Extension of the CIPSI-Driven CC($P$;$Q$) Approach to Excited Electronic States

TL;DR

This paper extends the CIPSI-driven CC($P$;$Q$) method to excited states using EOM-CC formalism, demonstrating efficient convergence of excitation energies with smaller CI spaces across various molecules.

Contribution

The authors adapt the CIPSI-driven CC($P$;$Q$) approach for excited states within the EOM-CC framework, enabling accurate results with reduced computational cost.

Findings

Converges excitation energies from smaller CI spaces.

Effective for vertical and adiabatic excitations in molecules.

Reduces computational expense compared to traditional methods.

Abstract

We extend the CIPSI-driven CC($P$;$Q$) methodology [K. Gururangan et al., J. Chem. Phys. 155 (2021) 174114], in which the leading higher-than-doubly excited determinants are identified using the selected configuration interaction (CI) approach abbreviated as CIPSI, to excited electronic states via the equation-of-motion (EOM) coupled-cluster (CC) formalism. By examining vertical excitations in CH+ at equilibrium and stretched geometries, adiabatic excitations in CH, and ground- and excited-state potential cuts of water, we demonstrate that the CIPSI-driven CC($P$;$Q$) method converges parent CC/EOMCC singles, doubles, and triples energetics from relatively inexpensive Hamiltonian diagonalizations in CI spaces smaller than the corresponding triples manifolds.