On the performance of QTP functionals applied to second-order response properties

Correlated orbital theory (COT) is an exact one-particle treatment that adds essential electron correlation into its molecular orbitals, potentially reducing correlated treatments of response properties to one-particle coupled-perturbed Hartree-Fock- or Kohn-Sham-like calculations. Such a computation is vastly simpler than the usual ab initio correlated approach that would add correlation typically with EOM-CC after a perturbed mean-field solution. The question then is, how well can this be accomplished via the Quantum Theory Project (QTP) exchange-correlation (XC) functionals that are meant to emulate the rigorous COT framework? This paper addresses this question for response properties by making comparisons between such orbital-specific calculations and those from well-correlated EOM-CC solutions for static polarizabilities, nuclear magnetic resonance coupling constants, and chemical shifts. The simple orbital-specific version provides an accurate realization of the correlated EOM-CC results, but now in a mode that facilitates an orbital-by-orbital interpretation. Here, we compare 33 XC functionals from the different Jacob’s ladder rungs always against the EOM-CCSD results. Thus, the smallest mean absolute deviation for the static polarizability comes from LC-QTP XC, 0.28 a.u. Regarding the total nuclear spin-spin coupling constants, QTP01 performs best, %Error = 10.63% (QTP02 and LC-QTP are second and third best). Finally, the XC that stood out in the chemical shift analysis was TPSS0, which presented the best result for the majority of the chemical shifts. However, considering the overall performances based on linear fitting of all isotope data points, five functionals are recommended for a chemical shift study: TPSS0, ωB97X, QTP00, QTP01, and QTP02, all presenting R² = 0.96.