Spectroscopic constants of Pb and Eka-lead compounds: Comparison of different approaches

Three independent relativistic approaches, four-component density functional theory (4c-DFT), two-component DFT-ZORA(MP) (Zeroth order regular approximation with model potentials) and two-component ECP-CCSD(T) (Effective core potentials, coupled-cluster theory with singles, doubles and perturbative triples), have been employed by three independent groups to calculate the bond lengths, binding energies and vibrational frequencies for the eka-lead (E114) compounds E114X (X = H, F, Cl, Br, I, O, O₂) and the E114 dimer. For calibration, we also report results for homologous lead compounds. The dipole moments and dipole moment derivatives for the diatomic molecules are presented as well. The bonds in E114 compounds are considerably weaker than those of lead due to much larger relativistic (spin-orbit) effects It is predicted that E1140₂ is thermodynamically unstable with respect to the decomposition into E114 + O₂, in contrast to PbO₂ → Pb + O₂. Both 2PbO₂ → 2PbO + O₂ and 2E114O₂ → 2E114O + O₂ are thermodynamically unstable. The agreement between the two-component (ZORA) and the four-component (BDF) density functional results is quite good even for the E114 compounds. However, this requires a careful construction of the Gaussian basis sets used in the ZORA calculations.