Plane-wave many-body corrections to the conductance in bulk tunnel junctions

TL;DR

This study investigates how advanced many-body and hybrid functional corrections to electronic structure calculations affect the conductance in bulk metal-insulator-metal junctions, showing improved agreement with experimental data especially at larger insulator thicknesses.

Contribution

It demonstrates that beyond-DFT corrections, particularly HSE and COHSEX, significantly reduce conductance predictions, aligning them more closely with experimental results in tunneling regimes.

Findings

Beyond-DFT corrections reduce zero-bias conductance.

HSE and COHSEX improve agreement with experiments.

Wavefunction corrections impact conductance more than energy corrections.

Abstract

The conductance of bulk metal--insulator--metal junctions is evaluated by the Landauer formula using an \textit{ab initio} electronic structure calculated using a plane-waves basis set within density-functional theory (DFT) and beyond, i.e.\ including exact non-local exchange using hybrid functional (HSE) or many-body $G_0W_0$ and COHSEX quasiparticle (QP) schemes. We consider an Ag/MgO/Ag heterostructure model and we focus on the evolution of the zero-bias conductance as a function of the MgO film thickness. Our study shows that the correction of the electronic structure beyond semi-local density functionals goes in the right direction to improve the agreement with experiments, significantly reducing the zero-bias conductance. This effect becomes more evident at larger MgO thickness, that is in increasing tunneling regime. We also observe that the reduction of the conductance seems more related to the correction of wavefunctions rather than energies, and thus not directly related to the correction of the band-gap of bulk MgO. $G_0W_0$ and HSE both provide a correct band-gap in agreement with experiments, but only HSE gives a significant reduction of the conductance. COHSEX, while overestimating the band-gap, gives a reduction of the conductance very close to HSE.