Ground- and Excited-State Dipole Moments and Oscillator Strengths of Full Configuration Interaction Quality

TL;DR

This paper provides highly accurate FCI-quality calculations of dipole moments and oscillator strengths for small molecules, enabling assessment of high-order coupled-cluster methods' accuracy.

Contribution

It introduces near-FCI estimates using CIPSI to evaluate and compare the accuracy of advanced coupled-cluster methods for molecular properties.

Findings

Incrementing CC excitation levels significantly reduces errors.

Near-FCI estimates serve as benchmarks for high-order CC methods.

High-order CC methods approach FCI accuracy for molecular properties.

Abstract

We report ground- and excited-state dipole moments and oscillator strengths (computed in different ``gauges'' or representations) of full configuration interaction (FCI) quality using the selected configuration interaction method known as \textit{Configuration Interaction using a Perturbative Selection made Iteratively} (CIPSI). Thanks to a set encompassing 35 ground- and excited-state properties computed in 11 small molecules, the present near-FCI estimates allow us to assess the accuracy of high-order coupled-cluster (CC) calculations including up to quadruple excitations. In particular, we show that incrementing the excitation degree of the CC expansion (from CCSD to CCSDT or from CCSDT to CCSDTQ) reduces the average error with respect to the near-FCI reference values by approximately one order of magnitude.