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

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 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.

Approximate Excited-State Geometry Optimization with the State-Averaged Adaptive Sampling Configuration Interaction Algorithm with Large Active Spaces

“…The CI derivatives are (35) With these source terms, the Z-vector equation for ASCI-SCF is solved to obtain the effective densities as (36) (37) (38) where (39) (40)…”

“…Indeed, the first implementation of ASCI showed that the excited state is well described . Recently, the dipole moments and oscillator strengths are shown to be reliably described with the configuration interaction using a perturbative selection made iteratively (CIPSI) method . Naturally, if the ASCI formalism accurately approximates the FCI excited states, then the state-averaged ASCI-SCF (SA-ASCI-SCF) should resemble the SA-CASSCF states as well.…”

Generalization of the Tensor Product Selected CI Method for Molecular Excited States

“…Selected configuration interaction (SCI) 19 -based approaches have been recently used to calculate accurate estimates for vertical excitation energies, 20−23 double excitations, 13 doublet− doublet transitions in radicals, 24 and excited-state dipole moments and oscillator strengths. 25 relatively small subspace of determinants, SCI techniques attempt a bottom-up discovery of this space of "important" Slater determinants. For weakly correlated systems, SCI provides an incredibly efficient approach for obtaining near-FCI estimates of the ground and excitated state energies.…”

“…Selected configuration interaction (SCI)-based approaches have been recently used to calculate accurate estimates for vertical excitation energies, – double excitations, doublet–doublet transitions in radicals, and excited-state dipole moments and oscillator strengths . Motivated by the fact that low-energy eigenstates often have most of their weight on a relatively small subspace of determinants, SCI techniques attempt a bottom-up discovery of this space of “important” Slater determinants.…”

Analytic Non-adiabatic Couplings for Selected Configuration Interaction via Approximate Degenerate Coupled Perturbed Hartree–Fock

“…It does not require an active space to be chosen, so it removes the requirement of expertise and the possibility of bias. Selected CI initially used perturbation estimates of a configuration’s significance, and recently, there has been much successful research into going beyond this approach, which includes refs – . Those works have demonstrated that selected CI can be particularly useful for multireference problems, where small corrections to a single determinant can perform poorly.…”