An ab initio investigation of the chemical vapor deposition of AlN from the AlCl3NH3 adduct is presented. Geometries, harmonic vibrational frequencies and relative energies for the AlCl3NH3 adduct, its dissociation products AlCln, NHn (n = 1-3), and ring and cluster compounds [(Cl2AlNH2)(n) (n = 1, 2), (ClAlNH)(n) (n = 1, 2, 3, 4, 6)] are discussed. The Al-N bond lengths in the investigated compounds are strongly dependent on the coordination numbers of the aluminum and nitrogen centers, decreasing from 2.0 Angstrom for 4-coordinated Al/N centers to 1.79 and 1.68 Angstrom for 3- and 2-coordinated Al/N centers, respectively. Thermodynamic analysis shows that dissociation of ClxAlNHx (x = 2, 3) compounds with elimination of HCl and simultaneous formation of oligomeric forms is preferable to the process of dissociation into components or simple HCl detachment. Under standard conditions gaseous 4-coordinated Al/N compounds (ClAlNH)(6) and (ClAlNH)(4) are more stable than 3-coordinated (ClAlNH)(2) and (ClAlNH)(3) compounds. In 4-membered rings and clusters, the electrostatic repulsion between nearby Al-Al and N-N atoms makes reorganization to 6-membered rings extremely favorable. The suggested mechanism of AlN deposition involving cluster formation in the gas phase is discussed.