Effective bias and potentials in steady-state quantum transport: A NEGF reverse-engineering study

TL;DR

This study investigates how effective bias and potentials in steady-state quantum transport are influenced by interactions and system size, using a reverse-engineering approach to improve density-functional-theory methods.

Contribution

It introduces a reverse-engineering procedure to determine effective potentials and biases in quantum transport, highlighting their dependence on interactions and system length.

Findings

Effective bias depends strongly on interaction strength.

Effective bias varies with the length of the central region.

Sensitivity of effective bias to many-body approximation levels.

Abstract

Using non-equilibrium Green's functions combined with many-body perturbation theory, we have calculated steady-state densities and currents through short interacting chains subject to a finite electric bias. By using a steady-state reverse-engineering procedure, the effective potential and bias which reproduce such densities and currents in a non-interacting system have been determined. The role of the effective bias is characterised with the aid of the so-called exchange-correlation bias, recently introduced in a steady-state density-functional-theory formulation for partitioned systems. We find that the effective bias (or, equivalently, the exchange-correlation bias) depends strongly on the interaction strength and the length of the central (chain) region. Moreover, it is rather sensitive to the level of many-body approximation used. Our study shows the importance of the effective/exchange-correlation bias out of equilibrium, thereby offering hints on how to improve the description of density-functional-theory based approaches to quantum transport.