First-principles calculation of the thermoelectric figure of merit for [2,2]paracyclophane-based single-molecule junctions

Marius Bürkle, Thomas J. Hellmuth, Fabian Pauly, and Yoshihiro Asai
Phys. Rev. B 91, 165419 – Published 20 April 2015

Abstract

Here we present a theoretical study of the thermoelectric transport through [2,2]paracyclophane-based single-molecule junctions. Combining electronic and vibrational structures, obtained from density functional theory (DFT), with nonequilibrium Green's function techniques allows us to treat both electronic and phononic transport properties at a first-principles level. For the electronic part, we include an approximate self-energy correction, based on the DFT+Σ approach. This enables us to make a reliable prediction of all linear response transport coefficients entering the thermoelectric figure of merit ZT. Paracyclophane derivatives offer a great flexibility in tuning their chemical properties by attaching different functional groups. We show that, for the specific molecule, the functional groups mainly influence the thermopower, allowing us to tune its sign and absolute value. We predict that the functionalization of the bare paracyclophane leads to a largely enhanced electronic contribution ZelT to the figure of merit. Nevertheless, the high phononic contribution to the thermal conductance strongly suppresses ZT. Our work demonstrates the importance to include the phonon thermal conductance for any realistic estimate of the ZT for off-resonant molecular transport junctions. In addition, it shows the possibility of a chemical tuning of the thermoelectric properties for a series of available molecules, leading to equally performing hole- and electron-conducting junctions based on the same molecular framework.

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  • Received 30 December 2014
  • Revised 27 March 2015

DOI:https://doi.org/10.1103/PhysRevB.91.165419

©2015 American Physical Society

Authors & Affiliations

Marius Bürkle1,*, Thomas J. Hellmuth2,3, Fabian Pauly3, and Yoshihiro Asai1

  • 1Nanosystem Research Institute (NRI) ‘RICS’, National Institute of Advanced Industrial Science and Technology (AIST), Umezono 1-1-1, Tsukuba Central 2, Tsukuba, Ibaraki 305-8568, Japan
  • 2Institut für Theoretische Festkörperphysik, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany
  • 3Department of Physics, University of Konstanz, 78457 Konstanz, Germany

  • *marius.buerkle@aist.go.jp

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Issue

Vol. 91, Iss. 16 — 15 April 2015

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