Basis set convergence study of the calculations on (118) and $(118)_2$

Abstract

The last of 7p block element, (118), which is recently observed, is predicted to be a noble gas. The electron affinity of (118) and the spectroscopic constants of $(118)_2$ were calculated by the two-component Mφller-Plesset second-order perturbation and coupled-cluster methods with relativistic effective core potentials including spin-orbit operators. To investigate the basis set effects, a number of basis sets were constructed and used. Universal basis sets of Malli et al. were also used. The spin-orbit effects are found to give an electron affinity to (118) by the stabilization of the 8s shell, and to stabilze $(118)_2$ significantly. The calculated results depend strongly on the size of basis sets, and the diffuse functions seem to play an important role. Finally, $(118)_2$ was compared with other rare gas dimers. The spin-orbit splitting of 7p orbitals and the electron affinity are expected to make the bond strong.