Choosing an atomic basis set for TD-DFT, SOPPA, ADC(2), CIS(D), CC2 and EOM-CCSD calculations of low-lying excited states of organic dyes

Aiming to pinpoint an atomic basis set providing accurate transition energies at a minimal computational cost, we investigate the evolution with basis set size of the energy of low-lying excited states in nine representative conjugated dyes with a wide panel of theoretical approaches, namely TD-DFT, SOPPA, ADC(2), CIS(D), CC2, EOM-CCSD, as well as several scaled opposite spin variants, namely SOS-CIS(D), SOS-CIS(D0) and SOS-ADC(2). At the exception of TD-DFT that displays the lowest basis set dependence, it turns out that the changes obtained when increasing the size of the basis set are rather independent of the selected wavefunction model, but strongly change according to the nature of the excited state considered. Reasonable compromises between accuracy and computational burden can be attained with 6-311+G(2d,p) that allows much faster calculations than the typical reference basis set, namely aug-cc-pVTZ, for an average loss of accuracy limited to ca. 0.02 eV.