Excited-State Polarizabilities: CC3 Reference Values,Wavefunction and TD-DFT Benchmarks

We present a comprehensive benchmark of excited-states polarizabilities for a representative set of 41 singlet states from 27 small organic molecules. Reference data were obtained using the high-level coupled-cluster CC3 model in combination with the aug-cc-pVTZ atomic basis set, providing the first systematic dataset of e0xcited-state polarizabilities at this level of theory. The studied set includes both valence and Rydberg states, the latter exhibiting significantly larger polarizabilities, reflecting their diffuse character and enhanced sensitivity to external electric fields. The benchmark analysis includes lower-order wavefunction-based methods, namely CCSD and CC2, as well as Time-Dependent Density Functional Theory (TD-DFT) with several common density functional approximations (B3LYP, MN15, M06-2X, CAM-B3LYP, and LC-BLYP). The statistical analysis enables the evaluation of the impact of orbital relaxation and highlights method-dependent differences across the different kind of excited states, as well as according to the different chemical character of molecules. The results indicate that CCSD, both in its relaxed and unrelaxed forms, provides the most accurate description of excited-state polarizabilities, closely followed by CC2, which can therefore be generally employed as a computationally efficient yet reliable alternative. Among the TD-DFT functionals, range-separated hybrids – particularly LC-BLYP – perform best, while larger errors are observed for the three evaluated global hybrids.