Energetic materials are aggregative and mixed, systems. The intermolecular interactions play significant roles in the physical, chemical and explosive property. The study on intermolecular interactions of energetic materials has attracted wide attention. The organic azides. are an important category of energetic materials and widely used in many fields. Ethyl azide is the simple model having the explosive property for the organic azides energetic compound. Ethyl azide monomer (I) and all its possible stable clusters (II, III and IV) are fully optimized by ab initio method at the HF/6-311 ++ G ** level. Vibrational frequencies calculated to ascertain each structure are characterized to be the stable structure (no imaginary frequencies). The proportions of correlated interaction energies to their total interaction energies DeltaE(MP2) are 65.14%, 63.76% and 65.62% for II, III and IV respectively. In addition, the basis set superposition error (BSSE) correction energies are 7.82, 7.61 and 4.40 kJ/mol for II, III and IV respectively. The zero point energy (ZPE) corrections for the interaction energies are much less than those of MP2 electron correlation and BSSE correction energies. After MP2 electron correlation correction, BSSE and ZPE correction, the greatest corrected intermolecular interaction of the dimers is - 10.45 kJ/mol. The charge redistribution mainly occurs on the adjacent N...H atoms between submolecules. The charge transfer between two subsystems is very small. Natural bond orbital (NBO) analysis is performed to reveal the origin of the interaction. Based on the statistical thermodynamic method, the standard thermodynamic functions, heat capacities (C-p(0)) entropies (S-m(0)) and enthalpies (H-m(0)) and the changes of thermodynamic properties from the monomer to dimer with the temperatures ranging from 200.00 K to 800.00 K have been obtained.
