Multi-orbital Non-Crossing Approximation from maximally localized Wannier functions: the Kondo signature of copper phthalocyanine on Ag (100)

TL;DR

This paper introduces a multi-orbital non-crossing approximation method using maximally localized Wannier functions to analyze the Kondo effect in a copper phthalocyanine molecule on Ag (100), highlighting limitations of standard DFT.

Contribution

The authors develop a novel approach combining DFT and non-crossing approximation with Wannier functions to study the Kondo effect in complex molecular systems.

Findings

Successfully modeled spectral functions for different spin configurations.

Identified limitations of standard DFT in handling open-shell molecules on surfaces.

Demonstrated the method's applicability to real molecular systems.

Abstract

We have developed a multi-orbital approach to compute the electronic structure of a quantum impurity using the non-crossing approximation. The calculation starts with a mean-field evaluation of the system's electronic structure using a standard quantum chemistry code. Here we use density functional theory (DFT). We transformed the one-electron structure into an impurity Hamiltonian by using maximally localized Wannier functions (MLWF). Hence, we have developed a method to study the Kondo effect in systems based on an initial one-electron calculation. We have applied our methodology to a copper phthalocyanine molecule chemisorbed on Ag (100), and we have described its spectral function for three different cases where the molecule presents a single spin or two spins with ferro- and anti-ferromagnetic exchange couplings. We find that the use of broken-symmetry mean-field theories such as Kohn-Sham DFT cannot deal with the complexity of the spin of open-shell molecules on metal surfaces and extra modeling is needed.