Relativistic quantum mechanical methods in molecular calculations

Abstract 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 fourcomponent 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.