Atomistic modeling of dynamical quantum transport

TL;DR

This paper introduces a dynamical quantum transport modeling approach using TD-DFTB, demonstrating its effectiveness on a molecular junction and exploring its response to alternating biases with resonant conductance enhancements.

Contribution

The work develops a time-dependent density functional tight-binding method for quantum transport and validates it against static Landauer calculations, including frequency response analysis.

Findings

Steady state current matches Landauer predictions.

Capacitive behavior observed under alternating bias.

Resonant conductance enhancement at optical frequencies.

Abstract

We present dynamical transport calculations based on a tight-binding approximation to adiabatic time-dependent density functional theory (TD-DFTB). The reduced device density matrix is propagated through the Liouville-von Neumann equation. For the model system, 1,4-benzenediol coupled to aluminum leads, we are able to confirm the equality of the steady state current resulting from a time-dependent calculation to a static calculation in the conventional Landauer framework. We also investigate the response of the junction subjected to alternating bias voltages with frequencies up to the optical regime. Here we can clearly identify capacitive behaviour of the molecular device and a significant resonant enhancement of the conductance. The results are interpreted using an analytical single level model comparing the device transmission and admittance. In order to aid future calculations under alternating bias, we shortly review the use of Fourier transform techniques to obtain the full frequency response of the device from a single current trace.