The intermolecular interaction between 3 and 4-dinitropyrazole (DNP) and cyclotetramethylene tetranitramine (HMX) was investigated at the level ot'M062X(D3)/6-311 + +G(d, p) in accordance with density functional theory. Six stable structures of DNP/HMX complex were obtained after optimization. Subsequently, electrostatic potential, electron density topology, reduced density gradient, and natural bond orbital were used to investigate the intermolecular interaction. Moreover, the effect of intermolecular interaction on the sensitivity of HMX was studied from different perspectives (e.g., the electron density at the critical point, the length of initiation bond, the bond order, the change of partial nitro charge, as well as the electron density difference). The results indicated that the interaction energy of the six complexes followed an order as follows: structure IV > structure I > structure III > structure VI > structure V > structure II. There were intermolecular hydrogen bonds of C-H … O and N-H…O and weak van der Waals forces of O…O and N…O in DNP/HMX complexes. The above intermolecular interactions in the complex increased the electron density and strength of the initiation bond in HMX molecule, thus resulting in the decrease of its sensitivity.
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