Asymptotic self-consistency in quantum transport calculations

TL;DR

This paper investigates the inaccuracies in quantum transport simulations caused by neglecting the self-consistent response of leads, demonstrating errors in non-equilibrium properties and proposing a correction scheme.

Contribution

It reveals the impact of ignoring self-consistency in lead electrostatics and introduces a method to improve the accuracy of quantum transport calculations.

Findings

Large errors in non-equilibrium properties for small vacuum gaps

Electrostatic potential approximation is incompatible with charge neutrality

Proposed correction scheme reduces errors significantly

Abstract

Ab-initio simulations of quantum transport commonly focus on a central region which is considered to be connected to infinite, periodic leads through which the current flows. The electronic structure of these distant leads is normally obtained from an equilibrium calculation, ignoring the self-consistent response of the leads to the current. We examine the consequences of this, and show that the electrostatic potential is effectively being approximated by the difference between electrochemical potentials and that this approximation is incompatible with asymptotic charge neutrality. In a test calculation for a simple metal-vacuum-metal junction, we find large errors in the non-equilibrium properties calculated with this approximation, in the limit of small vacuum gaps. We provide a simple scheme by which these errors may be corrected.