Chapter 14. Special Computational Techniques

Summary

In the preceding chapters we set out from fundamental physical theory to arrive at a suitable theory for calculations on atoms and molecules, which still features four-component one-particle states. However, we noted that not only for small nuclear charges the contribution of the lower components of these spinors are small indeed. Hence, attempts were made to find Hamiltonians which do not require lower components in the corresponding one-particle functions and which thus are more convenient from a conceptual and — if possible — from a computational point of view. The principal options for such an elimination of small components are now introduced.