Properties of closed-shell superheavy element hydrides and halides using coupled-cluster method and density functional theory with spin-orbit coupling.

We report bond lengths, force constants, and dissociation energies for a series of closed-shell superheavy element monohydrides and halides at the singles and doubles level with perturbative triples (CCSD(T)) using recently developed relativistic effective core potentials in this work. CCSD(T) results with spin-orbit coupling (SOC) included in self-consistent field (SCF) calculations provide highly accurate estimates for properties of these molecules. Trends as well as SOC effects on properties of these molecules are presented. Performance of the coupled-cluster (CC) approach with SOC included in post-SCF calculations (SOC-CC) on these superheavy element molecules is evaluated. Our results show that SOC-CCSD results are in excellent agreement with those of KR-CCSD, while the error of SOC-CCSD(T) is larger, particularly for molecules containing element 114. Density functional theory results with various exchange-correlation (XC) functionals for these superheavy element molecules are also compared with those of CCSD(T). PBE0 is shown to be able to give rise to results that agree best with those of CCSD(T) in scalar-relativistic calculations among the investigated XC functionals. On the other hand, B97-3 is the best XC functional when SOC is considered in calculations.