Six optimized stable NTO dimers found on the potential energy surface and their electronic structures have been obtained by using density functional theory method at the B3LYP/6-311＋＋G** level. The intermolecular interaction energy was calculated with basis set superposition error correction and zero point energy correction. The greatest corrected intermolecular interaction energy of the dimer is －53.66 kJ/mol. Charge transfer between two subsystems is small. Natural bond orbital analysis was performed to reveal the origin of the interaction. Based on the vibrational analysis, the changes of thermodynamic properties from the monomer to dimer with the temperature ranging from 200.0 to 800.0 K have been obtained using the statistical thermodynamic method. It was found that the strong hydrogen bonds contribute to the dimers dominantly, while the binding energies are not only determined by hydrogen bonding. The dimerization process can occur spontaneously at lower or room temperature.

Key words: 3-nitro-1,2,4-triazol-5-one, intermolecular interaction, density functional theory, natural bond orbital analysis, thermodynamic property