Heinz Siedentop, Edgardo Stockmeyer
The Douglas-Kroll-He{\ss} Method: Convergence and Block-Diagonalization of Dirac Operators
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ABSTRACT.  We show that the Douglas-Kroll block-diagonalization method for the 
Dirac operator with Coulomb potential is convergent in norm 
resolvent sense for coupling constant $\gamma$ less than 
$\gamma_c=0.37758$ which corresponds to atomic number $51$. 
Moreover, we give an explicit expression for the corresponding 
block-diagonalized Dirac operator.