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.
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.
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.
The DACAPO pseudopotential plane-wave code, SIESTA local orbital basis code, GPAW real-space PAW code, the Python Atomic Simulation Environment (ASE)
DFT, Non-equilibrium Green’s functions (Keldysh), Landauer-Büttiker, MD simulations (Langevin), Wannier function analysis, …
Available research projects:
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)
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)