On Conductance and Interface Effects in Molecular Devices

On Conductance and Interface Effects in Molecular Devices

Verzijl, C.J.O.

van der Zant, H.S.J. (promotor)
Thijssen, J.M. (promotor)

Applied Sciences

Quantum Nanoscience

2012-11-27

In this dissertation we discuss ab initio studies of quantum transport through single-molecule devices, using a combination of techniques from quantum chemistry and many-body physics. The molecular transport calculations discussed here are based on the "DFT+NEGF" approach to molecular transport. We first outline the density functional theory (DFT) and non-equilibrium Green's functions (NEGF) formalisms. We discuss the assumptions behind their combined use, as well as consequent limitations to the computational results we have obtained. This has been implemented as a custom, scalable extension of the ADF/BAND quantum chemistry package originally developed in the theoretical chemistry group at the VU University Amsterdam, and currently developed and commercialized by Scientific Computing and Modelling N.V. Using this code, we study chains and more complex chemical systems such as multi-ring phenyl junctions and a class of porphyrin-derivative devices recently studied experimentally. To address the polarization effects suspected to be behind the mechanical gating effects observed in the experiments, we extend our transport method with a complementary approach which accounts for image-charge effects at a metal-molecule interface. We close with a further study of the performance of our main method in relation to approximate transport methods based on simplified treatments of the leads in molecular devices.

single-molecule devices
DFT
NEGF
image charges
interface effects
level alignment

https://doi.org/10.4233/uuid:5a6b8240-1033-4834-b947-09c54b0f891b

Casimir PhD Series

2012-12-31

9789085931430

Institutional Repository

doctoral thesis

(c) 2012 Verzijl, C.J.O.