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SHAPE-CONSISTENT RELATIVISTIC EFFECTIVE POTENTIALS OF SMALL ATOMIC CORES

Relativistic effective core potential (RECP) models for electronic structure calculations of atoms, molecules, clusters, and solids, satisfying the shape-consistence (norm conservation) requirement are presented and analyzed. To attain a high accuracy of predicting various physical properties with field-independent RECP models, both valence and subvalence (outer-core) electronic shells should be left for explicit treatment, so that only inner (“small”) electronic cores can be replaced by RECPs. Conventional semilocal shape-consistent RECPs are not uniquely defined in the small-core case, and none of the possible definitions seems to be ideal. The origin of limited accuracy of semilocal models is considered in some detail. Substantial improvements are achieved through the use of a more general Ansätz for RECP operators implying the action of different potentials on the outer core and valence shells.