Exact ground state density functional theory for impurity models coupled to external reservoirs and transport calculations

TL;DR

This paper introduces a method combining density matrix renormalization group with density functional theory to accurately compute ground state properties and transport in impurity models coupled to reservoirs, highlighting the importance of exact functionals.

Contribution

It presents a novel approach to construct exact ground state exchange correlation functionals for impurity models using DMRG, improving transport calculation accuracy.

Findings

Transport resonances are reproduced almost exactly.

Level broadening deviations are less than 1% and do not exceed 10%.

Approximate ground state functionals can cause significant errors in transport predictions.

Abstract

A method is presented, which employs the density matrix renormalization group technique in order to construct exact ground state exchange correlation functionals for models of correlated electron systems coupled to external reservoirs. The technique is applied to the M-site resonant level model. We calculate its exact Kubo-conductance, which is available within DMRG, and compare to the single-particle conductance obtained from Kohn-Sham energies and orbitals of the exact ground state density functional theory (DFT). It is found that the position of transport resonances is reproduced essentially exactly, while deviations in the level broadening can be less than 1% and do not exceed 10%. Our findings lend strong support to a recently held point of view, namely that approximations in the ground state functionals used in DFT based transport calculations can lead to drastic errors in transport calculations while exchange correlation contributions to the induced effective potential tend to be less significant.