Possible geometrical structures and relative stability of alkaline-earth metal azido (HCaN₃)_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 (HCaN₃)_n (n＝1～5) clusters, the bond properties, charge distributions, vibration properties, and stability are analyzed. The calculated results show that the most optimized HCaN₃ has linear structure, and the most optimized structure for (HCaN₃)_n (n＝2～4) clusters are the planar ring formed by N atom and the Ca atom at cardinal extremity of nitrogen|the most optimized structure of (HCaN₃)₅ clusters is three-dimensional bell-shape. The middle Ca atoms of the most optimized structure show positive, H atom show negative. The middle N atoms of azido show positive, the N atoms at both ends of azido show negative, and the N atoms affected with Ca atoms directly show more negative. The IR spectra of the most optimized clusters have three vibration sections, the whole strongest vibration peak lies in 2193～2302 cm^－1, and the vibration mode is anti-symmetric stretching vibration of N—N bonds in azido. Stability analysis show that (HCaN₃)₃ clusters are more stable than other clusters.

Key words: (HCaN₃)_n (n＝1～5) clusters, azido, density functional theory, structure and property