Theory can provide important support at all the stages of spectroscopic experiments, from planning the measurements, through extracting the properties of interest from the data, and to the interpretation of the results and their comparison to predicted values. This support is especially important for experiments on the heaviest elements, which are challenging due to the short lifetimes and the low quantities of the investigated species. To provide useful predictions, highly accurate calculations of atomic properties are needed. In order to be reliable, such calculations must include both relativistic effects and electron correlation on the highest possible level. Relativistic coupled cluster is considered one of the most powerful methods for accurate treatment of these effects and for calculations of properties of heavy elements. One of the advantages of this approach is that it allows us to set an uncertainty on the calculated results, facilitating their use in experimental research.

A brief introduction to the relativistic coupled cluster method will be provided in the talk, including the recently developed scheme for uncertainty evaluation. In the rest of the presentation I will focus on the recent successful applications of the coupled cluster approach to spectra, hyperfine structure, and other properties of the heaviest elements.