Relation of Large and Small Components in One-Electron Equations

Relation of Large and Small Components in One-Electron Equations 

Although accurate, first-quantized four-component methods are both computationally demanding and plagued by interpretive problems due to the negative-energy states. From a conceptual point of view it is desirable to decouple the upper and lower components of the Dirac Hamiltonian and to obtain a two-component description for electrons only. 

For this purpose, we focus on one-electron operators only, because even the first-quantized many-electron theory reduces to Dirac-like one-electron equations, i.e., to the self-consistent field equations. The Dirac Hamiltonian is then substituted by the four-dimensional Fock operator 

Relativistic Quantum Chemistry. Markus Reiher and Alexander Wolf 

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