Inside a superatom: The M₇^q (M=Cu, Ag, q=1+, 0, 1-) case

All-electron relativistic density functional calculations are performed to obtain the electronic structure and nucleus-independent chemical shifts (NICS) of D_5h pentagonal-bipyramidal (PBP) Cu₇^q and Ag₇^q (q=1+,0,1) clusters. Scalar and spin-orbit relativistic effects are taken into account at two levels: the two-component zero-order regular approximation (ZORA) Hamiltonian and fully relativistic four-component calculations via the Dirac equation. These clusters are treated by including the spin-orbit effect in the jellium model, within the doublevalued point group (D_5h*) establishing the symmetry correlations between the molecular and the atomic spinors given by the full rotation group. These clusters show highly spherical aromaticity, which is suggested to increase the hardness of the superatom. Thus, the calculations suggest that the paramagnetic Cu₇ and Ag₇ clusters can be regarded as pseudohalogens.