Comparisons of the theoretical calculation of nitrogen clusters by semiempirical MO method

Various nitrogen clusters, N_x, are selected for the present theoretical study. The number of nitrogen atoms chosen in this work varies from x = 8 to x = 32. PM3, which is known as one of the best semiempirical methods, is selected for the self-consistent molecular orbital calculations. The geometrical optimization, vibrational frequencies, and thermochemical computations are all involved for various types of molecular nitrogen clusters. The results show that all N_x's belong to the category of stable high-energy compounds. Comparison of average bond energy and delocalization energy of all cases reveals that N₂₀(I_h symmetry) is the most stable molecule among all the nitrogen clusters studied. In addition, our results show five-membered rings are the most favored in the structures of nitrogen clusters (N_x). © 1996 John Wiley & Sons, Inc.