Quantum Embedding Theory for Strongly-correlated States in Materials

TL;DR

This paper introduces a quantum embedding theory for strongly-correlated electronic states, utilizing effective Hamiltonians and density functional theory, avoiding the need for the random phase approximation, and demonstrating its application to spin defects in semiconductors.

Contribution

The paper provides a detailed derivation of a novel quantum embedding theory based on effective Hamiltonians, extending it to non-eigenstate orbitals, and applying it to real material systems.

Findings

Effective Hamiltonian approach for strongly-correlated states

Circumvents virtual orbital calculations using existing algorithms

Demonstrates application to spin defects in semiconductors

Abstract

Quantum embedding theories are promising approaches to investigate strongly-correlated electronic states of active regions of large-scale molecular or condensed systems. Notable examples are spin defects in semiconductors and insulators. We present a detailed derivation of a quantum embedding theory recently introduced, which is based on the definition of effective Hamiltonians. The effect of the environment on a chosen active space is accounted for through screened Coulomb interactions evaluated using density functional theory. Importantly, the random phase approximation is not required and the evaluation of virtual electronic orbitals is circumvented with algorithms previously developed in the context of calculations based on many-body perturbation theory. In addition, we generalize the quantum embedding theory to active spaces composed of orbitals that are not eigenstates of Kohn-Sham Hamiltonians. Finally, we report results for spin defects in semiconductors.