Extended Douglas-Kroll transformation

Extended Douglas—Kroll transformations applied to the relativistic many-electron Hamiltonian... 

T. Nakajima, K. Hirao. Extended Douglas-Kroll transformations applied to the relativistic many-electron Hanrilto-nian. /. Chem. Phys., 119(8) (2003) 4105-4111. 

Molecules are more difficult to treat accurately than atoms, because of the reduced symmetry. An additional complication arises in relativistic calculations the Dirac-Fock-(-Breit) orbitals will in general be complex. One way to circumvent this difficulty is by the Douglas-Kroll-Hess transformation [57], which yields a one-component function with computational effort essentially equal to that of a nonrelativistic calculation. Spin-orbit interaction may then be added as a perturbation, implementation to AuH and Au2 has been reported [58]. Progress has also been made in the four-component formulation [59], and the MOLFDIR package [60] has been extended to include the CC method. Application to SnH4 has been described [61] here we present a recent calculation of several states of CdH and its ions [62], with one-, two-, and four-component methods. 

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