Quantitative evaluation of TD-DFT functionals for UV-vis spectroscopy in Ni and Co complexes

This work presents a systematic benchmark of time-dependent density functional theory (TD-DFT) methodologies for predicting the ultraviolet-visible (UV-vis) absorption spectra of mononuclear nickel and cobalt coordination complexes. For this purpose, 20 nickel and 15 cobalt structurally diverse coordination complexes with experimental UV-vis spectra available were selected from the literature. All structures were optimized at the DFT/TPSSh(D4)/def2-TZVP/C-PCM(solvent) level of theory and TD-DFT calculations were made employing 18 functionals (BP86, OPBE, PBE, r²SCAN revM06-L, TPSS, B3LYP/G, B97, BH&HLYP, M06, M06-2X, O3LYP, PBE0, TPSSh, CAM-B3LYP, ωB97X, ωPBE and PWPB95). The functionals were ranked according to their effectiveness in reproducing both the excitation energies and the overall spectral shape observed experimentally, incorporating Gaussian broadening for bandwidth adjustment and applying energy shift corrections to the calculated transitions. For Ni compounds, the hybrid functional TPSSh yield the most accurate excitation energies while the also hybrid functional BH&HLYP demonstrated the best perfomance for reproducing the spectral shape, having a high average similarity to the experimental data in cost of a high average absolute shift value. For Co compounds, the best performer for both excitation energies and spectral shape was the hybrid PBE0 functional by using the same criteria.