Towards quantitative accuracy in first-principles transport calculations: The GW method applied to alkane/gold junctions

TL;DR

This paper applies the GW many-body approximation to first-principles calculations of electronic conductance in gold/alkanediamine junctions, achieving better agreement with experiments by accurately aligning molecular energy levels.

Contribution

It demonstrates the effectiveness of the GW method over standard DFT in predicting transport properties of molecular junctions, highlighting the importance of dynamical screening effects.

Findings

GW reduces contact conductance G_c compared to DFT.

Better alignment of molecular energy levels with Fermi energy.

Dynamical screening affects delocalized and localized states differently.

Abstract

The calculation of electronic conductance of nano-scale junctions from first principles is a long standing problem in molecular electronics. Here we demonstrate excellent agreement with experiments for the transport properties of the gold/alkanediamine benchmark system when electron-electron interactions are described using the many-body GW approximation. The main difference from standard density functional theory (DFT) calculations is a significant reduction of the contact conductance, G_c, due an improved alignment of the molecular energy levels with the metal Fermi energy. The molecular orbitals involved in the tunneling process comprise states delocalized over the carbon backbone and states localized on the amine end groups. We find that dynamical screening effects renormalize the two types of states in qualitatively different ways when the molecule is inserted in the junction. Consequently, the GW transport results cannot be mimicked by DFT calculations employing a simple scissors operator.