A new generation of effective core potentials: Selected heavy 5d and 6p elements

We develop correlation-consistent effective core potentials (ccECPs) and corresponding basis sets for selected heavy elements in the 5d (Hf, Os, Hg) and 6p (Tl, Po, At, Rn) blocks. This set completes the coverage of the ccECP library for the remaining 5d and 6p elements. Inclusion of pronounced relativistic effects, with spin-orbit coupling as a significant contributor, is crucial for describing the electronic structure with the desired accuracy. The ccECPs are constructed as a combination of averaged relativistic effective potentials (AREP) and the net spin-orbit valence operator. They are designed to eliminate the Coulomb cusp, providing smooth and bounded potentials expressed in gaussian expansions. The parameters are optimized to accurately capture electron correlation effects, including impact of core-valence correlations on valence properties, as well as to reproduce spin-orbit splittings. The constructions also take into account the need for low plane-wave energy cutoffs, ensuring both accuracy and computational viability across various electronic structure codes. We validate the performance of our ccECPs through benchmark calculations of atomic spectra and molecular properties, demonstrating excellent agreement with all-electron references within chemical accuracy bounds.