A coupled cluster framework for electrons and phonons

TL;DR

This paper develops a coupled cluster computational framework for electrons and phonons, enabling the study of their interactions in materials, with benchmarks and initial applications to solids and finite models.

Contribution

It introduces a coupled cluster approach for electron-phonon systems, including equation-of-motion methods and implementation details for ab initio calculations.

Findings

Benchmarks on Hubbard-Holstein model show good performance for weak to moderate coupling.

Progress towards ab initio calculations on solids demonstrated with preliminary diamond results.

Implementation of electron-phonon matrix elements in PySCF enhances computational capabilities.

Abstract

We describe a coupled cluster framework for coupled systems of electrons and phonons. Neutral and charged excitations are accessed via the equation-of-motion version of the theory. Benchmarks on the Hubbard-Holstein model allow us to assess the strengths and weaknesses of different coupled cluster approximations which generally perform well for weak to moderate coupling. Finally, we report progress towards an implementation for {\it ab initio} calculations on solids, and present some preliminary results on finite-size models of diamond. We also report the implementation of electron-phonon coupling matrix elements from crystalline Gaussian type orbitals (cGTO) within the PySCF program package.