Possible geometrical structures and relative stability of alkaline-earth metal azides (CaN₆)_n (n＝1～5) clusters are studied by using the hybrid density functional theory (B3LYP) with 6-311G* basis sets. For the most stable isomers of (CaN₆)_n (n＝1～5) clusters, the bond properties, charge distributions, vibrational properties, and stability are analyzed. The calculated results show that azido in azides has linear structure, the most optimized CaN₆ has linear structure, and the most optimized (CaN₆)_n (n＝2～5) clusters have chain structure of perpendicularity of approximate diamond composed by two azido with two Ca atoms. The middle N atoms of azido show positive, the N atoms at both ends of azido show negative, and the N atoms effected with Ca atoms directly show more negative. There is strong ionic bond between the Ca and N atoms. The IR spectra of the most optimized (CaN₆)_n (n＝1～5) clusters have four vibrational sections, the whole strongest vibrational peak lies in 2195～2280 cm^－1, and the vibrational mode is anti-symmetric stretching vibration of N—N bonds in azido. Stability analysis show that (CaN₆)₃ and (CaN₆)₅ clusters are more stable than other clusters.

Key words: (CaN₆)_n (n＝1～5) clusters, azido, density functional theory, structure and property