Strongly correlated states of transition metal spin defects: the case of an iron impurity in aluminum nitride

TL;DR

This paper explores the electronic structure of iron impurities in aluminum nitride using advanced embedding methods and TDDFT, providing insights into strongly correlated defect states relevant for quantum technologies.

Contribution

It demonstrates the effectiveness of DMET and QDET in accurately modeling defect states and establishes a protocol for converged, experimentally comparable results.

Findings

DMET and QDET accurately describe ground and excited states

TDDFT reproduces experimental photoluminescence spectra

Convergence protocol for embedding calculations

Abstract

We investigate the electronic properties of an exemplar transition metal impurity in an insulator, with the goal of accurately describing strongly correlated, defect states. We consider iron in aluminum nitride, a material of interest for hybrid quantum technologies, and we carry out calculations with quantum embedding methods -- density matrix embedding theory (DMET) and quantum defect embedding theory (QDET) and with spin-flip time-dependent density functional theory (TDDFT). We show that both DMET and QDET accurately describe the ground state and low-lying excited states of the defect, and that TDDFT yields photoluminescence spectra in agreement with experiments. In addition, we provide a detailed discussion of the convergence of our results as a function of the active space used in the embedding methods, thus defining a protocol to obtain converged data, directly comparable with experiments.