Electronic signature of the magicity and ionic bonding inAl13X(X=Li–K)clusters

Total energies and equilibrium geometries of neutral and anionic ${\mathrm{Al}}_{n}$ and ${\mathrm{Al}}_{n}X$ $(n=12--14,$ $X=\mathrm{Li},$ Na, K) clusters have been obtained following an optimization of their structure without any symmetry constraint. The calculations are based on molecular-orbital approach and the gradient-corrected density-functional theory. It is shown that although the binding energy of ${\mathrm{Al}}_{13}X$ clusters do not differ much from that of their neighbors, their ionization potentials, highest occupied molecular orbital and lowest unoccupied molecular orbital gaps, and electron affinities bear distinct signature of their magicity. That the binding of ${\mathrm{Al}}_{13}$ with alkali atoms is predominantly ionic is derived by comparing the electron affinity of ${\mathrm{Al}}_{13}X$ with other known salts.