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MCW07 Electronic Level Alignment at Metal-Molecule Contacts with a GW Approach

By Jeffrey B. Neaton

Lawrence Berkeley National Laboratory

Published on

Abstract

Most recent theoretical studies of electron transport in single-molecule junctions rely on a Landauer approach, simplified to treat electron-electron interactions at a mean-field level within density functional theory (DFT). While this framework has proven relatively accurate for certain systems, such as metallic point contacts, the computed conductance often substantially exceeds the measured values for organic molecules. This disagreement has raised questions about the validity of static DFT, inherently a ground state theory, for computing electronic transport properties.

Fundamentally, charge transport through metal-molecule junctions is determined by the electronic coupling of frontier molecular orbitals to extended states in the metal, and their energetic position relative to the Fermi energy. However, frontier molecular levels correspond to electron removal (ionization) and addition (affinity) energies, neither of which can be well described by orbital energies computed with DFT.

Here I will discuss the use of an established, first-principles many-electron self-energy approach, within the GW approximation, to study the impact of correlation on electronic level alignment at physisorbed metal-organic interfaces. I will initially describe results for benzene on graphite, a prototype physisorbed metal-molecule contact for which surface polarization effects are found to drastically modify frontier orbital energies [1]. From these results, a model correlation correction to static DFT resonance energies is developed for weakly-coupled molecular junctions, and then shown to reconcile the conductance of benzenediamine-Au junctions, where the average computed value [2] was found to be about seven times larger than experiment [3].

Bio

Jeffrey B. Neaton leads the Theory group at the Molecular Foundry in LBNL. Jeff received his Ph.D. in Physics from Cornell University in 2000, under the guidance of Neil W. Ashcroft. After a departmental postdoc in the Department of Physics and Astronomy at Rutgers University, he joined the Molecular Foundry at Lawrence Berkeley National Laboratory in 2003. His current research interests center on computational nanoscience, in particular the development and application of methods for calculating the structural, spectroscopic, and transport properties of inorganic and molecular nanostructures, particularly at interfaces and contacts. Present areas of interest include the electronic properties of the metal-organic interface, hybrid silicon-organic interfaces, and single-molecule junctions; self-assembly; nanoparticle assemblies; photovoltaics; hydrogen storage; ultrathin epitaxial films of transition metal oxides, such as ferroelectrics and multiferroics; and structural and electronic phases of light elements under pressure.

References

  1. J. B. Neaton, M. S. Hybertsen, and S. G. Louie, Phys. Rev. Lett. 97, 216405 (2006).
  2. S. Y. Quek, L. Venkataraman, H. J. Choi, S. G. Louie, M. S. Hybertsen, and J. B. Neaton, submitted (2007).
  3. L. Venkataraman, J. E. Klare, C. Nuckolls, M. S. Hybertsen, and M. L. Steigerwald, Nature 442, 904 (2006).

Cite this work

Researchers should cite this work as follows:

  • Jeffrey B. Neaton (2007), "MCW07 Electronic Level Alignment at Metal-Molecule Contacts with a GW Approach," http://nanohub.org/resources/3094.

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Burton Morgan Building, Purdue University, West Lafayette, IN

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