Carbon nanotube, graphene, nanowire, and molecule-based electron and spin transport phenomena using the non-equilibrium Green function method at the level of first principles theory

TL;DR

This paper introduces a DFT-based non-equilibrium Green function approach for modeling electron and spin transport in nanoscale devices, enabling detailed analysis of I-V characteristics in complex systems.

Contribution

It develops a versatile, self-consistent computational scheme for first-principles electron transport calculations applicable to various nanostructures.

Findings

Successfully modeled quantum conductance in carbon nanotubes and graphene nanoribbons.

Analyzed I-V characteristics of molecular devices with gold electrodes.

Extended the method to large, realistic systems with inelastic scattering considerations.

Abstract

Based on density functional theory (DFT), we have developed algorithms and a program code to investigate the electron transport characteristics for a variety of nanometer scaled devices in the presence of an external bias voltage. We employed basis sets comprised of linear combinations of numerical type atomic orbitals and k-point sampling for the realistic modeling of the bulk electrode. The scheme coupled with the matrix version of the non-equilibrium Green function method enables determination of the transmission coefficients at a given energy and voltage in a self-consistent manner, as well as the corresponding current-voltage (I-V) characteristics. This scheme has advantages because it is applicable to large systems, easily transportable to different types of quantum chemistry packages, and extendable to describe time-dependent phenomena or inelastic scatterings. It has been applied to diverse types of practical electronic devices such as carbon nanotubes, graphene nano-ribbons, metallic nanowires, and molecular electronic devices. The quantum conductance phenomena for systems involving quantum point contacts and I-V curves are described for the dithiol-benzene molecule in contact with two Au electrodes using the k-point sampling method.