# Coupled-cluster impurity solvers for dynamical mean-field theory

## TL;DR

This paper introduces coupled-cluster theory as an impurity solver in dynamical mean-field theory, demonstrating its accuracy and computational efficiency for Hubbard models and potential in ab initio applications.

## Contribution

It presents the use of coupled-cluster singles and doubles (CCSD) as an impurity solver in DMFT, enabling accurate results with many bath sites at low computational cost.

## Key findings

- CCSD accurately reproduces density of states and self-energies.
- Convergence achieved with approximately 30 bath sites per impurity.
- Large 4-site cluster DMFT with 120 bath sites successfully performed.

## Abstract

We describe the use of coupled-cluster theory as an impurity solver in dynamical mean-field theory (DMFT) and its cluster extensions. We present numerical results at the level of coupled-cluster theory with single and double excitations (CCSD) for the density of states and self-energies of cluster impurity problems in the one- and two-dimensional Hubbard models. Comparison to exact diagonalization shows that CCSD produces accurate density of states and self-energies at a variety of values of $U/t$ and filling fractions. However, the low cost allows for the use of many bath sites, which we define by a discretization of the hybridization directly on the real frequency axis. We observe convergence of dynamical quantities using approximately 30 bath sites per impurity site, with our largest 4-site cluster DMFT calculation using 120 bath sites. We suggest coupled cluster impurity solvers will be attractive in ab initio formulations of dynamical mean-field theory.