Molecular systems nonrelativistic/relativistic cases

At the moment the number of true four-component molecular EFG calculations is still rather limited due to the considerable computational effort especially in the post-DHF steps. Just five years ago Pj kko expressed the need for fully relativistic benchmark calculations in order to abandon perturbative corrections for considerable relativistic effects and to establish reference results. Furthermore spin-orbit effects can cause an EFG e.g. in atoms with Z > 0 and half-filled shells where according to nonrelativistic theory the EFG should vanish. This is the case for e.g. a system leading to a Pij2P f2 spin-orbit-split configuration. Also in closed-shell molecules with heavy halogen nuclei the spin-orbit effect is not completely quenched [88]. 

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