A Mountaineering Strategy to Excited States: Highly-Accurate Energies and Benchmarks for Exotic Molecules and Radicals
Abstract
Aiming at completing the sets of FCI-quality transition energies that we recently developed (J.~Chem.~Theory Comput. 14 (2018) 4360--4379, ibid.~15 (2019) 1939--1956, and ibid.~16 (2020) 1711--1741), we provide, in the present contribution, ultra-accurate vertical excitation energies for a series of "exotic" closed-shell molecules containing F, Cl, P, and Si atoms and small radicals, such as CON and its variants, that were not considered to date in such investigations. This represents a total of 81 high-quality transitions obtained with a series of diffuse-containing basis sets of various sizes. For the exotic compounds, these transitions are used to perform benchmarks with a vast array of lower-level models, i.e. CIS(D), EOM-MP2, (SOS/SCS)-CC2, STEOM-CCSD, CCSD, CCSDR(3), CCSDT-3, (SOS-)ADC(2), and ADC(3). Additional comparisons are made with literature data. For the open-shell compounds, we have compared the performances of both the unrestricted and restricted open-shell CCSD and CC3 formalisms.