A Fully Relativistic Study of the Geometry and Atomization Energy of Radium Dihalides by Coupled Cluster and Density Functional Theory Methods

The equilibrium geometries of radium dihalides RaX2 (X = F, Cl, Br) in their ground electronic state were found by the coupled cluster method with single and double cluster amplitudes and perturbative triples in the 4c framework. These data were compared to the geometries obtained by the density functional theory (DFT). Within the DFT framework, the atomization energy (AE) of radium dihalides was also calculated. Noticeable difference in AE values calculated with PBE0 and B3LYP exchange-correlation functionals was observed. The trend toward a decrease in the geometrical nonlinearity for heavy metal dihalides in the series F → Cl → Br is confirmed. In comparison to their homologs BaX2, compounds RaX2 have systematically lower AEs.