Three isoelectronic families of X $$_4$$ Y $$_4$$ cubic systems

Abstract

We performed several types of ab initio calculations, from Hartree-Fock to Complete-Active-Space second-order perturbation theory and Coupled Cluster, on compact clusters of stoichiometry X \(_4\) Y \(_4\) , where X and Y are atoms belonging to the second row of the periodic table. More precisely, we considered the “cubic” structures of three isoelectronic groups, having a total of 48, 52, and 56-electrons, respectively. Notice that the highly symmetric cubic clusters of type X \(_8\) are characterized by an \(O_h\) symmetry group, while the X \(_4\) Y \(_4\) structures, with X \(\ne\) Y, have at most a \(T_d\) symmetry. Binding energies and wave function analysis of these clusters have been performed, in order to investigate the nature, and the electron delocalization of these systems and establish a comparison between them. To this purpose, we also computed the Total-Position Spread tensor for each structure, a quantity which is related to the multi-reference nature of a system wave function.