Quantum conductance of 4,4-bipyridine molecular junctions: Role of electrode work function and local d band

J.M.C. Rauba, Mikkel Strange, Kristian Sommer Thygesen

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Abstract

We present density-functional theory calculations for the geometry and conductance of 4,4-bipyridine (BPD) nanojunctions with Au and Pt electrodes. The fact that transport takes place via bipyridine's lowest unoccupied molecular orbital (LUMO) suggests that the Au-BPD junction should have larger conductance than the Pt-BPD junction due to the smaller work function of Au as compared to Pt. On the other hand, coupling to the local d band is stronger in the case of Pt and this broadens the LUMO resonance. We find that these effects largely outbalance each other leading to conductances of 0.01G(0) and 0.02G(0) for the Au and Pt contacts, respectively (G(0)=2e(2)/h is the conductance quantum). The effect of coupling to the electrodes is investigated by means of the group orbital which makes precise the concept of the local band. The construction allows us to explain and rationalize the first-principles results within a simple single-level model.
Original languageEnglish
JournalPhysical Review B Condensed Matter
Volume78
Issue number16
Pages (from-to)165116
ISSN0163-1829
DOIs
Publication statusPublished - 2008

Bibliographical note

Copyright 2008 American Physical Society

Keywords

  • TRANSPORT
  • DEVICES
  • FORMALISM

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