First-principles study of the geometrical and electronic structures of InnN2 (n = 1–10) clusters

The structures and electronic properties of InnN2 (n = 1–10) clusters have been investigated by density-functional theory with the generalized gradient approximation (GGA). The results indicate that increasing the coordination of indium atoms around the nitrogen, the competition between the nitrogen-nitrogen bond and the nitrogen-indium bond for InnN2 clusters, dominated by the former for n < 7, is reversed for n ⩾ 7. The structure motif starts to transform from the structural characteristics of comprising N2 unit to the characteristics with tetrahedral coordination of N atom from n = 6 to 7, and then the N atom with a bulklike coordination emerges. By Mulliken population analysis, the results indicate that In–N bond shows a partial ionic character in the InnN2 clusters (n ⩾ 7). The calculated results on the averaged binding energy, second-order difference of cluster energies, the vertical ionization potentials as well as the HOMO–LUMO gaps of the InnN2 clusters (n = 1–10) clusters indicate that the stability of In8N2 is the strongest of all the investigated clusters, due to stable cubic D2d structure. The averaged binding energies of InnN2 are high in comparison to those of InnN, implying that the stability of the clusters is remarkably enhanced by doping N.