Application of relativistic theories and quantum electrodynamics to chemical problems

The BERTHA program embodies a new formulation of relativistic molecular str ucture theory within the framework of relativistic quantum electrodynamics (QED). This leads to a simple and transparent formulation of Dirac-Hartree- Fock-Breit (DHFB) self-consistent field equations along with algorithms for molecular properties, electron correlation, and higher order QED effects. The DHFB equations are solved by a direct method based on a relativistic ge neralization of the McMurchie-Davidson algorithm for molecular integrals th at economizes memory requirements and is not significantly more expensive c omputationally than comparable nonrelativistic calculations. Some noteworth y features of this approach; include the ease with which relativistic point -group symmetry can be analyzed and the ease of calculation of electromagne tic properties, for example, g factors, nuclear hyperfine interactions, nuc lear magnetic resonance (NMR) shielding parameters and molecular effects of parity-violating weak interactions. The "negative energy" states, which ar e often regarded as a dangerous nuisance in other treatments of relativisti c effects, make a vital contribution. As well as outlining the main ideas u nderlying our development, this study presents results for small molecules, some of which involve heavy elements. (C) 2000 John Wiley & Sons, Inc.