Kurt Stokbro

Density-functional method for nonequilibrium electron transport

We describe an ab initio method for calculating the electronic structure, electronic transport, and forces acting on the atoms, for atomic scale systems connected to semi-infinite electrodes and with an applied voltage bias. Our method is based on the density-functional theory (DFT) as implemented in the well tested SIESTA approach (which uses nonlocal norm-conserving pseudopotentials to describe the effect of the core electrons, and linear combination of finite-range numerical atomic orbitals to describe the valence states). We fully deal with the atomistic structure of the whole system, treating both the contact and the electrodes on the same footing. The effect of the finite bias (including self-consistency and the solution of the electrostatic problem) is taken into account using nonequilibrium Greens functions. We relate the nonequilibrium Greens function expressions to the more transparent scheme involving the scattering states. As an illustration, the method is applied to three systems where we are able to compare our results to earlier ab initio DFT calculations or experiments, and we point out differences between this method and existing schemes. The systems considered are: (i) single atom carbon wires connected to aluminum electrodes with extended or finite cross section, (ii) single atom gold wires, and finally (iii) large carbon nanotube systems with point defects.

Conductance switching in a molecular device: The role of side groups and intermolecular interactions

We report first-principles studies of electronic transport in monolayers of Tour wires functionalized with different side groups. An analysis of the scattering states and transmission eigenchannels suggests that the functionalization does not strongly affect the resonances responsible for current flow through the monolayer. However, functionalization has a significant effect on the interactions within the monolayer, so that monolayers with NO 2 side groups exhibit local minima associated with twisted conformations of the molecules. We use our results to interpret observations of negative differential resistance and molecular memory in monolayers of NO 2 functionalized molecules in terms of a twisting of the central ring induced by an applied bias potential.

TranSIESTA: A Spice for Molecular Electronics

Abstract: Our recently developed method, TranSIESTA, enables modelling of molecular electronic devices under operation conditions. The method is based on density functional theory, and calculates the self‐consistent electronic structure of a nanostructure coupled to three‐dimensional electrodes with different electrochemical potentials. It uses a full atomistic ab initio description of both the electrodes and the nanoscale device. The calculations reveal information about the scattering states, transmission coefficients, electron current, and non‐equilibrium forces in the systems. In this paper we use the method to investigate the electrical properties of three ring phenyl‐ethynylene oligomers (OPE). We present results for the electrical effect of side groups and molecular conformations of the molecules. The calculations indicate that molecular switching and negative differential conductance (NDC) are related to rotations of the middle phenyl ring.

STM-Induced Hydrogen Desorption via a Hole Resonance

We report STM-induced desorption of H from

First-principles modeling of electron transport

\mathrm{Si}\left(100\right)\ensuremath{-}\mathrm{H}\left(2\ifmmode\times\else\texttimes\fi{}1\right)

Nonlinear conductance in molecular devices : Molecular length dependence

at negative sample bias. The desorption rate exhibits a power-law dependence on current and a maximum desorption rate at

Improved initial guess for minimum energy path calculations

\ensuremath{-}7\mathrm{V}

Origin of current-induced forces in an atomic gold wire: A first-principles study

. The desorption is explained by vibrational heating of H due to inelastic scattering of tunneling holes with the Si-H

First-principles theory of inelastic currents in a scanning tunneling microscope

5\ensuremath{\sigma}

First-Principles Modeling of Molecular Single-Electron Transistors

hole resonance. The dependence of desorption rate on current and bias is analyzed using a novel approach for calculating inelastic scattering, which includes the effect of the electric field between tip and sample. We show that the maximum desorption rate at