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This study compares results of four relativistic pseudopotential basis sets, which differ mainly by their size: double‐zeta introduced by Hay and Wadt from Los Alamos National Laboratory (LANL2DZ), triple‐zeta based on Stuttgart energy‐consistent scalar‐relativistic pseudopotential (SDD3), its extension with 2fg polarization functions, and combination of Stuttgart pseudopotentials with quintuple‐zeta cc‐pV5Z base (SDD5). Hydrides of transition metals from Cr to Zn group are chosen as reference molecules. The coupled cluster method (CCSD(T)) is used for evaluation of selected molecular characteristics. Interatomic distances, dissociation energies, vibration modes, and anharmonicity constants are determined and compared with available experimental data. As expected, the accuracy of basis depends mainly on its size. However, only moderate modification of SDD3 basis set significantly improves its accuracy, which becomes comparable to the largest basis set. Nevertheless, the time consumption is significantly lower. [ABSTRACT FROM AUTHOR]

Electronic excited states in the series of polyene molecules were explored. Optimal ground‐state geometry was used for the evaluation of vertical excitation energies. Results of a chosen set of functionals were compared to post‐HF methods (EOM‐CCSD, NEVPT2, CASPT2, and MRCI). In addition, the semiempirical OM2/MNDO method using MRCISD computational level was confronted with the above‐mentioned techniques. Despite the fact that the first excited state has a significant double‐excitation character some functionals were able to qualitatively determine the correct state order (where the lowest excited state has a Ag− character). The most successful functionals in transition energies predictions were PBE, TPSS and BLYP in Tamm‐Dancoff approach (TDA), which had the smallest root‐mean‐square deviation (RMSD) scoring towards the experimental values. Regarding RMSD scoring, the OM2/MNDO method performed fairly well, too. Besides absorption spectra, lifetimes of the first two excited states were estimated based on a stochastic approach exploring a swarm of OM2/MNDO hopping dynamics using the Tully fewest switch algorithm for each molecule. The longest lifetime of the first excited state (S1) was found for decapentaene (about 5 ps). Further elongation of the conjugated chain caused a mild decrease of this value to ca 1.5 ps for docosaundecaene. [ABSTRACT FROM AUTHOR]