In the molecular electronics group of CAMD we focus on the electronic, chemical and mechanical properties of nano-scale devices such as single-molecule junctions, nanowires, and nanotubes. Such systems are technologically important due to their potential application as nano-scale chemical sensors and molecular electronic components such as transistors, memory elements, and rectifiers.

 

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Research

Our research is divided into three main areas:

 

 

 

• First-principles modelling of electron transport in nano-scale contacts:

 

 

Using a combination of non-equilibrium Green’s functions and density functional theory (DFT) we perform first-principles simulations of electron transport in nano-scale devices such as metal point contacts, atomic wires and single-molecule junctions. The electronic structure of the entire system is described at the Kohn-Sham level of DFT, and the Hamiltonian and Green’s functions are evaluated in terms of a basis consisting of maximally localized Wannier functions or numerical atomic orbitals depending on the desired accuracy:speed. Key issues are: the role of the contacts, identification of the transport mechanism, i.e. which orbitals carry the current, correlations between atomic- and electronic structures.

 

 

 

• Mechanical and chemical properties of nano-contacts:

 

 

The mechanical and chemical properties of metal contacts and chains are modelled using molecular dynamics simulations. This is a central theme as molecular junctions are often formed by pulling a metal contact apart.  We use effective medium potentials and ab initio molecular dynamics simulations to address the formation and stability of the contacts, and address their chemical properties using DFT. 

 

 

 

 

 

 

• Transport and many-body perturbation theory:

 

In order to address many-body effects that are not captured by the DFT-transport approach we are combining the Keldysh non-equilibrium Green’s function technique with many-body perturbation theory. Applications of this approach are inclusion of electron-electron correlations at the level of the GW approximation as well as inelastic scattering of electrons on local vibrations.

 

 

 

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Computer codes:

The DACAPO pseudopotential plane-wave code, SIESTA local orbital basis code, GPAW real-space PAW code, the Python Atomic Simulation Environment (ASE)

 

Methodology:

DFT, Non-equilibrium Green’s functions (Keldysh), Landauer-Büttiker, MD simulations (Langevin), Wannier function analysis, …

 

       

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Available research projects:

 

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Recent Publications 

M. Strange, K. S. Thygesen, J. P. Sethna, and K. W. Jacobsen: Anomalous conductance oscillations and half-metallicity of atomic Ag-O chains  Phys. Rev. Lett. 101, 096804 (2008)

 

J. M. Garcia-Lastra, K. S. Thygesen, M. Strange, and A. Rubio: Conductance of Sidewall-Functionalized Carbon Nanotubes: Universal Dependence on Adsorption Sites, Phys. Rev. Lett. 101, 236806 (2008)

 

I. S. Kristensen, D. J. Mowbray, K. S. Thygesen, and K. W. Jacobsen: Comparative study of anchoring groups for molecular electronics: Structure and conductance of Au-S-Au and Au-NH2-Au junctions,  J. Phys.: Condens. Matter 20, 374101 (2008)

 

K. S. Thygesen: Impact of exchange-correlation effects on the IV characteristsics of a molecular junction, Phys. Rev. Lett. 100, 166804 (2008) 

 

D. J. Mowbray, G. Jones, and K. S. Thygesen: Influence of functional groups on charge transport in molecular junctions. J. Chem. Phys, 128, 111103 (2008)

 

M. Strange, I. S. Kristensen, K. S. Thygesen, and K. W. Jacobsen: Benchmark density functional theory calculations for nanoscale conductance. J. Chem. Phys, 128, 114714 (2008)

 

K. S. Thygesen and A. Rubio: Conserving GW scheme for Non-Equilibrium Quantum Transport in Molecular Contacts, Phys. Rev. B 77, 115333 (2008)

 

K. S. Thygesen and A. Rubio: Non-equilibrium GW approach to quatum transport in nano-scale contacts, Journal of Chemical Physics 126, 091101 (2007)

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M. Strange, K. S. Thygesen, and K. W. Jacobsen: Electron transport in a Pt-CO-Pt nanocontact: Density functional theory calculations, Phys. Rev. B 73, 125424 (2006)

 

K. S. Thygesen: Electron transport through an interacting region: The case of a nonorthogonal basis set, Phys. Rev. B 73, 035309 (2006)

 

R. Stadler, K. S. Thygesen, and K. W. Jacobsen: Forces and conductances in a single-molecule bipyridine junction, Phys. Rev. B 72, 241401(R) (2005)

 

K. S. Thygesen, L. B. Hansen, and K. W. Jacobsen: Partly occupied Wannier functions: Construction and applications, Phys. Rev. B 72, 125119 (2005)

 

K. S. Thygesen and K. W. Jacobsen: Molecular transport calculations with Wannier functions, Chemical Physics 319, 111-125 (2005)

 

K. S. Thygesen and K. W. Jacobsen: Interference and k-point sampling in the supercell approach to phase-coherent transport, Phys. Rev. B 72, 033401 (2005)

 

R. Stadler, K. S. Thygesen, and K. W. Jacobsen: An ab initio study of electron transport through nitrobenzene: the influence of leads and contacts, Nanotechnology 16, S155 (2005)

 

D. Djukic, K. S. Thygesen, C. Untiedt, R. H. M. Smit, K. W. Jacobsen, and J. M. van Ruitenbeek: Stretching dependence of the vibration modes of a single-molecule Pt-H2–Pt bridge, Phys. Rev. B 71, 161402(R) (2005)

 

K. S. Thygesen and K. W. Jacobsen: Conductance Mechanism in a Molecular Hydrogen Contact, Phys. Rev. Lett. 94, 036807 (2005)

 

K. S. Thygesen, L. B. Hansen, and K. W. Jacobsen: Partly Occupied Wannier Functions, Phys. Rev. Lett. 94, 026405 (2005)