Other two-component Hamiltonians

This expression is obtained directly from the four-component DKS Hamiltonian, avoiding the free-particle Foldy-Wouthuysen transformation. After application 

The relativistic elimination of small components (RESC) is another two-component scheme that was applied to the DKS problem [69,102]. After transforming the DKS Hamiltonian in the same fashion as in the regular approximations [based on the generator X(e), Eq. (44)], the potential dependence of the relativistic terms is decomposed using the identity 

Then the potential and energy dependence are eliminated by substituting the relativistic kinetic energy Ep - mc for the difference - V in the arguments off and/ . Furthermore, one has to adjust the Hamiltonian to render it hermitean and to normalize the solutions [69,102]. The performance of the SR variant of the RESC method was demonstrated for the Ag and Au atoms, their hydrides and chlorides [69,102]. 

Recently, the accuracy of two-component Hamiltonians was analyzed in terms of [90,92], 

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