High-Level Coupled-Cluster Energetics by Merging Moment Expansions with Selected Configuration Interaction

TL;DR

This paper introduces a new coupled-cluster method that combines moment expansions with selected configuration interaction, replacing stochastic processes with CIPSI to efficiently approximate high-level energetics.

Contribution

The novel CIPSI-driven CC($P$;$Q$) approach replaces stochastic QMC with selected CI, enabling efficient high-accuracy energy calculations for complex molecules.

Findings

Accurately reproduces CC energies with fewer determinants.

Successfully applied to F2 dissociation and cyclobutadiene automerization.

Demonstrates efficiency and accuracy of the new method.

Abstract

Inspired by our earlier semi-stochastic work aimed at converging high-level coupled-cluster (CC) energetics [J. E. Deustua, J. Shen, and P. Piecuch, Phys. Rev. Lett. 119, 223003 (2017); J. Chem. Phys. 154, 124103 (2021)], we propose a novel form of the CC($P$;$Q$) theory in which the stochastic Quantum Monte Carlo propagations, used to identify dominant higher-than-doubly excited determinants, are replaced by the selected configuration interaction (CI) approach using the CIPSI algorithm. The advantages of the resulting CIPSI-driven CC($P$;$Q$) methodology are illustrated by a few molecular examples, including the dissociation of $\mathrm{F_2}$ and the automerization of cyclobutadiene, where we recover the electronic energies corresponding to the CC calculations with a full treatment of singles, doubles, and triples based on the information extracted from compact CI wave functions originating from relatively inexpensive Hamiltonian diagonalizations.