A quantum embedding theory in the screened Coulomb interaction: Combining configuration interaction with GW/BSE

TL;DR

The paper introduces a new quantum embedding method called DCI that combines wave function and Green's function theories to accurately treat static and dynamic correlations in molecules, showing excellent agreement with experiments.

Contribution

The paper presents the dynamical configuration interaction (DCI) theory, a novel embedding approach that unifies wave function and Green's function methods for improved electronic structure calculations.

Findings

Accurately predicts dissociation curves and excitation energies.

Treats ground and excited states on equal footing.

Achieves excellent agreement with high-level methods and experiments.

Abstract

We present a new quantum embedding theory called dynamical configuration interaction (DCI) that combines wave function and Green's function theories. DCI captures static correlation in a correlated subspace with configuration interaction and couples to high-energy, dynamic correlation outside the subspace with many-body perturbation theory based on Green's functions. In the correlated subspace, we use a wave function description to avoid embedding the two-particle vertex, which greatly simplifies the frequency structure of the embedding. DCI takes the strengths of both theories to balance static and dynamic correlation in a single, fully ab-initio embedding concept. We show that treating high-energy correlation up to the $GW$ and Bethe-Salpeter equation level is sufficient even for challenging multi-reference problems. Our theory treats ground and excited states on equal footing, and we compute the dissociation curve of N$_2$, vertical excitation energies of N$_2$ and C$_2$, and the ionization spectrum of benzene in excellent agreement with high level quantum chemistry methods and experiment.