Conserving GW scheme for nonequilibrium quantum transport in molecular contacts

By Kristian Sommer Thygesen, Á. Rubio. 2007

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quasiparticle self-energy, but for practical reasons, we mainly specialize to the so-called GW self-energy, widely used to describe the quasiparticle band structures and spectroscopic properties of extended and lowdimensional systems. We restrict the GW self-energy to a finite, central region containing the molecule, and we 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 numerically. 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 highest occupied molecular orbital‐lowest unoccupied molecular orbital 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 I-V characteristics of the junction, we find that Hartree‐Fock HF and G0W0GHF yield results closer to GW than does DFT and G0W0GDFT. This is explained in terms of selfinteraction effects and lifetime reduction due to electron-electron interactions.

Subfields: Atomic and Molecular Physics, and Optics, Electrical and Electronic Engineering

View Paper: https://www.semanticscholar.org/paper/5839056381c0fb46b69a2a29c03d16133ed760f2