Accurate full configuration interaction correlation energy estimates for five- and six-membered rings

Following our recent work on the benzene molecule [P.-F. Loos, Y. Damour, and A. Scemama, J. Chem. Phys. 153, 176101 (2020)], motivated by blind challenge of Eriksen et al. [J. Lett. 11, 8922 (2020)] same system, we report accurate full configuration interaction (FCI) frozen-core correlation energy estimates for 12 five- six-membered ring molecules (cyclopentadiene, furan, imidazole, pyrrole, thiophene, benzene, pyrazine, pyridazine, pyridine, pyrimidine, s-tetrazine, s-triazine) in standard correlation-consistent double-? Dunning basis set (cc-pVDZ). Our FCI estimates, with an estimated error smaller than 1 millihartree, are based energetically optimized-orbital selected calculations performed using a perturbative selection made iteratively algorithm. Having at disposal these reference energies, respective performance convergence properties several popular widely used families single-reference quantum chemistry methods investigated. In particular, study (i) Møller–Plesset perturbation series up to fifth-order (MP2, MP3, MP4, MP5), (ii) iterative approximate coupled-cluster CC2, CC3, CC4, (iii) CCSD, CCSDT, CCSDTQ. The ground-state gold CCSD(T) as well completely renormalized CC model, CR-CC(2,3), is also We show that MP4 provides interesting accuracy/cost ratio, while MP5 systematically worsens estimates. addition, CC3 outperforms its more expensive parent CCSDT. A similar trend observed including quadruple excitations, where CC4 model shown be slightly CCSDTQ, both providing energies within 2 millihartree limit.