Relativistic Effects on Molecular Properties

In chemical research, there is a pressing need to be able to calculate and rationalize molecular electric, magnetic, optical, and spectroscopic properties. For heavy element systems, relativistic effects on such properties can become very large. For high-accuracy calculations, relativistic effects are needed even for the lightest elements. The theoretical background for relativistic quantum chemical calculations of molecular properties is reviewed, along with a variety of examples showcasing relativistic effects on atomic shell properties, bond lengths and binding energies, magnetic resonance parameters, electric and magnetic properties, the electron density, and spin-forbidden processes enabled by spin-orbit coupling.