Extension of the Active-Orbital-Based and Adaptive CC($P$;$Q$) Approaches to Excited Electronic States: Application to Potential Cuts of Water

TL;DR

This paper introduces active-orbital-based and adaptive CC(P;Q) methods for excited states, demonstrating their accuracy and efficiency in modeling water's O-H bond-breaking potential compared to full CCSDT/EOMCCSDT calculations.

Contribution

It extends CC(P;Q) approaches to excited states and applies them to water, showing improved accuracy and reduced computational cost over traditional methods.

Findings

Active-orbital-based and adaptive CC(P;Q) closely match CCSDT/EOMCCSDT results.

These methods improve energetics in stretched bond regions.

Significant computational savings achieved.

Abstract

We report the first study using active-orbital-based and adaptive CC($P$;$Q$) approaches to describe excited electronic states. These CC($P$;$Q$) methodologies are applied, alongside their completely renormalized (CR) coupled-cluster (CC) and equation-of-motion (EOM) CC counterparts, to recover the ground- and excited-state potential cuts of the water molecule along the O-H bond-breaking coordinate obtained in the parent CC/EOMCC calculations with a full treatment of singles, doubles, and triples (CCSDT/EOMCCSDT). We demonstrate that the active-orbital-based and adaptive CC($P$;$Q$) approaches closely approximate the CCSDT/EOMCCSDT data using significantly reduced computational costs while improving the CR-CC and CR-EOMCC energetics in stretched regions of the O-H bond-breaking potentials.