An Introduction to Relativistic Quantum Chemistry

Chemistry is governed by the shell structure of the atoms. This holds in particular concerning the periodic system of chemical elements. Non-relativistic quantum chemistry describes the motion of electrons and nuclei and their mutual interactions to a first approximation. It reproduces a large fraction of chemistry of the more important lighter elements sufficiently well. A significant amount of chemical insight can already be gained from the analysis of the atomic one-electron orbitals. However, while valence electrons have ‘non-relativistically small’ energies, they become ‘relativistically fast’ in the neighborhood of heavy nuclei. The importance of relativistic effects in the atomic valence shells increases approximately as Z2. Relativity significantly changes the chemical trends at the bottom of the periodic table. The relativistic effects of the valence electrons can be classified as direct and indirect ones. The direct ones are due to the increase of the effective mass with velocity, to the change of the electric nuclear attraction of a spinning electron, and to the magnetic spin-orbit coupling. The indirect effects on the valence electrons are due to the relativistic changes of nuclear shielding and Pauli repulsion by the inner orbitals. The changes of the radial, the angular, and the quaternionic phase behavior of the relativistic atomic valence orbitals modify the atomic bonding properties, the energetics, the structure and properties of the molecules.