channels associated with the molecular orbitals, that these channels produce the peaks in the transmission spectrum, and can be classified according to a small set of conduction cases 76 depending upon the multiplicities of the roots of the structural polynomials (SPs) defined in Eq. (8). Furthermore, internal channels can be classified as inert or active.…”

Section: Ssp Transmissionmentioning

confidence: 99%

A Correlated Source-Sink-Potential Model Consistent with the Meir–Wingreen Formula

Pickup

Fowler

2020

J. Phys. Chem. A

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We model a molecular device as a molecule attached to a set of leads treated at the tightbinding level, with the central molecule described to any desired level of electronic structure theory. Within this model, in the absence of electron-phonon interactions, the Landauer-Büttiker part of the Meir-Wingreen formula is shown to be sufficient to describe the transmission factor of the correlated device. The key to this demonstration is to ensure that the correlation selfenergy has the same functional form as the exact correlation self-energy. This form implies that non-symmetric contributions to the Meir-Wingreen formula vanish, and hence conservation of current is achieved without the need for Green's Function self-consistency. An extension of the Source-Sink-Potential (SSP) approach gives a computational route to the calculation and interpretation of electron transmission in correlated systems. In this picture, current passes through internal molecular channels via resonance states with complex-valued energies. Each resonant state arises from one of the states in the Lehmann expansion of the one-electron Green's Function, hole conduction deriving from ionised states, and particle conduction from attached states. In the correlated device, the dependence of transmission on electron energy is determined by four structural polynomials, as it was in the tight-binding (Hückel) version of the SSP method. Hence, there are active and inert conduction channels (in the correlated case, linked to Dyson orbitals) governed by a set of selection rules that map smoothly onto the simpler picture.

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Green’s function methods for single molecule junctions

Cited by 62 publications

References 581 publications

Influence of the Contact Geometry and Counterions on the Current Flow and Charge Transfer in Polyoxometalate Molecular Junctions: A Density Functional Theory Study

Influence of the Contact Geometry and Counterions on the Current Flow and Charge Transfer in Polyoxometalate Molecular Junctions: A Density Functional Theory Study

Long‐Range Surface‐Assisted Molecule‐Molecule Hybridization

A Correlated Source-Sink-Potential Model Consistent with the Meir–Wingreen Formula

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