The van der Waals interactions in systems involving superheavy elements: the case of oganesson (Z = 118)

This work presents a study involving dimers composed of He, Ne, Ar, Kr, Xe, Rn, and Og noble gases with oganesson, a super-heavy closed-shell element (Z = 118). He-Og, Ne-Og, Ar-Og, Kr-Og, Xe-Og, Rn-Og, and Og-Og ground state electronic potential energy curves were calculated based on the 4-component (4c) Dirac-Coulomb Hamiltonian and were counterpoise corrected. For the 4c calculations, the electron correlation was taken into account using the same methodology (MP2-srLDA) and basis set quality (Dyall's acv3z and Dunning's aug-cc-PVTZ). All calculations included quantum electrodynamics effects at the Gaunt interaction level. For all the aforementioned dimers the vibration energies, spectroscopic constants (ω_e, ω_ex_e, ω_ey_e, α_e, and γ_e), and lifetime as a function of the temperature (which ranged from 200 to 500 K) were also calculated. The obtained results suggest that the inclusion of quantum electrodynamics effects reduces the value of the dissociation energy of all hetero-nuclear molecules with a percentage contribution ranging from 0.48% (for the He-Og dimer) to 9.63% (for the Rn-Og dimer). The lifetime calculations indicate that the Og-He dimer is close to the edge of instability and that Ng-Og dimers are relatively less stable when the Gaunt correction is considered. Exploiting scaling laws that adopt the polarizability of involved partners as scaling factors, it has also been demonstrated that in such systems the interaction is of van der Waals nature (size repulsion plus dispersion attraction) and this permitted an estimation of dissociation energy and equilibrium distance in the Og-Og dimer. This further information has been exploited to evaluate the rovibrational levels in this symmetric dimer and to cast light on the macroscopic properties of condensed phases concerning the complete noble gas family, emphasizing some anomalies of Og.