BERTHA and PyBERTHA: State of the art for full four-component Dirac-kohn-sham calculations

While since mid-seventies it has been clearly shown that relativistic effects play a crucial role for the complete understanding of the chemistry of molecules especially when heavy elements are involved, still nowadays in most of the case the relativistic effects are introduced via approximate methods. The main motivation behind the introduction of such approximation, respect to the natural and most rigorous component (4c) formalism derived from the Dirac equation, is the computational burden. In the present paper we are proposing a review of the BERTHA code that, together with the recently introduced Python bindings, represents the state of the art for full 4c calculations both in term of performances as well as in terms of code usability.