Relativistic quantum mechanical methods in molecular calculations

In the present paper the theory for different relativistic methods is presented. Despite a lot of progress has been made for the inclusion of relativistic effects in electronic structure calculations, good methods are still resource‐demanding. A rapid development of the four‐component method is, however, taking place. Also, “pseudo‐relativistic” approaches are becoming more popular in the treatment of large systems. The importance of the interplay between the relativistic core and valence effects is also revisited.