Conserving GW scheme for nonequilibrium quantum transport in molecular contacts

TL;DR

This paper presents a GW-based scheme for nonequilibrium quantum transport in molecular contacts, demonstrating improved accuracy in describing correlation effects, Kondo resonance, and molecule-lead interactions compared to traditional methods.

Contribution

The authors develop a conserving, self-consistent GW scheme within the non-equilibrium formalism, incorporating an effective spin-dependent interaction to reduce self-interaction errors.

Findings

GW describes the Kondo resonance well at equilibrium for intermediate interactions.

One-shot G0W0 can produce significant errors at high bias out of equilibrium.

GW predicts a reduced HOMO-LUMO gap with increased molecule-lead coupling.

Abstract

We give a detailed presentation of our recent scheme to include correlation effects in molecular transport calculations using the GW approximation within the non-equilibrium Keldysh formalism. We restrict the GW self-energy to the central region, and describe the leads by density functional theory (DFT). A minimal basis of maximally localized Wannier functions is applied both in the central GW region and the leads. The importance of using a conserving, i.e. fully self-consistent, GW self-energy is demonstrated both analytically and by numerical examples. We introduce an effective spin-dependent interaction which automatically reduces self-interaction errors to all orders in the interaction. The scheme is applied to the Anderson model in- and out of equilibrium. In equilibrium at zero temperature we find that GW describes the Kondo resonance fairly well for intermediate interaction strengths. Out of equilibrium we demonstrate that the one-shot G0W0 approximation can produce severe errors, in particular at high bias. Finally, we consider a benzene molecule between featureless leads. It is found that the molecule's HOMO-LUMO gap as calculated in GW is significantly reduced as the coupling to the leads is increased, reflecting the more efficient screening in the strongly coupled junction. For the IV characteristics of the junction we find that HF and G0W0[G_HF] yield results closer to GW than does DFT and G0W0[G_DFT]. This is explained in terms of self-interaction effects and life-time reduction due to electron-electron interactions.