Multi-Space Excitation as an Alternative to the Landauer Picture for Nonequilibrium Quantum Transport.

Juho Lee,Yong-Hoon Kim,Han Seul Kim

doi:10.1002/advs.202001038

Abstract

While the Landauer viewpoint constitutes a modern basis to understand nanoscale electronic transport and to realize first‐principles implementations of the nonequilibrium Green's function (NEGF) formalism, seeking an alternative picture can be beneficial for the fundamental understanding and practical calculations of quantum transport processes. Herein, introducing a micro‐canonical picture that maps the finite‐bias quantum transport process to a drain‐to‐source or multi‐electrode optical excitation, the multi‐space constrained‐search density functional theory (MS‐DFT) formalism for first‐principles electronic structure and quantum transport calculations is developed. Performing MS‐DFT calculations for the benzenedithiolate single‐molecule junction, it is shown that MS‐DFT and standard DFT‐NEGF calculations produce practically equivalent electronic and transmission data. Importantly, the variational convergence of “nonequilibrium total energy” within MS‐DFT is demonstrated, which should have significant implications for in operando studies of nanoscale devices. Establishing a viable alternative to the Landauer viewpoint, the developed formalism should provide valuable atomistic information in the development of next‐generation nanodevices.

Highlights

Density functional theory (DFT) in the standard form cannot be applied to non-equilibrium quantum electron transport phenomena, in the last decade or so the method combining DFT and non-equilibrium Green’s function (NEGF) formalism within the Landauer viewpoint has been established as the standard approach for first-principles finite-bias quantum transport calculations.[1, 2]
We find that the linear electrostatic potential drop profile across the molecule obtained from DFT-NEGF is accurately reproduced by multi-space constrained-search density functional theory (MS-DFT), confirming the practical equivalence between the two approaches
The resulting MS-DFT method provides an alternative route to the standard DFT-NEGF scheme for ab initio non-equilibrium electronic structure and quantum transport calculations and was straightforwardly implemented within a standard DFT code

Summary

INTRODUCTION

Density functional theory (DFT) in the standard form cannot be applied to non-equilibrium quantum electron transport phenomena, in the last decade or so the method combining DFT and non-equilibrium Green’s function (NEGF) formalism within the Landauer viewpoint has been established as the standard approach for first-principles finite-bias quantum transport calculations.[1, 2] While successful, the DFTNEGF approach suffers from several shortcomings due to the Landauer framework invoked in its numerical realization. Regarding our initial report on the development of MS-DFT,[9] concern was raised on its validity in that we demonstrated its equivalence with DFT-NEGF only for the vertically-stacked two-dimensional systems involving weak van der Waals interactions. In this and accompanying articles,[10] taking the more established molecular junctions that involve covalent bonding between molecules and electrodes, we show that the quantum transport properties calculated within the standard DFT-NEGF method are faithfully reproduced by the MS-DFT approach. The variational convergence of the “non-equilibrium total energy” with respect to the basis-set level within MS-DFT will be demonstrated, which should have significant implications for the first-principles investigations of electrified interfaces for nano-electronic/energy/bio device applications

FORMULATION OF MS-DFT

IMPLEMENTATION OF MS-DFT

RESULTS AND DISCUSSION

CONCLUSION