Image-charge induced localization of molecular orbitals at metal-molecule interfaces: Self-consistent GW calculations

TL;DR

This paper uses self-consistent GW calculations to study how image charge effects influence the localization and energy shifts of molecular orbitals at metal-molecule interfaces, revealing effects not captured by standard methods.

Contribution

It demonstrates the importance of self-consistent GW calculations in accurately modeling image charge effects on molecular orbitals at interfaces.

Findings

Frontier orbitals are pulled toward the metal surface due to image charge effects.

Higher and lower energy orbitals are pushed away from the surface.

Self-consistency in GW is crucial for accurate description of these effects.

Abstract

Quasiparticle (QP) wave functions, also known as Dyson orbitals, extend the concept of single-particle states to interacting electron systems. Here we employ many-body perturbation theory in the GW approximation to calculate the QP wave functions for a semi-empirical model describing a $\pi$-conjugated molecular wire in contact with a metal surface. We find that image charge effects pull the frontier molecular orbitals toward the metal surface while orbitals with higher or lower energy are pushed away. This affects both the size of the energetic image charge shifts and the coupling of the individual orbitals to the metal substrate. Full diagonalization of the QP equation and, to some extent, self-consistency in the GW self-energy, is important to describe the effect which is not captured by standard density functional theory or Hartree-Fock. These results should be important for the understanding and theoretical modeling of electron transport across metal-molecule interfaces.