Introduction to Relativistic Electronic Structure Calculations

It is important to include relativistic effects in electronic structure calculations for many important chemical problems, including heavy-element chemistry, intersystem crossing, and zero-field splitting. The subject is old, but recent developments have been rapid. The specialized literature can be daunting for nonspecialists, and this article is intended to provide an entry to that literature, especially for the modern treatment of molecules. There are only five equations. We include discussion of the relations between four-component, two-component, and one-component treatments, the distinction between scalar relativistic effects and angular-momentum-dependent effects, approximate treatments of spin-orbit coupling, including the molecular mean-field approximations, the inclusion of electron correlation in relativistic wave functions, and zero-field splitting.