The identification of signatures of heavy elements synthesized in the ejecta of two merging neutron stars requires the modelling of the electromagnetic signal following the merger, called kilonova. In order to reproduce these spectral features, corresponding radiative transfer models require input on the atomic transitions between bound states for ions of the first few ionization stages. Due to the complex electronic structures of the lanthanides and actinides in particular, experimental data is limited for heavy elements and the theoretical computation of atomic datasets involves a tradeoff between completeness and computation time. For the radiative transfer models, the datasets have to include all relevant transitions. We perform atomic structure calculations with different sets of electronic configurations and investigate the convergence of state densities and expansion opacities.