Application of relativistic theories and quantum electrodynamics to chemical problems

Abstract

The BERTHA program embodies a new formulation of relativistic molecular structure 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 generalization of the McMurchie–Davidson algorithm for molecular integrals that economizes memory requirements and is not significantly more expensive computationally than comparable nonrelativistic calculations. Some noteworthy features of this approach include the ease with which relativistic point-group symmetry can be analyzed and the ease of calculation of electromagnetic properties, for example, g factors, nuclear hyperfine interactions, nuclear magnetic resonance (NMR) shielding parameters and molecular effects of parity-violating weak interactions. The “negative energy” states, which are often regarded as a dangerous nuisance in other treatments of relativistic effects, make a vital contribution. As well as outlining the main ideas underlying our development, this study presents results for small molecules, some of which involve heavy elements. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 80: 283–297, 2000