Superalkali Cations with Trivalent Anion MF63- (M = Al, Ga, Sc) as Central Core

A new series of polynuclear cations MF6Li4+ (M = Al, Ga, Sc) have been theoretically investigated based on density functional theory calculations. The regular octahedral MF6 groups, although maintained their integrity, distorted to some degree upon the introduction of Li ligands. It has been found that the Li ligands prefer to occupy the bridge- or hollow-site of the MF6 core. According to the MP2 results, the MF6Li4+ cations have lower vertical electron affinities (EA(vert), 2.618-3.212 eV) than the threshold of 3.89 eV, verifying their superalkali identity. Besides, the MF6Li4+ configurations with more dispersive Li ligands possess lower EA(vert) values. More importantly, large HOMO-LUMO gaps, binding energies per atom (E-b), and positive fragmentation energies ensure the stability of these cations.