A new generation of effective core potentials from correlated and spin-orbit calculations: selected transition metals and Lanthanides

We introduce new correlation consistent effective core potentials (ccECPs) for transition metals: Y, Zr, Nb, Rh, Ta, Re, Pt; Alkali metal: Cs; Lanthanides: Sm, Gd and Lu. For selected transition metals and Alkali metal, the s, p, and d orbital electrons with the highest and second highest principal quantum number are included in the valence space, while the valence space of Lanthanides additionally includes open-shell f-electrons. These ccECPs are given as a sum of spin-orbit averaged relativistic effective potential (AREP) and effective spin-orbit (SO) terms. The construction involves several steps with increasing refinements from more simple to fully correlated methods. The optimizations are carried out with objective functions that include weighted many-body atomic spectra and spin-orbit splittings. Transferability tests involve molecular binding curves of corresponding hydride and oxide dimers. The constructed ccECPs are systematically better and in a few cases on par with previous effective core potential (ECP) tables on all tested criteria and provide a significant increase in accuracy for valence-only calculations with these elements. Our study confirms the importance of the AREP part in determining the overall quality of the ECP even in the presence of sizable spin-orbit effects.

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