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

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 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 CC with
singles and doubles (CCSD) to CC with singles, doubles, and triples
(CCSDT) or from CCSDT to CC with singles, doubles, triples, and quadruples
(CCSDTQ)) reduces the average error with respect to the near-FCI reference
values by approximately 1 order of magnitude.