Electronic transport in molecular junctions: The generalized Kadanoff-Baym ansatz with initial contact and correlations

TL;DR

This paper develops an extended generalized Kadanoff-Baym ansatz (GKBA) method that incorporates initial correlations in quantum transport simulations of molecular junctions, enabling more accurate modeling of transient currents.

Contribution

The authors introduce a GKBA scheme that includes initial correlations in a partition-free setting, improving the simulation of contacted molecular junctions without increasing computational complexity.

Findings

The method accurately captures the role of electron correlations in transient current signatures.

The approach allows separation of equilibration from real-time evolution in simulations.

Application to carbon-based junctions demonstrates the importance of initial correlations.

Abstract

The generalized Kadanoff-Baym ansatz (GKBA) offers a computationally inexpensive approach to simulate out-of-equilibrium quantum systems within the framework of nonequilibrium Green's functions. For finite systems the limitation of neglecting initial correlations in the conventional GKBA approach has recently been overcome [Phys. Rev. B 98, 115148 (2018)]. However, in the context of quantum transport the contacted nature of the initial state, i.e., a junction connected to bulk leads, requires a further extension of the GKBA approach. In this work, we lay down a GKBA scheme which includes initial correlations in a partition-free setting. In practice, this means that the equilibration of the initially correlated and contacted molecular junction can be separated from the real-time evolution. The information about the contacted initial state is included in the out-of-equilibrium calculation via explicit evaluation of the memory integral for the embedding self-energy, which can be performed without affecting the computational scaling with the simulation time and system size. We demonstrate the developed method in carbon-based molecular junctions, where we study the role of electron correlations in transient current signatures.